Shallow Thoughts : tags : astronomy

Akkana's Musings on Open Source Computing and Technology, Science, and Nature.

Sat, 14 Oct 2023

Annular Eclipse Party

[Annular eclipse, afocal with cellphone camera through H-alpha scope] The path for the Oct 14, 2023 annular eclipse passed right over my house. What luck!

We'd driven a few hours to see the last annular eclipse, in 2012, from Red Bluff, CA. The opportunity to see one from home, without needing to drive anywhere, was not to be missed.

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[ 19:22 Oct 14, 2023    More science/astro | permalink to this entry | ]

Sat, 28 May 2022

Monday night: Tau Herculid Meteor Shower, Possible Storm

There's some talk that a usually obscure meteor shower, the Tau Herculids, may this year become a meteor storm.

For details, see EarthSky News: Will the Tau Herculid meteors produce a storm?

The Tau Herculids come from periodic Comet 73P/Schwassmann-Wachmann, which in 1995, began to break up, creating lots of debris scattered across its orbit. It's hard to know exactly where the fragments ended up ... but comet experts like Don Machholz think there's a good chance that we'll be passing through an unusually dense clump of particles when we cross 73P's orbit this year.

I'm not a big meteor watcher — I find most meteor showers distinctly underwhelming. But in November 2002, I was lucky enough to view the Leonid meteor storm from Fremont Peak, near San Juan Bautista, CA.

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[ 17:42 May 28, 2022    More science/astro | permalink to this entry | ]

Mon, 07 Mar 2022

The Sun is Spectacular Today in H-Alpha

[Sun in h-alpha on 2222-03-07] A couple of years ago, Dave and I acquired an H-alpha solar scope.

Neither of us had been much of a solar observer. We'd only had white-light filters: filters you put over the front of a regular telescope to block out most of the sun's light so you can see sunspots.

H-alpha filters are a whole different beast: you can see prominences, those huge arcs of fire that reach out into space for tens of thousands of miles, many times the size of the Earth. And you can also see all sorts of interesting flares and granulation on the surface of the sun, something only barely hinted at in white-light images.

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[ 12:00 Mar 07, 2022    More science/astro | permalink to this entry | ]

Sun, 06 Jun 2021

Fiddling with JavaScript Astronomy: ThreeWorlds

[analemma webapp] I have another PEEC Planetarium talk coming up in a few weeks, a talk on the summer solstice co-presenting with Chick Keller on Fri, Jun 18 at 7pm MDT.

I'm letting Chick do most of the talking about archaeoastronomy since he knows a lot more about it than I do, while I'll be talking about the celestial dynamics -- what is a solstice, what is the sun doing in our sky and why would you care, and some weirdnesses relating to sunrise and sunset times and the length of the day. And of course I'll be talking about the analemma, because just try to stop me talking about analemmas whenever the topic of the sun's motion comes up.

But besides the analemma, I need a lot of graphics of the earth showing the terminator, the dividing line between day and night.

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[ 18:33 Jun 06, 2021    More science/astro | permalink to this entry | ]

Wed, 07 Oct 2020

MarsMap: What Features of Mars are Visible?

[MarsMap screenshot] I've been working on my upcoming PEEC talk, Observing Mars at Opposition on October 16.

Mars' closest approach was yesterday, October 6, and the actual opposition will be next Tuesday, October 13.

So, wait, we've already missed closest approach, and the opposition will be over before the actual talk happens? Then why bother?

Fortunately, opposition is actually an "opposition season", not a single date. And for most people, the best part is a little past opposition.

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[ 18:10 Oct 07, 2020    More science/astro | permalink to this entry | ]

Sat, 25 Jul 2020

S is for Starlink Satellites

[Comet Neowise and Starlink Satellites] Monday was the last night it's been clear enough to see Comet Neowise. I shot some photos with the Rebel, but I haven't quite figured out the alignment and stacking needed for decent astrophotos, so I don't have much to show. I can't even see the ion tail.

The interesting thing about Monday besides just getting to see the comet was the never-ending train of satellites.

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[ 20:27 Jul 25, 2020    More science/astro | permalink to this entry | ]

Thu, 16 Jul 2020

Comet C/2020 F3 NEOWISE in the evening sky

[Comet C2020 F3 NEOWISE the morning of 2020-07-16 from White Rock, NM] Comet C/2020 F3 NEOWISE continues to improve, and as of Tuesday night it has moved into the evening sky (while also still being visible in the morning for a few more days).

I caught it Tuesday night at 9:30 pm. The sky was still a bit bright, and although the comet was easy in binoculars, it was a struggle to see it with the unaided eye. However, over the next fifteen minutes the sky darkened, and it looked pretty good by 9:50, considering the partly cloudy sky. I didn't attempt a photograph; this photo is from Sunday morning, in twilight and with a bright moon.

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[ 12:58 Jul 16, 2020    More science/astro | permalink to this entry | ]

Sat, 11 Jul 2020

Comet C2020 F3 NEOWISE in the Morning (and eventually, the evening)

[Comet C2020F3 NEOWISE over California desert landscape, by Dbot3000]
Comet C2020F3 NEOWISE over California desert landscape. Photo by Dbot3000

I've learned not to get excited when I read about a new comet. They're so often a disappointment. That goes double for comets in the morning sky: I need a darned good reason to get up before dawn.

But the chatter among astronomers about the current comet, C2020 F3 NEOWISE, has been different. So when I found myself awake at 4 am, I grabbed some binoculars and went out on the deck to look.

And I was glad I did. NEOWISE is by far the best comet I've seen since Hale-Bopp. Which is not to say it's in Hale-Bopp's class -- certainly not. But it's easily visible to the unaided eye, with a substantial several-degree-long tail. Even in dawn twilight. Even with a bright moon. It's beautiful!

Update: the morning after I wrote that, I did get a photo, though it's not nearly as good as Dbot3000's that's shown here.


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[ 18:18 Jul 11, 2020    More science/astro | permalink to this entry | ]

Sat, 20 Jun 2020

Solstice Sun Dagger

Today is the summer solstice. Happy solstice!

[Solstice sun dagger] When I was in grade school -- probably some time around 7th grade -- I happened upon an article in Scientific American about the Anasazi Sun Dagger on Fajada Butte in Chaco Canyon. On the solstices and equinoxes, a thin dagger of light is positioned just right so that it moves across a spiral that's carved into the rock.

I was captivated. What an amazing sight it must be, I thought. I wondered if ordinary people were allowed to go see it.

Well, by the time I was old enough to do my own traveling, the answer was pretty much no. Too many people were visiting Fajada Butte ...

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[ 17:35 Jun 20, 2020    More science/astro | permalink to this entry | ]

Sun, 01 Mar 2020

Plotting Epicycles

Galen Gisler, our master of Planetarium Tricks, presented something strange and cool in his planetarium show last Friday.

[inner planet orbits from north ecliptic pole, with Venus pentagram] He'd been looking for a way to visualize the "Venus Pentagram", a regularity where Venus' inferior conjunctions -- the point where Venus is approximately between Earth and the Sun -- follow a cycle of five. If you plot the conjunction positions, you'll see a pentagram, and the sixth conjunction will be almost (but not quite) in the same place where the first one was. Supposedly many ancient civilizations supposedly knew about this pattern, though as Galen noted (and I'd also noticed when researching my Stonehenge talk), the evidence is sometimes spotty.

Galen's latest trick: he moved the planetarium's observer location up above the Earth's north ecliptic pole. Then he told the planetarium to looked back at the Earth and lock the observer's position so it moves along with the Earth; then he let the planets move in fast-forward, leaving trails so their motions were plotted.

The result was fascinating to watch. You could see the Venus pentagram easily as it made its five loops toward Earth, and the loops of all the other planets as their distance from Earth changed over the course of both Earth's orbits and theirs.

You can see the patterns they make at right, with the Venus pentagram marked (click on the image for a larger version). Venus' orbit is white, Mercury is yellow, Mars is red. If you're wondering why Venus' orbit seems to go inside Mercury's, remember: this is a geocentric model, so it's plotting distance from Earth, and Venus gets both closer to and farther from Earth than Mercury does.

He said he'd shown this to the high school astronomy club and their reaction was, "My, this is complicated." Indeed. It gives insight into what a difficult problem geocentric astronomers had in trying to model planetary motion, with their epicycles and other corrections.

Of course that made me want one of my own. It's neat to watch it in the planetarium, but you can't do that every day.

So: Python, Gtk/Cairo, and PyEphem. It's pretty simple, really. The goal is to plot planet positions as viewed from high above the north ecliptic pole: so for each time step, for each planet, compute its right ascension and distance (declination doesn't matter) and convert that to rectangular coordinates. Then draw a colored line from the planet's last X, Y position to the new one. Save all the coordinates in case the window needs to redraw.

[planet orbits from north ecliptic pole] At first I tried using Skyfield, the Python library which is supposed to replace PyEphem (written by the same author). But Skyfield, while it's probably more accurate, is much harder to use than PyEphem. It uses SPICE kernels (my blog post on SPICE, some SPICE examples and notes), which means there's no clear documentation or list of which kernels cover what. I tried the kernels mentioned in the Skyfield documentation, and after running for a while the program died with an error saying its model for Jupiter in the de421.bsp kernel wasn't good beyond 2471184.5 (October 9 2053).

Rather than spend half a day searching for other SPICE kernels, I gave up on Skyfield and rewrote the program to use PyEphem, which worked beautifully and amazed me with how much faster it was: I had to rewrite my GTK code to use a timer just to slow it down to where I could see the orbits as they developed!

It's fun to watch; maybe not quite as spacey as Galen's full-dome view in the planetarium, but a lot more convenient. You need Python 3, PyEphem and the usual GTK3 introspection modules; on Debian-based systems I think the python3-gi-cairo package will pull in most of them as dependencies.

Plot your own epicycles: epicycles.py.

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[ 13:04 Mar 01, 2020    More science/astro | permalink to this entry | ]

Tue, 10 Dec 2019

Planetarium Show Friday: Hitchhiker's Guide to the Moon

[Schroter's Valley on the Moon] This Friday, Dave and I will be presenting a planetarium show called The Hitchhiker's Guide to the Moon: Visit the Moon Without Leaving Your Home Planet.

I'm jazzed about this show. I think it'll be the most fun planetarium show we've given so far. We'll be showing a variety of lunarfeatures: maria, craters, mountains, rilles, domes, catenae and more. For each one, we'll discuss what the feature actually is and how it was created, where to see good examples on the moon, and -- the important part -- where you can go on Earth, and specifically in the Western US, to see a similar feature up close.

Plus: a short flyover of some of the major features using the full-dome planetarium. Some features, like Tycho, the Straight Wall, Reiner Gamma, plus lots of rilles, look really great in the planetarium.

If you can't get to the moon yourself, this is the next best thing!

The Hitchhiker's Guide to the Moon: 7pm at the PEEC nature center. Admission is free. Come find out how to explore the moon without leaving your home planet!

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[ 18:06 Dec 10, 2019    More science/astro | permalink to this entry | ]

Mon, 11 Nov 2019

Mercury Transit: Comparing Between H-alpha and White Light

[Mercury transit 11/11/2019] The Mercury transit is over. But we learned some interesting things.

I'd seen Mercury transits before, but this is the first time we had an H-alpha scope (a little 50mm Coronado PST) in addition to a white light filter (I had my 102mm refractor set up with the Orion white-light filter).

As egress approached, Dave was viewing in the H-alpha while I was on the white light scope. When I saw the black-drop effect at third contact, Mercury was still nowhere near the edge in the H-alpha: the H-alpha shows more of the solar atmosphere so the sun's image is noticably bigger. This was the point when we realized that we should have expected this and been timing and recording. Alas, it was too late.

Mercury was roughly 60% out in the white light filter -- just past the point where the "bite" it made in the limb of the sun -- by the time Dave called out third contact. We guessed it was roughly a minute, but that could be way off.

For fourth contact, Dave counted roughly 45 seconds between when I couldn't see Mercury any more and when he lost track of it. This is pretty rough, because it was windy, seeing was terrible and there was at least a 15-second slop when I wasn't sure if I could any indentation in the limb; I'm sure it was at least as hard in the Coronado, which was running at much lower magnification.

So we had a chance to do interesting science and we flubbed it. And the next chance isn't til 2032; who knows if we'll still be actively observing then.

I wanted to at least correlate those two numbers: 45 seconds and 60% of a Mercury radius.

Mercury is about 10" (arcseconds) right now. That was easy to find. But how fast does it move? I couldn't find anything about that, searching for terms like mercury transit angular speed OR velocity. I tried to calculate it with PyEphem but got a number that was orders of magnitude off. Maybe I'll figure it out for a later article, but I wanted to get this posted quickly.

[Mercury transit 11/11/2019 in H-alpha] I didn't spend much time trying photography. I got a couple afocal snaps with my pocket digital camera through the white-light scope that worked out pretty well. I wasn't sure that would work for the Coronado: the image is fairly dim. The snaps I did get show Mercury, though none of the interesting detail like faculae and the one tiny prominence that was visible. But the interesting thing is the color. To the eye, the H-alpha scope image is a slightly orangy red, but in the digital camera it came out a startling purplish pink. This may be due to the digital camera's filters passing some IR, confusing the algorithms that decide how to shift the color. Of course, I could have adjusted the color in GIMP back to the real color, but I thought it was more interesting to leave it the hue it came out of the camera. (I did boost contrast and run an unsharp mask filter, to make it easier to see Mercury.)

Anyway, fun and unexpectedly edifying! I wish we had another transit happening sooner than 2032.

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[ 12:15 Nov 11, 2019    More science/astro | permalink to this entry | ]

Fri, 08 Nov 2019

Mercury Transit Next Monday

[Mercury Transit 2006, photo by Brocken Inaglory]
Mercury Transit 2006, photo by Brocken Inaglory
Next Monday, November 11, is a transit of Mercury across the sun.

Mercury transits aren't super rare -- not once- or twice-in-a-lifetime events like Venus transits -- but they're not that common, either. The last Mercury transit was in 2016; the next one won't happen til 2032.

This year's transit isn't ideal for US observers. The transit will already be well underway by the time the sun rises, at least in the western US. Here in New Mexico (Mountain time), the sun rises with Mercury transiting, and the transit lasts until 11:04 MST. Everybody else, check timeanddate's Mercury Transit page for your local times.

Mercury is small, unfortunately, so it's not an easy thing to see without magnification. Of course, you know that you should never look at the sun without an adequate filter. But even if you have safe "eclipse glasses", it may be tough to spot Mercury's small disk against the surface of the sun.

[binocular projection of a solar eclipse] One option is to take some binoculars and use them to project an image. Point the big end of the binoculars at the sun, and the small end at a white surface, preferably leaning so it's perpendicular to the sun. I don't know if binocular projection will give a big enough image to show Mercury, so a very smooth and white background, tilted so it's perpendicular to the sun, will help. (Don't be tempted to stick eclipse glasses in front of a binocular or telescope and look through the eyepiece! Stick to projection unless you have filters specifically intended for telescopes or binoculars.)

Of course, a telescope with a safe solar filter is the best way to see a transit. If you're in the Los Alamos area, I hear the Pajarito Astronomers are planning to set up telescopes at Overlook Park. They don't seem to have announced it in any of the papers yet, but I see it listed on the Pajarito Astronomers website. There's also an event planned at the high school where the students will be trying to time Mercury's passage, but I don't know if that's open to the public. Elsewhere in the world, check with your local astronomy club for Mercury transit parties: I'm sure most clubs have something planned.

I was discussing the transit with a couple of local astronomers earlier this week, and one of them related it to the search for exoplanets. One of the main methods of detecting exoplanets is to measure the dimming of a star's light as a planet crosses its face. For instance, in 55 Cancri e, you can see a dimming as the planet crosses the star's face, and a much more subtle dimming when the planet disappears behind the star. As Mercury crosses the Sun's face, it blocks some of the sun's light in the same way. By how much?

The radius of Mercury is 0.0035068 solar radii, and the dimming is proportional to area so it should be 0.00350682, or 0.0000123, a 0.00123% dimming. Not very much!

But it looks like in the 55 Cancri e case, they're detecting dips of around .001% -- it seems amazing that you could detect a planet as small as Mercury this way (and certainly the planet is much bigger in the case of 55 Cancri e) ... but maybe it's possible.

Anyway, it's fun to think about exoplanets as you watch tiny Mercury make its way across the face of the Sun. Wherever you are, I hope you get a chance to look!

Update: A report from the transit: Mercury Transit: Comparing Between H-alpha and White Light.

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[ 11:36 Nov 08, 2019    More science/astro | permalink to this entry | ]

Thu, 01 Aug 2019

Silly Moon Names: a Nice Beginning Python Project

Every time the media invents a new moon term -- super blood black wolf moon, or whatever -- I roll my eyes.

[Lunar Perigee and Apogee sizes] First, this ridiculous "supermoon" thing is basically undetectable to the human eye. Here's an image showing the relative sizes of the absolute closest and farthest moons. It's easy enough to tell when you see the biggest and smallest moons side by side, but when it's half a degree in the sky, there's no way you'd notice that one was bigger or smaller than average.

Even better, here's a link to an animation of how the moon changes size and "librates" -- tilts so that we can see a little bit over onto the moon's far side -- during the course of a month.

Anyway, the media seem to lap this stuff up and every month there's a new stupid moon term. I'm sure nearly every astronomer was relieved to see the thoroughly sensible Gizmodo article yesterday, Oh My God Stop It With the Fake Moon Names What the Hell Is a 'Black Moon' That Isn't Anything. Not that that will stop the insanity.

If You Can't Beat 'Em, Join 'Em

And then, talking about the ridiculous moon name phenom with some friends, I realized I could play this game too. So I spent twenty minutes whipping up my own Silly Moon Name Generator.

It's super simple -- it just uses Linux' built-in dictionary, with no sense of which words are common, or adjectives or nouns or what. Of course it would be funnier with a hand-picked set of words, but there's a limit to how much time I want to waste on this.

You can add a parameter ?nwords=5 (or whatever number) if you want more or fewer words than four.

How Does It Work?

Random phrase generators like this are a great project for someone just getting started with Python. Python is so good at string manipulation that it makes this sort of thing easy: it only takes half a page of code to do something fun. So it's a great beginner project that most people would probably find more rewarding than cranking out Fibonacci numbers (assuming you're not a Fibonacci geek like I am). For more advanced programmers, random phrase generation can still be a fun and educational project -- skip to the end of this article for ideas.

For the basics, this is all you need: I've added comments explaining the code.

import random


def hypermoon(filename, nwords=4):
    '''Return a silly moon name with nwords words,
       each taken from a word list in the given filename.
    '''
    fp = open(filename)
    lines = fp.readlines()

    # A list to store the words to describe the moon:
    words = []
    for i in range(nwords):    # This will be run nwords times
        # Pick a random number between 0 and the number of lines in the file:
        whichline = random.randint(0, len(lines))

        # readlines() includes whitespace like newline characters.
        # Use whichline to pull one line from the file, and use
        # strip() to remove any extra whitespace:
        word = lines[whichline].strip()

        # Append it to our word list:
        words.append(word)

    # The last word in the phrase will be "moon", e.g.
    # super blood wolf black pancreas moon
    words.append("moon")

    # ' '.join(list) combines all the words with spaces between them
    return ' '.join(words)


# This is called when the program runs:
if __name__ == '__main__':
    random.seed()

    print(hypermoon('/usr/share/dict/words', 4))

A More Compact Format

In that code example, I expanded everything to try to make it clear for beginning programmers. In practice, Python lets you be a lot more terse, so the way I actually wrote it was more like:

def hypermoon(filename, nwords=4):
    with open(filename, encoding='utf-8') as fp:
        lines = fp.readlines()

    words = [ lines[random.randint(0, len(lines))].strip()
              for i in range(nwords) ]
    words.append('moon')
    return ' '.join(words)

There are three important differences (in bold):

Opening a file using "with" ensures the file will be closed properly when you're done with it. That's not important in this tiny example, but it's a good habit to get into.

I specify the 'utf-8' encoding when I open the file because when I ran it as a web app, it turned out the web server used the ASCII encoding and I got Python errors because there are accented characters in the dictionary somewhere. That's one of those Python annoyances you get used to when going beyond the beginner level.

The way I define words all in one line (well, it's conceptually one long line, though I split it into two so each line stays under 72 characters) is called a list comprehension. It's a nice compact alternative to defining an empty list [] and then calling append() a bunch of times, like I did in the first example.

Initially they might seem harder to read, but list comprehensions can actually make code clearer once you get used to them.

A Python Driven Web Page

Finally, to make it work as a web page, I added the CGI module. That isn't really a beginner thing so I won't paste it here, but you can see the CGI version at hypermoon.py on GitHub.

I should mention that there's some debate over CGI in Python. The movers and shakers in the Python community don't approve of CGI, and there's a plan to remove it from upcoming Python versions. The alternative is to use technologies like Flask or Django. while I'm a fan of Flask and have used it for several projects, it's way overkill for something like this, mostly because of all the special web server configuration it requires (and Django is far more heavyweight than Flask). In any case, be aware that the CGI module may be removed from Python's standard library in the near future. With any luck, python-cgi will still be available via pip install or as Linux distro packages.

More Advanced Programmers: Making it Funnier

I mentioned earlier that I thought the app would be a lot funnier with a handpicked set of words. I did that long, long ago with my Star Party Observing Report Generator (written in Perl; I hadn't yet started using Python back in 2001). That's easy and fun if you have the time to spare, or a lot of friends contributing.

You could instead use words taken from a set of input documents. For instance, only use words that appear in Shakespeare's plays, or in company mission statements, or in Wikipedia articles about dog breeds (this involves some web scraping, but Python is good at that too; I like BeautifulSoup).

Or you could let users contribute their own ideas for good words to use, storing the user suggestions in a database.

Another way to make the words seem more appropriate and less random might be to use one of the many natural language packages for Python, such as NLTK, the Natural Language Toolkit. That way, you could control how often you used adjectives vs. nouns, and avoid using verbs or articles at all.

Random word generators seem like a silly and trivial programming exercise -- because they are! But they're also a fun starting point for more advanced explorations with Python.

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[ 14:24 Aug 01, 2019    More humor | permalink to this entry | ]

Thu, 13 Jun 2019

Finding Astronomical Alignments in Ancient Monuments (or anywhere else)

Dave and I will be presenting a free program on Stonehenge at the Los Alamos Nature Center tomorrow, June 14.

The nature center has a list of programs people have asked for, and Stonehenge came up as a topic in our quarterly meeting half a year ago. Remembering my seventh grade fascination with Stonehenge and its astronomical alignments -- I discovered Stonehenge Decoded at the local library, and built a desktop model showing the stones and their alignments -- I volunteered. But after some further reading, I realized that not all of those alignments are all they're cracked up to be and that there might not be much of astronomical interest to talk about, and I un-volunteered.

But after thinking about it for a bit, I realized that "not all they're cracked up to be" makes an interesting topic in itself. So in the next round of planning, I re-volunteered; the result is tomorrow night's presentation.

The talk will include a lot of history of Stonehenge and its construction, and a review of some other important or amusing henges around the world. But this article is on the astronomy, or lack thereof.

The Background: Stonehenge Decoded

Stonehenge famously aligns with the summer solstice sunrise, and that's when tens of thousands of people flock to Salisbury, UK to see the event. (I'm told that the rest of the time, the monument is fenced off so you can't get very close to it, though I've never had the opportunity to visit.)

Curiously, archaeological evidence suggests that the summer solstice wasn't the big time for prehistorical gatherings at Stonehenge; the time when it was most heavily used was the winter solstice, when there's a less obvious alignment in the other direction. But never mind that.

[Gerald Hawkins' Stonehenge alignments from Stonehenge Decoded] In 1963, Gerald Hawkins wrote an article in Nature, which he followed up two years later with a book entitled Stonehenge Decoded. Hawkins had access to an IBM 7090, capable of a then-impressive 100 Kflops (thousand floating point operations per second; compare a Raspberry Pi 3 at about 190 Mflops, or about a hundred Gflops for something like an Intel i5). It cost $2.9 million (nearly $20 million in today's dollars).

Using the 7090, Hawkins mapped the positions of all of Stonehenge's major stones, then looked for interesting alignments with the sun and moon. He found quite a few of them. (Hawkins and Fred Hoyle also had a theory about the fifty-six Aubrey holes being a lunar eclipse predictor, which captured my seventh-grade imagination but which most researchers today think was more likely just a coincidence.)

But I got to thinking ... Hawkins mapped at least 38 stones if you don't count the Aubrey holes. If you take 38 randomly distributed points, what are the chances that you'll find interesting astronomical alignments?

A Modern Re-Creation of Hawkins' Work

Programmers today have it a lot easier than Hawkins did. We have languages like Python, with libraries like PyEphem to handle the astronomical calculations. And it doesn't hurt that our computers are about a million times faster.

Anyway, my script, skyalignments.py takes a GPX file containing a list of geographic coordinates and compares those points to sunrise and sunset at the equinoxes and solstices, as well as the full moonrise and moonset nearest the solstice or equinox. It can find alignments among all the points in the GPX file, or from a specified "observer" point to each point in the file. It allows a slop of a few degrees, 2 degrees by default; this is about four times the diameter of the sun or moon, but a half-step from your observing position can make a bigger difference than that. I don't know how much slop Hawkins used; I'd love to see his code.

[Astronomical alignments between pairs of New Mexico peaks] My first thought was, what if you stand on a mountain peak and look around you at other mountain peaks? (It's easy to get GPS coordinates for peaks; if you can't find them online you can click on them on a map.) So I plotted the major peaks in the Jemez and Sangre de Cristo mountains that I figured were all mutually visible. It came to 22 points; about half what Hawkins was working with.

My program found (114 alignments.

[Astronomical alignments between pairs of New Mexico peaks] Yikes! Way too many. What if I cut it down? So I tried eliminating all but the really obvious ones, the ones you really notice from across the valley. The most prominent 11 peaks: 5 in the Jemez, 6 in the Sangres.

That was a little more manageable. Now I was down to only 22 alignments.

Now, I'm pretty sure that the Ancient Ones -- or aliens -- didn't lay out the Jemez and Sangre de Cristo mountains to align with the rising and setting sun and moon. No, what this tells us is that pretty much any distribution of points will give you a bunch of astronomical alignments.

And that's just the sun and moon, all Hawkins was considering. If you look for writing on astronomical alignments in ancient monuments, you'll find all people claiming to have found alignments with all sorts of other rising and setting bodies, like Sirius and Orion's belt. Imagine how many alignments I could have found if I'd included the hundred brightest stars.

So I'm not convinced. Certainly Stonehenge's solstice alignment looks real; I'm not disputing that. And there are lots of other archaeoastronomy sites that are even more convincing, like the Chaco sun dagger. But I've also seen plenty of web pages, and plenty of talks, where someone maps out a collection of points at an ancient site and uses alignments among them as proof that it was an ancient observatory. I suspect most of those alignments are more evidence of random chance and wishful thinking than archeoastronomy.

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[ 14:54 Jun 13, 2019    More science/astro | permalink to this entry | ]

Sun, 23 Sep 2018

Writing Solar System Simulations with NAIF SPICE and SpiceyPy

Someone asked me about my Javascript Jupiter code, and whether it used PyEphem. It doesn't, of course, because it's Javascript, not Python (I wish there was something as easy as PyEphem for Javascript!); instead it uses code from the book Astronomical Formulae for Calculators by Jean Meeus. (His better known Astronomical Algorithms, intended for computers rather than calculators, is actually harder to use for programming because Astronomical Algorithms is written for BASIC and the algorithms are relatively hard to translate into other languages, whereas Astronomical Formulae for Calculators concentrates on explaining the algorithms clearly, so you can punch them into a calculator by hand, and this ends up making it fairly easy to implement them in a modern computer language as well.)

Anyway, the person asking also mentioned JPL's page HORIZONS Ephemerides page, which I've certainly found useful at times. Years ago, I tried emailing the site maintainer asking if they might consider releasing the code as open source; it seemed like a reasonable request, given that it came from a government agency and didn't involve anything secret. But I never got an answer.

[SpiceyPy example: Cassini's position] But going to that page today, I find that code is now available! What's available is a massive toolkit called SPICE (it's all in capitals but there's no indication what it might stand for. It comes from NAIF, which is NASA's Navigation and Ancillary Information Facility).

SPICE allows for accurate calculations of all sorts of solar system quantities, from the basic solar system bodies like planets to all of NASA's active and historical public missions. It has bindings for quite a few languages, including C. The official list doesn't include Python, but there's a third-party Python wrapper called SpiceyPy that works fine.

The tricky part of programming with SPICE is that most of the code is hidden away in "kernels" that are specific to the objects and quantities you're calculating. For any given program you'll probably need to download at least four "kernels", maybe more. That wouldn't be a problem except that there's not much help for figuring out which kernels you need and then finding them. There are lots of SPICE examples online but few of them tell you which kernels they need, let alone where to find them.

After wrestling with some of the examples, I learned some tricks for finding kernels, at least enough to get the basic examples working. I've collected what I've learned so far into a new GitHub repository: NAIF SPICE Examples. The README there explains what I know so far about getting kernels; as I learn more, I'll update it.

SPICE isn't easy to use, but it's probably much more accurate than simpler code like PyEphem or my Meeus-based Javascript code, and it can calculate so many more objects. It's definitely something worth knowing about for anyone doing solar system simulations.

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[ 16:43 Sep 23, 2018    More programming | permalink to this entry | ]

Fri, 23 Feb 2018

PEEC Planetarium Show: "The Analemma Dilemma"

[Analemma by Giuseppe Donatiello via Wikimedia Commons] Dave and I are giving a planetarium show at PEEC tonight on the analemma.

I've been interested in the analemma for years and have written about it before, here on the blog and in the SJAA Ephemeris. But there were a lot of things I still didn't understand as well as I liked. When we signed up three months ago to give this talk, I had plenty of lead time to do more investigating, uncovering lots of interesting details regarding the analemmas of other planets, the contributions of the two factors that go into the Equation of Time, why some analemmas are figure-8s while some aren't, and the supposed "moon analemmas" that have appeared on the Astronomy Picture of the Day. I added some new features to the analemma script I'd written years ago as well as corresponding with an expert who'd written some great Equation of Time code for all the planets. It's been fun.

I'll write about some of what I learned when I get a chance, but meanwhile, people in the Los Alamos area can hear all about it tonight, at our PEEC show: The Analemma Dilemma, 7 pm tonight, Friday Feb 23, at the Nature Center, admission $6/adult, $4/child.

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[ 10:23 Feb 23, 2018    More science/astro | permalink to this entry | ]

Sun, 27 Aug 2017

Total Eclipse

[2017 Solar eclipse with corona] My first total eclipse! The suspense had been building for years.

Dave and I were in Wyoming. We'd made a hotel reservation nine months ago, by which time we were already too late to book a room in the zone of totality and settled for Laramie, a few hours' drive from the centerline.

For visual observing, I had my little portable 80mm refractor. But photography was more complicated. I'd promised myself that for my first (and possibly only) total eclipse, I wasn't going to miss the experience because I was spending too much time fiddling with cameras. But I couldn't talk myself into not trying any photography at all.

Initially, my plan was to use my 90mm Mak as a 500mm camera lens. It had worked okay for the the 2012 Venus transit.

[Homemade solar finder for telescope] I spent several weeks before the eclipse in a flurry of creation, making a couple of solar finders, a barn-door mount, and then wrestling with motorizing the barn-door (which was a failure because I couldn't find a place to buy decent gears for the motor. I'm still working on that and will eventually write it up). I wrote up a plan: what equipment I would use when, a series of progressive exposures for totality, and so forth.

And then, a couple of days before we were due to leave, I figured I should test my rig -- and discovered that it was basically impossible to focus on the sun. For the Venus transit, the sun wasn't that high in the sky, so I focused through the viewfinder. But for the total eclipse, the sun would be almost overhead, and the viewfinder nearly impossible to see. So I had planned to point the Mak at a distant hillside, focus it, then slip the filter on and point it up to the sun. It turned out the focal point was completely different through the filter.

[Solar finder for DSLR, made from popsicle sticks] With only a couple of days left to go, I revised my plan. The Mak is difficult to focus under any circumstances. I decided not to use it, and to stick to my Canon 55-250mm zoom telephoto, with the camera on a normal tripod. I'd skip the partial eclipse (I've photographed those before anyway) and concentrate on getting a few shots of the diamond ring and the corona, running through a range of exposures without needing to look at the camera screen or do any refocusing. And since I wasn't going to be usinga telescope, my nifty solar finders wouldn't work; I designed a new one out of popsicle sticks to fit in the camera's hot shoe.

Getting there

We stayed with relatives in Colorado Saturday night, then drove to Laramie Sunday. I'd heard horror stories of hotels canceling people's longstanding eclipse reservations, but fortunately our hotel honored our reservation. WHEW! Monday morning, we left the hotel at 6am in case we hit terrible traffic. There was already plenty of traffic on the highway north to Casper, but we turned east hoping for fewer crowds. A roadsign sign said "NO PARKING ON HIGHWAY." They'd better not try to enforce that in the totality zone!

[Our eclipse viewing pullout on Wyoming 270] When we got to I-25 it was moving and, oddly enough, not particularly crowded. Glendo Reservoir had looked on the map like a nice spot on the centerline ... but it was also a state park, so there was a risk that everyone else would want to go there. Sure enough: although traffic was moving on I-25 at Wheatland, a few miles north the freeway came to a screeching halt. We backtracked and headed east toward Guernsey, where several highways went north toward the centerline.

East of Glendo, there were crowds at every highway pullout and rest stop. As we turned onto 270 and started north, I kept an eye on OsmAnd on my phone, where I'd loaded a GPX file of the eclipse path. When we were within a mile of the centerline, we stopped at a likely looking pullout. It was maybe 9 am. A cool wind was blowing -- very pleasant since we were expecting a hot day -- and we got acquainted with our fellow eclipse watchers as we waited for first contact.

Our pullout was also the beginning of a driveway to a farmhouse we could see in the distance. Periodically people pulled up, looking lost, checked maps or GPS, then headed down the road to the farm. Apparently the owners had advertised it as an eclipse spot -- pay $35, and you can see the eclipse and have access to a restroom too! But apparently the old farmhouse's plumbing failed early on, and some of the people who'd paid came out to the road to watch with us since we had better equipment set up.

[Terrible afocal view of partial eclipse] There's not much to say about the partial eclipse. We all traded views -- there were five or six scopes at our pullout, including a nice little H-alpha scope. I snapped an occasional photo through the 80mm with my pocket camera held to the eyepiece, or with the DSLR through an eyepiece projection adapter. Oddly, the DSLR photos came out worse than the pocket cam ones. I guess I should try and debug that at some point.

Shortly before totality, I set up the DSLR on the tripod, focused on a distant hillside and taped the focus with duct tape, plugged in the shutter remote, checked the settings in Manual mode, then set the camera to Program mode and AEB (auto exposure bracketing). I put the lens cap back on and pointed the camera toward the sun using the popsicle-stick solar finder. I also set a countdown timer, so I could press START when totality began and it would beep to warn me when it was time to the sun to come back out. It was getting chilly by then, with the sun down to a sliver, and we put on sweaters.

The pair of eclipse veterans at our pullout had told everybody to watch for the moon's shadow racing toward us across the hills from the west. But I didn't see the racing shadow, nor any shadow bands.

And then Venus and Mercury appeared and the sun went away.

Totality

[Solar eclipse diamond ring] One thing the photos don't prepare you for is the color of the sky. I expected it would look like twilight, maybe a little darker; but it was an eerie, beautiful medium slate blue. With that unworldly solar corona in the middle of it, and Venus gleaming as bright as you've ever seen it, and Mercury shining bright on the other side. There weren't many stars.

We didn't see birds doing anything unusual; as far as I can tell, there are no birds in this part of Wyoming. But the cows did all get in a line and start walking somewhere. Or so Dave tells me. I wasn't looking at the cows.

Amazingly, I remembered to start my timer and to pull off the DSLR's lens cap as I pushed the shutter button for the diamond-ring shots without taking my eyes off the spectacle high above. I turned the camera off and back on (to cancel AEB), switched to M mode, and snapped a photo while I scuttled over to the telescope, pulled the filter off and took a look at the corona in the wide-field eyepiece. So beautiful! Binoculars, telescope, naked eye -- I don't know which view was best.

I went through my exposure sequence on the camera, turning the dial a couple of clicks each time without looking at the settings, keeping my eyes on the sky or the telescope eyepiece. But at some point I happened to glance at the viewfinder -- and discovered that the sun was drifting out of the frame. Adjusting the tripod to get it back in the frame took longer than I wanted, but I got it there and got my eyes back on the sun as I snapped another photo ...

and my timer beeped.

I must have set it wrong! It couldn't possibly have been two and a half minutes. It had been 30, 45 seconds tops.

But I nudged the telescope away from the sun, and looked back up -- to another diamond ring. Totality really was ending and it was time to stop looking.

Getting Out

The trip back to Golden, where we were staying with a relative, was hellish. We packed up immediately after totality -- we figured we'd seen partials before, and maybe everybody else would stay. No such luck. By the time we got all the equipment packed there was already a steady stream of cars heading south on 270.

A few miles north of Guernsey the traffic came to a stop. This was to be the theme of the afternoon. Every small town in Wyoming has a stop sign or signal, and that caused backups for miles in both directions. We headed east, away from Denver, to take rural roads down through eastern Wyoming and Colorado rather than I-25, but even so, we hit small-town stop sign backups every five or ten miles.

We'd brought the Rav4 partly for this reason. I kept my eyes glued on OsmAnd and we took dirt roads when we could, skirting the paved highways -- but mostly there weren't any dirt roads going where we needed to go. It took about 7 hours to get back to Golden, about twice as long as it should have taken. And we should probably count ourselves lucky -- I've heard from other people who took 11 hours to get to Denver via other routes.

Lessons Learned

Dave is fond of the quote, "No battle plan survives contact with the enemy" (which turns out to be from Prussian military strategist Helmuth von Moltke the Elder).

The enemy, in this case, isn't the eclipse; it's time. Two and a half minutes sounds like a lot, but it goes by like nothing.

Even in my drastically scaled-down plan, I had intended exposures from 1/2000 to 2 seconds (at f/5.6 and ISO 400). In practice, I only made it to 1/320 because of fiddling with the tripod.

And that's okay. I'm thrilled with the photos I got, and definitely wouldn't have traded any eyeball time for more photos. I'm more annoyed that the tripod fiddling time made me miss a little bit of extra looking. My script actually worked out better than I expected, and I was very glad I'd done the preparation I had. The script was reasonable, the solar finders worked really well, and the lens was even in focus for the totality shots.

Then there's the eclipse itself.

I've read so many articles about solar eclipses as a mystical, religious experience. It wasn't, for me. It was just an eerily beautiful, other-worldly spectacle: that ring of cold fire staring down from the slate blue sky, bright planets but no stars, everything strange, like nothing I'd ever seen. Photos don't get across what it's like to be standing there under that weird thing in the sky.

I'm not going to drop everything to become a globe-trotting eclipse chaser ... but I sure hope I get to see another one some day.

Photos: 2017 August 21 Total Solar Eclipse in Wyoming.

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[ 20:41 Aug 27, 2017    More science/astro | permalink to this entry | ]

Mon, 14 Aug 2017

A Homemade Solar Finder, for the Eclipse

While I was testing various attempts at motorizing my barn-door mount, trying to get it to track the sun, I had to repeatedly find the sun in my telescope.

In the past, I've generally used the shadow of the telescope combined with the shadow of the finderscope. That works, more or less, but it's not ideal: it doesn't work as well with just a telescope with no finder, which includes both of the scopes I'm planning to take to the eclipse; and it requires fairly level ground under the telescope: it doesn't work if there are bushes or benches in the way of the shadow.

For the eclipse, I don't want to waste any time finding the sun: I want everything as efficient as possible. I decided to make a little solar finderscope. One complication, though: since I don't do solar observing very often, I didn't want to use tape, glue or, worse, drill holes to mount it.

So I wanted something that could be pressed against the telescope and held there with straps or rubber bands, coming off again without leaving a mark. A length of an angled metal from my scrap pile seemed like a good size to be able to align itself against a small telescope tube.

[Constructing a solar sight] Then I needed front and rear sights. For the front sight, I wanted a little circle that could project a bulls-eye shadow onto a paper card attached to the rear sight. I looked at the hardware store for small eye-bolts, but no dice. Apparently they don't come that small.I settled for the second-smallest size of screw eye.

The screw eye, alas, is meant to screw into wood, not metal. So I cut a short strip of wood a reasonable size to nestle into the inside of the angle-iron. (That ripsaw Dave bought last year sure does come in handy sometimes.) I drilled some appropriately sized holes and fastened screw eyes on both ends, adding a couple of rubber grommets as spacers because the screw eyes were a little too long and I didn't want the pointy ends of the screws getting near my telescope tube.

I added some masking tape on the sides of the angle iron so it wouldn't rub off the paint on the telescope tube, then bolted a piece of cardboard cut from an old business card to the rear screw eye.

[Homemade solar sight] Voila! A rubber-band-attached solar sight that took about an hour to make. Notice how the shadow of the front sight exactly fits around the rear sight: you line up the shadow with the rear sight to point the scope. It seems to work pretty well, and it should be adaptable to any telescope I use.

I used a wing nut to attach the rear cardboard: that makes it easy to replace it or remove it. With the cardboard removed, the sight might even work for night-time astronomy viewing. That is, it does work, as long as there's enough ambient light to see the rings. Hmm... maybe I should paint the rings with glow-in-the-dark paint.

Update: I have an even simpler design that works perfectly on a camera with a hot shoe, and almost as well on a telescope, pictured here: Camera solar finder made from popsicle sticks.

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[ 15:25 Aug 14, 2017    More science/astro | permalink to this entry | ]

Thu, 10 Aug 2017

A Barn-Door Mount for the Eclipse

[Curved rod barn-door mount] I've been meaning forever to try making a "barn door" tracking mount. Used mainly for long-exposure wide-field astrophotography, the barn door mount, invented in 1975, is basically two pieces of wood with a hinge. The bottom board mounts on a tripod and is pointed toward the North Star; "opening" the hinge causes the top board to follow the motion of the sky, like an equatorial telescope mount. A threaded rod and a nut control the angle of the "door", and you turn the nut manually every so often. Of course, you can also drive it with a motor.

We're off to view the eclipse in a couple of weeks. Since it's my first total eclipse, my plan is to de-emphasize photography: especially during totality, I want to experience the eclipse, not miss it because my eyes are glued to cameras and timers and other equipment. But I still want to take photos every so often. Constantly adjusting a tripod to keep the sun in frame is another hassle that might keep my attention away from the eclipse. But real equatorial mounts are heavy and a time consuming to set up; since I don't know how crowded the area will be, I wasn't planning to take one. Maybe a barn door would solve that problem.

Perhaps more useful, it would mean that my sun photos would all be rotated approximately the right amount, in case I wanted to make an animation. I've taken photos of lunar and partial solar eclipses, but stringing them together into an animation turned out to be too much hassle because of the need to rotate and position each image.

I've known about barn-door mounts since I was a kid, and I knew the basic theory, but I'd never paid much attention to the details. When I searched the web, it sounded complicated -- it turned out there are many types that require completely different construction techniques.

The best place to start (I found out after wasting a lot of time on other sites) is the Wikipedia article on "Barn door tracker", which gives a wonderfully clear overview, with photos, of the various types. I had originally been planning a simple tangent or isosceles type; but when I read construction articles, it seemed that those seemingly simple types might not be so simple to build: the angle between the threaded rod and the boards is always changing, so you need some kind of a pivot. Designing the pivot looked tricky. Meanwhile, the pages I found on curved-rod mounts all insisted that bending the rod was easy, no trouble at all. I decided to try a curved-rod mount first.

The canonical reference is a 2015 article by Gary Seronik: A Tracking Platform for Astrophotography. But I found three other good construction guides: Optical Ed's "Making a Curve Bolt Barn Door", a Cloudy Nights discussion thread "Motorized Barn Door Mount Kit", and Massapoag Pond Photography's "Barn Door Tracker". I'm not going to reprise all their construction details, so refer to those sites if you try making your own mount.

[Barn-door mount, showing piano hinge] The crucial parts are a "piano hinge", a long hinge that eliminates the need to line up two or more hinges, and the threaded rod. Buying a piano hinge in the right size proved impossible locally, but the folks at Metzger's assured me that piano hinges can be cut, so I bought one longer than I needed and cut it to size. I used a 1/4-20 rod, which meant (per the discussions in the Cloudy Nights discussion linked above) that a 11.43-inch radius from the hinge to the holes the rod passes through would call for the nut to turn at a nice round number of 1 RPM.

I was suspicious of the whole "it's easy to bend the threaded rod ina 11.43-inch circle" theory, but it turned out to be true. Draw the circle you want on a sheet of newspaper, put on some heavy gloves and start bending, frequently comparing your rod to the circle you drew. You can fine-tune the curvature later.

I cut my boards, attached the hinge, measured about 11.4" and drilled a hole for the threaded rod. The hole needed to be a bit bigger than 5/8" to let the curved rod pass through without rubbing. Attach the curved rod to the top wood piece with a couple of nuts and some washers, and then you can fine-tune the rod's curvature, opening and closing the hinge and re-bending the rod a little in any place it rubs.

A 5/8" captive nut on the top piece lets you attach a tripod head which will hold your camera or telescope. A 1/4" captive nut on the bottom piece serves to attach the mount to a tripod -- you need a 1/4", not 3/8": the rig needs to mount on a tripod head, not just the legs, so you can align the hinge to the North Star. (Of course, you could build a wedge or your own set of legs, if you prefer.) The 3/4" plywood I was using turned out to be thicker than the captive nuts, so I had to sand the wood thinner in both places. Maybe using half-inch plywood would have been better.

[Wing nut on barn-door mount] The final piece is the knob/nut you'll turn to make the mount track. I couldn't find a good 1/4" knob for under $15. A lot of people make a wood circle and mount the nut in the center, or use a gear so a motor can drive the mount. I looked around at things like jam-jar lids and the pile of metal gears and sprinkler handles in my welding junkpile, but I didn't see anything that looked quite right, so I decided to try a wing nut just for testing, and worry about the knob later. Turns out a wing nut works wonderfully; there's no particular need for anything else if you're driving your barn-door manually.

Testing time! I can't see Polaris from my deck, and I was too lazy to set up anywhere else, so I used a protractor to set the hinge angle to roughly 36° (my latitude), then pointed it approximately north. I screwed my Pro-Optic 90mm Maksutov (the scope I plan to use for my eclipse photos) onto the ball head and pointed it at the moon as soon as it rose. With a low power eyepiece (20x), turning the wing nut kept the moon more or less centered in the field for the next half-hour, until clouds covered the moon and rain began threatening. I didn't keep track of how many turns I was making, since I knew the weather wasn't going to allow a long session, and right now I'm not targeting long-exposure photography, just an easy way of keeping an object in view.

A good initial test! My web searches, and the discovery of all those different types of barn-door mounts and pivots and flex couplings and other scary terms, had seemed initially daunting. But in the end, building a barn-door mount was just as easy as people say it is, and I finished it in a day.

And what about a motor? I added one a few days later, with a stepper and an Arduino. But that's a separate article.

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[ 19:25 Aug 10, 2017    More science/astro | permalink to this entry | ]

Fri, 05 May 2017

Moon Talk at PEEC tonight

Late notice, but Dave and I are giving a talk on the moon tonight at PEEC. It's called Moonlight Sonata, and starts at 7pm. Admission: $6/adult, $4/child (we both prefer giving free talks, but PEEC likes to charge for their Friday planetarium shows, and it all goes to support PEEC, a good cause).

We'll bring a small telescope in case anyone wants to do any actual lunar observing outside afterward, though usually planetarium audiences don't seem very interested in that.

If you're local but can't make it this time, don't worry; the moon isn't a one-time event, so I'm sure we'll give the moon show again at some point.

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[ 15:26 May 05, 2017    More speaking | permalink to this entry | ]

Sat, 18 Jun 2016

Cave 6" as a Quick-Look Scope

I haven't had a chance to do much astronomy since moving to New Mexico, despite the stunning dark skies. For one thing, those stunning dark skies are often covered with clouds -- New Mexico's dramatic skyscapes can go from clear to windy to cloudy to hail or thunderstorms and back to clear and hot over the course of a few hours. Gorgeous to watch, but distracting for astronomy, and particularly bad if you want to plan ahead and observe on a particular night. The Pajarito Astronomers' monthly star parties are often clouded or rained out, as was the PEEC Nature Center's moon-and-planets star party last week.

That sort of uncertainty means that the best bet is a so-called "quick-look scope": one that sits by the door, ready to be hauled out if the sky is clear and you have the urge. Usually that means some kind of tiny refractor; but it can also mean leaving a heavy mount permanently set up (with a cover to protect it from those thunderstorms) so it's easy to carry out a telescope tube and plunk it on the mount.

I have just that sort of scope sitting in our shed: an old, dusty Cave Astrola 6" Newtonian on an equatorian mount. My father got it for me on my 12th birthday. Where he got the money for such a princely gift -- we didn't have much in those days -- I never knew, but I cherished that telescope, and for years spent most of my nights in the backyard peering through the Los Angeles smog.

Eventually I hooked up with older astronomers (alas, my father had passed away) and cadged rides to star parties out in the Mojave desert. Fortunately for me, parenting standards back then allowed a lot more freedom, and my mother was a good judge of character and let me go. I wonder if there are any parents today who would let their daughter go off to the desert with a bunch of strange men? Even back then, she told me later, some of her friends ribbed her -- "Oh, 'astronomy'. Suuuuuure. They're probably all off doing drugs in the desert." I'm so lucky that my mom trusted me (and her own sense of the guys in the local astronomy club) more than her friends.

The Cave has followed me through quite a few moves, heavy, bulky and old fashioned as it is; even when I had scopes that were bigger, or more portable, I kept it for the sentimental value. But I hadn't actually set it up in years. Last week, I assembled the heavy mount and set it up on a clear spot in the yard. I dusted off the scope, cleaned the primary mirror and collimated everything, replaced the finder which had fallen out somewhere along the way, set it up ... and waited for a break in the clouds.

[Hyginus Rille by Michael Karrer] I'm happy to say that the optics are still excellent. As I write this (to be posted later), I just came in from beautiful views of Hyginus Rille and the Alpine Valley on the moon. On Jupiter the Great Red Spot was just rotating out. Mars, a couple of weeks before opposition, is still behind a cloud (yes, there are plenty of clouds). And now the clouds have covered the moon and Jupiter as well. Meanwhile, while I wait for a clear view of Mars, a bat makes frenetic passes overhead, and something in the junipers next to my observing spot is making rhythmic crunch, crunch, crunch sounds. A rabbit chewing something tough? Or just something rustling in the bushes?

I just went out again, and now the clouds have briefly uncovered Mars. It's the first good look I've had at the Red Planet in years. (Tiny achromatic refractors really don't do justice to tiny, bright objects.) Mars is the most difficult planet to observe: Dave liks to talk about needing to get your "Mars eyes" trained for each Mars opposition, since they only come every two years. But even without my "Mars eyes", I had no trouble seeing the North pole with dark Acidalia enveloping it, and, in the south, the sinuous chain of Sini Sabaeus, Meridiani, Margaritifer, and Mare Erythraeum. (I didn't identify any of these at the time; instead, I dusted off my sketch pad and sketched what I saw, then compared it with XEphem's Mars view afterward.)

I'm liking this new quick-look telescope -- not to mention the childhood memories it brings back.

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[ 08:53 Jun 18, 2016    More science/astro | permalink to this entry | ]

Sun, 04 Oct 2015

Aligning images to make an animation (or an image stack)

For the animations I made from the lunar eclipse last week, the hard part was aligning all the images so the moon (or, in the case of the moonrise image, the hillside) was in the same position in every time.

This is a problem that comes up a lot with astrophotography, where multiple images are stacked for a variety of reasons: to increase contrast, to increase detail, or to take an average of a series of images, as well as animations like I was making this time. And of course animations can be fun in any context, not just astrophotography.

In the tutorial that follows, clicking on the images will show a full sized screenshot with more detail.

Load all the images as layers in a single GIMP image

The first thing I did was load up all the images as layers in a single image: File->Open as Layers..., then navigate to where the images are and use shift-click to select all the filenames I wanted.

[Upper layer 50% opaque to align two layers]

Work on two layers at once

By clicking on the "eyeball" icon in the Layers dialog, I could adjust which layers were visible. For each pair of layers, I made the top layer about 50% opaque by dragging the opacity slider (it's not important that it be exactly at 50%, as long as you can see both images).

Then use the Move tool to drag the top image on top of the bottom image.
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But it's hard to tell when they're exactly aligned

"Drag the top image on top of the bottom image": easy to say, hard to do. When the images are dim and red like that, and half of the image is nearly invisible, it's very hard to tell when they're exactly aligned.

[]

Use a Contrast display filter

What helped was a Contrast filter. View->Display Filters... and in the dialog that pops up, click on Contrast, and click on the right arrow to move it to Active Filters.

The Contrast filter changes the colors so that dim red moon is fully visible, and it's much easier to tell when the layers are approximately on top of each other.

[]

Use Difference mode for the final fine-tuning

Even with the Contrast filter, though, it's hard to see when the images are exactly on top of each other. When you have them within a few pixels, get rid of the contrast filter (you can keep the dialog up but disable the filter by un-checking its checkbox in Active Filters). Then, in the Layers dialog, slide the top layer's Opacity back to 100%, go to the Mode selector and set the layer's mode to Difference.

In Difference mode, you only see differences between the two layers. So if your alignment is off by a few pixels, it'll be much easier to see. Even in a case like an eclipse where the moon's appearance is changing from frame to frame as the earth's shadow moves across it, you can still get the best alignment by making the Difference between the two layers as small as you can.

Use the Move tool and the keyboard: left, right, up and down arrows move your layer by one pixel at a time. Pick a direction, hit the arrow key a couple of times and see how the difference changes. If it got bigger, use the opposite arrow key to go back the other way.

When you get to where there's almost no difference between the two layers, you're done. Change Mode back to Normal, make sure Opacity is at 100%, then move on to the next layer in the stack.

It's still a lot of work. I'd love to find a program that looks for circular or partially-circular shapes in successive images and does the alignment automatically. Someone on GIMP suggested I might be able to write something using OpenCV, which has circle-finding primitives (I've written briefly before about SimpleCV, a wrapper that makes OpenCV easy to use from Python). But doing the alignment by hand in GIMP, while somewhat tedious, didn't take as long as I expected once I got the hang of using the Contrast display filter along with Opacity and Difference mode.

Creating the animation

Once you have your layers, how do you turn them into an animation?

The obvious solution, which I originally intended to use, is to save as GIF and check the "animated" box. I tried that -- and discovered that the color errors you get when converting an image to indexed make a beautiful red lunar eclipse look absolutely awful.

So I threw together a Javascript script to animate images by loading a series of JPEGs. That meant that I needed to export all the layers from my GIMP image to separate JPG files.

GIMP doesn't have a built-in way to export all of an image's layers to separate new images. But that's an easy plug-in to write, and a web search found lots of plug-ins already written to do that job.

The one I ended up using was Lie Ryan's Python script in How to save different layers of a design in separate files; though a couple of others looked promising (I didn't try them), such as gimp-plugin-export-layers and save_all_layers.scm.

You can see the final animation here: Lunar eclipse of September 27, 2015: Animations.

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[ 09:44 Oct 04, 2015    More gimp | permalink to this entry | ]

Thu, 01 Oct 2015

Lunar eclipse animations

[Eclipsed moon rising] The lunar eclipse on Sunday was gorgeous. The moon rose already in eclipse, and was high in the sky by the time totality turned the moon a nice satisfying deep red.

I took my usual slipshod approach to astrophotography. I had my 90mm f/5.6 Maksutov lens set up on the patio with the camera attached, and I made a shot whenever it seemed like things had changed significantly, adjusting the exposure if the review image looked like it might be under- or overexposed, occasionally attempting to refocus. The rest of the time I spent socializing with friends, trading views through other telescopes and binoculars, and enjoying an apple tart a la mode.

So the images I ended up with aren't all they could be -- not as sharply focused as I'd like (I never have figured out a good way of focusing the Rebel on astronomy images) and rather grainy.

Still, I took enough images to be able to put together a couple of animations: one of the lovely moonrise over the mountains, and one of the sequence of the eclipse through totality.

Since the 90mm Mak was on a fixed tripod, the moon drifted through the field and I had to adjust it periodically as it drifted out. So the main trick to making animations was aligning all the moon images. I haven't found an automated way of doing that, alas, but I did come up with some useful GIMP techniques, which I'm in the process of writing up as a tutorial.

Once I got the images all aligned as layers in a GIMP image, I saved them as an animated GIF -- and immediately discovered that the color error you get when converting to an indexed GIF image loses all the beauty of those red colors. Ick!

So instead, I wrote a little Javascript animation function that loads images one by one at fixed intervals. That worked a lot better than the GIF animation, plus it lets me add a Start/Stop button.

You can view the animations (or the source for the javascript animation function) here: Lunar eclipse animations

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[ 12:55 Oct 01, 2015    More science/astro | permalink to this entry | ]

Mon, 21 Sep 2015

The meaning of "fetid"; Albireo; and musings on variations in sensory perception

[Fetid marigold, which actually smells wonderfully minty] The street for a substantial radius around my mailbox has a wonderful, strong minty smell. The smell is coming from a clump of modest little yellow flowers.

They're apparently Dyssodia papposa, whose common name is "fetid marigold". It's in the sunflower family, Asteraceae, not related to Lamiaceae, the mints.

"Fetid", of course, means "Having an offensive smell; stinking". When I google for fetid marigold, I find quotes like "This plant is so abundant, and exhales an odor so unpleasant as to sicken the traveler over the western prairies of Illinois, in autumn." And nobody says it smells like mint -- at least, googling for the plant and "mint" or "minty" gets nothing.

But Dave and I both find the smell very minty and pleasant, and so do most of the other local people I queried. What's going on?

[Fetid goosefoot] Another local plant which turns strikingly red in autumn has an even worse name: fetid goosefoot. On a recent hike, several of us made a point of smelling it. Sure enough: everybody except one found it minty and pleasant. But one person on the hike said "Eeeeew!"

It's amazing how people's sensory perception can vary. Everybody knows how people's taste varies: some people perceive broccoli and cabbage as bitter while others love the taste. Some people can't taste lobster and crab at all and find Parmesan cheese unpleasant.

And then there's color vision. Every amateur astronomer who's worked public star parties knows about Albireo. Also known as beta Cygni, Albireo is a double star, the head of the constellation of the swan or the foot of the Northern Cross. In a telescope, it's a double star, and a special type of double: what's known as a "color double", two stars which are very different colors from each other.

Most non-astronomers probably don't think of stars having colors. Mostly, color isn't obvious when you're looking at things at night: you're using your rods, the cells in your retina that are sensitive to dim light, not your cones, which provide color vision but need a fair amount of light to work right.

But when you have two things right next to each other that are different colors, the contrast becomes more obvious. Sort of.

[Albireo, from Jefffisher10 on Wikimedia Commons] Point a telescope at Albireo at a public star party and ask the next ten people what two colors they see. You'll get at least six, more likely eight, different answers. I've heard blue and red, blue and gold, red and gold, red and white, pink and blue ... and white and white (some people can't see the colors at all).

Officially, the bright component is actually a close binary, too close to resolve as separate stars. The components are Aa (magnitude 3.18, spectral type K2II) and Ac (magnitude 5.82, spectral type B8). (There doesn't seem to be an Albireo Ab.) Officially that makes Albireo A's combined color yellow or amber. The dimmer component, Albireo B, is magnitude 5.09 and spectral type B8Ve: officially it's blue.

But that doesn't make the rest of the observers wrong. Color vision is a funny thing, and it's a lot more individual than most people think. Especially in dim light, at the limits of perception. I'm sure I'll continue to ask that question when I show Albireo in my telescope, fascinated with the range of answers.

In case you're wondering, I see Albireo's components as salmon-pink and pale blue. I enjoy broccoli and lobster but find bell peppers bitter. And I love the minty smell of plants that a few people, apparently, find "fetid".

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[ 16:09 Sep 21, 2015    More nature | permalink to this entry | ]

Thu, 10 Sep 2015

The blooms of summer, and weeds that aren't weeds

[Wildflowers on the Quemazon trail] One of the adjustments we've had to make in moving to New Mexico is getting used to the backward (compared to California) weather. Like, rain in summer!

Not only is rain much more pleasant in summer, as a dramatic thundershower that cools you off on a hot day instead of a constant cold drizzle in winter (yes, I know that by now Calfornians need a lot more of that cold drizzle! But it's still not very pleasant being out in it). Summer rain has another unexpected effect: flowers all summer, a constantly changing series of them.

Right now the purple asters are just starting up, while skyrocket gilia and the last of the red penstemons add a note of scarlet to a huge array of yellow flowers of all shapes and sizes. Here's the vista that greeted us on a hike last weekend on the Quemazon trail.

Down in the piñon-juniper where we live, things aren't usually quite so colorful; we lack many red blooms, though we have just as many purple asters as they do up on the hill, plus lots of pale trumpets (a lovely pale violet gilia) and Cowpen daisy, a type of yellow sunflower.

But the real surprise is a plant with a modest name: snakeweed. It has other names, but they're no better: matchbrush, broomweed. It grows everywhere, and most of the year it just looks like a clump of bunchgrass.

[Snakeweed in bloom] Then come September, especially in a rainy year like this one, and all that snakeweed suddenly bursts into a glorious carpet of gold.

We have plenty of other weeds -- learning how to identify Russian thistle (tumbleweed), kochia and amaranth when they're young, so we can pull them up before they go to seed and spread farther, has launched me on a project of an Invasive Plants page for the nature center (we should be ready to make that public soon).

But snakeweed, despite the name, is a welcome guest in our yard, and it lifts my spirits to walk through it on a September evening.

By the way, if anyone in Los Alamos reads this blog, Dave and I are giving our first planetarium show at the nature center tomorrow (that's Friday) afternoon. Unlike most PEEC planetarium shows, it's free! Which is probably just as well since it's our debut. If you want to come see us, the info is here: Night Sky Fiesta Planetarium Show.

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[ 21:24 Sep 10, 2015    More nature | permalink to this entry | ]

Fri, 24 Oct 2014

Partial solar eclipse, with amazing sunspots

[Partial solar eclipse, with sunspots] We had perfect weather for the partial solar eclipse yesterday. I invited some friends over for an eclipse party -- we set up a couple of scopes with solar filters, put out food and drink and had an enjoyable afternoon.

And what views! The sunspot group right on the center of the sun's disk was the most large and complex I'd ever seen, and there were some much smaller, more subtle spots in the path of the eclipse. Meanwhile, the moon's limb gave us a nice show of mountains and crater rims silhouetted against the sun.

I didn't do much photography, but I did hold the point-and-shoot up to the eyepiece for a few shots about twenty minutes before maximum eclipse, and was quite pleased with the result.

An excellent afternoon. And I made too much blueberry bread and far too many oatmeal cookies ... so I'll have sweet eclipse memories for quite some time.

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[ 09:15 Oct 24, 2014    More science/astro | permalink to this entry | ]

Thu, 31 Jul 2014

Predicting planetary visibility with PyEphem

Part II: Predicting Conjunctions

After I'd written a basic script to calculate when planets will be visible, the next step was predicting conjunctions, times when two or more planets are close together in the sky.

Finding separation between two objects is easy in PyEphem: it's just one line once you've set up your objects, observer and date.

p1 = ephem.Mars()
p2 = ephem.Jupiter()
observer = ephem.Observer()  # and then set it to your city, etc.
observer.date = ephem.date('2014/8/1')
p1.compute(observer)
p2.compute(observer)

ephem.separation(p1, p2)

So all I have to do is loop over all the visible planets and see when the separation is less than some set minimum, like 4 degrees, right?

Well, not really. That tells me if there's a conjunction between a particular pair of planets, like Mars and Jupiter. But the really interesting events are when you have three or more objects close together in the sky. And events like that often span several days. If there's a conjunction of Mars, Venus, and the moon, I don't want to print something awful like

Friday:
  Conjunction between Mars and Venus, separation 2.7 degrees.
  Conjunction between the moon and Mars, separation 3.8 degrees.
Saturday:
  Conjunction between Mars and Venus, separation 2.2 degrees.
  Conjunction between Venus and the moon, separation 3.9 degrees.
  Conjunction between the moon and Mars, separation 3.2 degrees.
Sunday:
  Conjunction between Venus and the moon, separation 4.0 degrees.
  Conjunction between the moon and Mars, separation 2.5 degrees.

... and so on, for each day. I'd prefer something like:

Conjunction between Mars, Venus and the moon lasts from Friday through Sunday.
  Mars and Venus are closest on Saturday (2.2 degrees).
  The moon and Mars are closest on Sunday (2.5 degrees).

At first I tried just keeping a list of planets involved in the conjunction. So if I see Mars and Jupiter close together, I'd make a list [mars, jupiter], and then if I see Venus and Mars on the same date, I search through all the current conjunction lists and see if either Venus or Mars is already in a list, and if so, add the other one. But that got out of hand quickly. What if my conjunction list looks like [ [mars, venus], [jupiter, saturn] ] and then I see there's also a conjunction between Mars and Jupiter? Oops -- how do you merge those two lists together?

The solution to taking all these pairs and turning them into a list of groups that are all connected actually lies in graph theory: each conjunction pair, like [mars, venus], is an edge, and the trick is to find all the connected edges. But turning my list of conjunction pairs into a graph so I could use a pre-made graph theory algorithm looked like it was going to be more code -- and a lot harder to read and less maintainable -- than making a bunch of custom Python classes.

I eventually ended up with three classes: ConjunctionPair, for a single conjunction observed between two bodies on a single date; Conjunction, a collection of ConjunctionPairs covering as many bodies and dates as needed; and ConjunctionList, the list of all Conjunctions currently active. That let me write methods to handle merging multiple conjunction events together if they turned out to be connected, as well as a method to summarize the event in a nice, readable way.

So predicting conjunctions ended up being a lot more code than I expected -- but only because of the problem of presenting it neatly to the user. As always, user interface represents the hardest part of coding.

The working script is on github at conjunctions.py.

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[ 19:57 Jul 31, 2014    More science/astro | permalink to this entry | ]

Wed, 23 Jul 2014

Predicting planetary visibility with PyEphem

Part 1: Basic Planetary Visibility

All through the years I was writing the planet observing column for the San Jose Astronomical Association, I was annoyed at the lack of places to go to find out about upcoming events like conjunctions, when two or more planets are close together in the sky. It's easy to find out about conjunctions in the next month, but not so easy to find sites that will tell you several months in advance, like you need if you're writing for a print publication (even a club newsletter).

For some reason I never thought about trying to calculate it myself. I just assumed it would be hard, and wanted a source that could spoon-feed me the predictions.

The best source I know of is the RASC Observer's Handbook, which I faithfully bought every year and checked each month so I could enter that month's events by hand. Except for January and February, when I didn't have the next year's handbook yet by the time my column went to press and I was on my own. I have to confess, I was happy to get away from that aspect of the column when I moved.

In my new town, I've been helping the local nature center with their website. They had some great pages already, like a What's Blooming Now? page that keeps track of which flowers are blooming now and only shows the current ones. I've been helping them extend it by adding features like showing only flowers of a particular color, separating the data into CSV databases so it's easier to add new flowers or butterflies, and so forth. Eventually we hope to build similar databases of birds, reptiles and amphibians.

And recently someone suggested that their astronomy page could use some help. Indeed it could -- it hadn't been updated in about five years. So we got to work looking for a source of upcoming astronomy events we could use as a data source for the page, and we found sources for a few things, like moon phases and eclipses, but not much.

Someone asked about planetary conjunctions, and remembering how I'd always struggled to find that data, especially in months when I didn't have the RASC handbook yet, I got to wondering about calculating it myself. Obviously it's possible to calculate when a planet will be visible, or whether two planets are close to each other in the sky. And I've done some programming with PyEphem before, and found it fairly easy to use. How hard could it be?

Note: this article covers only the basic problem of predicting when a planet will be visible in the evening. A followup article will discuss the harder problem of conjunctions.

Calculating planet visibility with PyEphem

The first step was figuring out when planets were up. That was straightforward. Make a list of the easily visible planets (remember, this is for a nature center, so people using the page aren't expected to have telescopes):

import ephem

planets = [
    ephem.Moon(),
    ephem.Mercury(),
    ephem.Venus(),
    ephem.Mars(),
    ephem.Jupiter(),
    ephem.Saturn()
    ]

Then we need an observer with the right latitude, longitude and elevation. Elevation is apparently in meters, though they never bother to mention that in the PyEphem documentation:

observer = ephem.Observer()
observer.name = "Los Alamos"
observer.lon = '-106.2978'
observer.lat = '35.8911'
observer.elevation = 2286  # meters, though the docs don't actually say

Then we loop over the date range for which we want predictions. For a given date d, we're going to need to know the time of sunset, because we want to know which planets will still be up after nightfall.

observer.date = d
sunset = observer.previous_setting(sun)

Then we need to loop over planets and figure out which ones are visible. It seems like a reasonable first approach to declare that any planet that's visible after sunset and before midnight is worth mentioning.

Now, PyEphem can tell you directly the rising and setting times of a planet on a given day. But I found it simplified the code if I just checked the planet's altitude at sunset and again at midnight. If either one of them is "high enough", then the planet is visible that night. (Fortunately, here in the mid latitudes we don't have to worry that a planet will rise after sunset and then set again before midnight. If we were closer to the arctic or antarctic circles, that would be a concern in some seasons.)

min_alt = 10. * math.pi / 180.
for planet in planets:
    observer.date = sunset
    planet.compute(observer)
    if planet.alt > min_alt:
        print planet.name, "is already up at sunset"

Easy enough for sunset. But how do we set the date to midnight on that same night? That turns out to be a bit tricky with PyEphem's date class. Here's what I came up with:

    midnight = list(observer.date.tuple())
    midnight[3:6] = [7, 0, 0]
    observer.date = ephem.date(tuple(midnight))
    planet.compute(observer)
    if planet.alt > min_alt:
        print planet.name, "will rise before midnight"

What's that 7 there? That's Greenwich Mean Time when it's midnight in our time zone. It's hardwired because this is for a web site meant for locals. Obviously, for a more general program, you should get the time zone from the computer and add accordingly, and you should also be smarter about daylight savings time and such. The PyEphem documentation, fortunately, gives you tips on how to deal with time zones. (In practice, though, the rise and set times of planets on a given day doesn't change much with time zone.)

And now you have your predictions of which planets will be visible on a given date. The rest is just a matter of writing it out into your chosen database format.

In the next article, I'll cover planetary and lunar conjunctions -- which were superficially very simple, but turned out to have some tricks that made the programming harder than I expected.

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[ 21:32 Jul 23, 2014    More science/astro | permalink to this entry | ]

Sat, 07 Sep 2013

Daytime Venus-Moon-Saturn conjunction

Tomorrow, Sunday September 8th, is an interesting astronomical event: a nice conjunction of a slim crescent moon and gibbous Venus, with Saturn hanging above and to the left of the pair.

That alone isn't anything unusual, though they'll be a lovely naked-eye sight just after nightfall. But here's the kicker: they'll be quite a bit closest during the daytime, best around 2-3 in the afternoon, Which makes for a fun exercise: can you find the crescent moon during daylight, then use it to guide you to Venus (right above it, about a degree away) and Saturn (about 10 degrees away, down and left)?

They'll be just a little east of due south, and about 40 degrees up. You'll definitely need binoculars to find Saturn, and they might help in finding the other two as well, depending on how bright and how hazy your afternoon sky is. Once you find them, a low powered telescope view should show Venus' phase and Saturn's rings. Venus is gibbous, alas; it would have been fun to see two crescents lined up one above the other.

If you have trouble finding them, wait until 3:30 pm, when they'll be transiting. At that point, you should be able to point due south, sweep your binoculars (or just your eyes) up just short of halfway to the zenith, and the moon should be there.

If you don't get a chance to watch the daylight conjunction, or don't have binoculars or a telescope handy, at least take a naked eye look at the trio at nightfall.

Mars and an early view of Comet ISON

As long as I'm reposting tips from my SJAA Ephemeris Shallow Sky column, there's another interesting thing in the sky this month: Comet C/2012 S1 ISON. Yes, that's the "super comet" that's supposed to become brighter than the moon. No, it won't be bright yet. It's still super wimpy, and worse, it's still in the morning sky, so it's not an easy or convenient target.

On the other hand, through September and October, Mars and Comet ISON will be within a few degrees of each other. So if you're willing to stay up (or get up) for early morning dark-sky observing, and you have a big telescope, this could be a nice view.

The comet won't be very impressive yet -- it's only expected to be 10th magnitude in September -- but such close proximity to Mars makes it easy to find and keep track of. In September, the pair don't rise until about 3:30am, and that won't change much for the next few months. The comet will probably stay below naked eye visibility at least for the next two months, brightening from 11th magnitude in early September to maybe 7th magnitude by Halloween.

As September opens, ISON makes a triangle with Mars and M44, the Beehive cluster. The comet stands about 2 degrees north of the Beehive and about 5 degrees east of Mars. But it closes with Mars as the month progresses: by the end of September you can find the comet about two degrees north of Mars, and by the middle of October they'll be down to only a degree apart (with ISON brightening to about ninth magnitude).

About that Beehive cluster: right now (September 7 through 9), Mars is passing right through the Beehive, like an angry red wasp among the smaller bees. Should be a nice view even if the comet isn't. It's a good binocular or even naked eye view (though great with a telescope, too). So if you find yourself up before dawn, definitely take a look.

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[ 19:34 Sep 07, 2013    More science/astro | permalink to this entry | ]

Wed, 03 Jul 2013

Mad Moon Models

[This a slight revision of my monthly "Shallow Sky" column in the SJAA Ephemeris newsletter. Looks like the Ephemeris no longer has an online HTML version, just the PDF of the whole newsletter, so I may start reposting my Ephemeris columns here more often.]

[Plate IX: The Lunar Apennines, Archemedes &c.] Last month I stumbled upon a loony moon book I hadn't seen before, one that deserves consideration by all lunar observers.

The book is The Moon: Considered as a Planet, a World, and a Satellite by James Nasmyth, C.E. and James Carpenter, F.R.A.S. It's subtitled "with twenty-six illustrative plates of lunar objects, phenomena, and scenery; numerous woodcuts &c." It was written in 1885.

Astronomers may recognize the name Nasmyth: his name is attached to a modified Cassegrain focus design used in a lot of big observatory telescopes. Astronomy was just a hobby for him, though; he was primarily a mechanical engineer. His coauthor, James Carpenter, was an astronomer at the Royal Greenwich Observatory.

The most interesting thing about their book is the plates illustrating lunar features. In 1885, photography wasn't far enough along to get good close-up photos of the moon through a telescope. But Nasmyth and Carpenter wanted to show something beyond sketches. So they built highly detailed models of some of the most interesting areas of the moon, complete with all their mountains, craters and rilles, then photographed them under the right lighting conditions for interesting shadows similar to what you'd see when that area was on the terminator.

[David North explaining the moon] I loved the idea, since I'd worked on a similar but much less ambitious project myself. Over a decade ago, before we were married, Dave North got the idea to make a 3-D model of the full moon that he could use for the SJAA astronomy class. I got drafted to help. We started by cutting a 3-foot disk of wood, on which we drew a carefully measured grid corresponding to the sections in Rukl's Atlas of the Moon. Then, section by section, we drew in the major features we wanted to incorporate. Once the drawing was done, we mixed up some spackle -- some light, and some with a little black paint in it for the mare areas -- and started building up relief on top of the features we'd sketched. The project was a lot of fun, and we use the moon model when giving talks (otherwise it hangs on the living room wall).

Nasmyth and Carpenter's models cover only small sections of the moon -- Copernicus, Plato, the Apennines -- but in amazing detail. Looking at their photos really is like looking at the moon at high magnification on a night of great seeing.

So I had to get the book. Amazon has two versions, a paperback and a hardcover. I opted for the paperback, which turns out to be scanned from a library book (there's even a scan of the pocket where the book's index card goes). Some of the scanning is good, but some of the plates come out all black. Not very satisfying.

But once I realized that an 1885 book was old enough to be public domain, I checked the web. I found two versions: one at Archive.org and one on Google Books. They're scans from two different libraries; the Archive.org scan is better, but the epub version I downloaded for my ebook reader has some garbled text and a few key plates, like Clavius, missing. The Google version is a much worse scan and I couldn't figure out if they had an epub version. I suspect the hardcover on Amazon is likely a scan from yet a fourth library.

At the risk of sounding like some crusty old Linux-head, wouldn't it be nice if these groups could cooperate on making one GOOD version rather than a bunch of bad ones?

I also discovered that the San Jose library has a copy. A REAL copy, not a scan. It gave me a nice excuse to take the glass elevator up to the 8th floor and take in the view of San Jose. And once I got it, I scanned all the moon sculpture plates myself. Sadly, like the Archive.org ebook, the San Jose copy is missing Copernicus. I wonder if vandals are cutting that page out of library copies? That makes me wince even to think of it, but I know such things happen.

Whichever version you prefer, I'd recommend that lunies get hold of a copy. It's a great introduction to planetary science, with very readable discussions of how you measure things like the distance and size of the moon. It's an even better introduction to lunar observing: if you merely go through all of their descriptions of interesting lunar areas and try to observe the features they mention, you'll have a great start on a lunar observing program that'll keep you busy for months. For experienced observers, it might give you a new appreciation of some lunar regions you thought you already knew well. Not at super-fine levels of detail -- no Alpine Valley rille -- but a lot of good discussion of each area.

[Plate XVIII: Aristarchus & Herodotus ] Other parts of the book are interesting only from a historical perspective. The physical nature of lunar features wasn't a settled issue in 1885, but Nasmyth and Carpenter feel confident that all of the major features can be explained as volcanism. Lunar craters are the calderas of enormous volcanoes; mountain ranges are volcanic too, built up from long cracks in the moon's crust, like the Cascades range in the Pacific Northwest.

There's a whole chapter on "Cracks and Radiating Streaks", including a wonderful plate of a glass ball with cracks, caused by deformation, radiating from a single point. They actually did the experiment: they filled a glass globe with water and sealed it, then "plunged it into a warm bath". The cracks that resulted really do look a bit like Tycho's rays (if you don't look TOO closely: lunar rays actually line up with the edges of the crater, not the center).

It's fun to read all the arguments that are plausible, well reasoned -- and dead wrong. The idea that craters are caused by meteorite impacts apparently hadn't even been suggested at the time.

Anyway, I enjoyed the book and would definitely recommend it. The plates and observing advice can hold their own against any modern observing book, and the rest ... is a fun historical note.

Here are some places to get it:
Amazon:

Online:

Or, try your local public library -- they might have a real copy!

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[ 16:12 Jul 03, 2013    More science/astro | permalink to this entry | ]

Wed, 08 May 2013

Gamymede whac-a-moon tonight

A couple of months ago I wrote about watching an eclipse of Europa by Jupiter's shadow. It's a game I call "Whac-a-Moon", where a moon comes out from behind Jupiter, but stays there for only a short time then disappears into eclipse. If you aren't ready for it, it's gone.

This can only happen when Jupiter's shadow is offset from Jupiter that there's a gap between the planet and the shadow as seen from Earth. Jupiter is getting low in the west, and soon we'll lose it behind the sun, but tonight, Wednesday May 8, there's a decent Ganymede Whac-a-Moon opportunity for those of us on the US west coast.

Ganymede disappears behind Jupiter at 6:45 pm PDT, still during daylight. Some time around 9:43 Ganymede reappears from behind Jupiter, but it only stays visible for a couple of minutes before entering Jupiter's eclipse. Don't trust these times I'm giving you: set up at least five minutes early, preferably more than that. And set up somewhere with a good western horizon, because Jupiter will be very low, less than 8 degrees above the horizon.

You can simulate the event on my Javascript Jupiter. When the G goes blue, that means Ganymede is in eclipse. But the simulation won't show you the interesting part: how gradual the eclipse is, as the moon slides through the edge of Jupiter's shadow. During the Europa eclipse a few months ago, I wanted to record the time of disappearance so I could adjust my code accordingly, but I found I couldn't pin it down at all -- Europa started dimming almost as soon as it emerged from behind Jupiter, and kept dimming until I couldn't convince myself I saw it any more.

So far, I've only watched Europa as it slid into eclipse by Jupiter's shadow; I haven't whacked Ganymede. But Ganymede is so much larger that I suspect the slow dimming effect will be even more obvious. Unfortunately, I'm not optimistic about being able to see it myself; we've had cloudy skies here for the last few nights, and that combined with the low western horizon may do me in. I may have to wait until autumn, when Jupiter will next be visible in our evening skies. But I hope someone reading this gets a chance to see this month's eclipse.

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[ 11:46 May 08, 2013    More science/astro | permalink to this entry | ]

Tue, 12 Mar 2013

The Europa Eclipse -- results

I wrote last week about an upcoming eclipse of Europa by Jupiter's shadow. One of the interesting things I'd found was how much the predicted times of Europa's appearance from behind Jupiter, and subsequent disappearance into Jupiter's shadow, varied depending on which program you were using. I had just recently managed to get my own Javascript Jupiter page showing eclipse events, and its times didn't agree with any of the other programs either. So I was burning with curiosity to know who was right.

The predicted times were:
Europa appears Europa disappears
XEphem 7:43 7:59
S&T Jupiter's Moons 7:40 7:44
my Javascript Jupiter 7:45 7:52
Stellarium 6:49 7:05

I was out of town on March 10. I brought along a travel scope, an Orion 80mm f/6 Orion Express. Not the perfect planetary scope, but certainly enough to see Europa. (The Galilean moons are even visible in binoculars, as long as you mount the binoculars on a tripod or otherwise hold them steady.)

I synchronized my watch and had the telescope set up by 7:35. Sure enough, there was no Europa there. But at 7:38 on the dot, I saw the first hint of Europa peeking out. No question about it. I watched, and timed, and by 7:41 the whole disk of Europa was visible and I could start to think I could see blackness between it and Jupiter. I'd been to a school star party a few days earlier and hadn't cleaned my eyepieces afterward -- oops! -- so the view was a little foggy and it was hard to tell for sure exactly when Europa's disk cleared Jupiter.

In fact, no matter which eyepiece I used, the fogginess seemed to get worse and worse. I had a hard time seeing Europa at all. Finally I realized that I was looking through a tree branch, and moved the scope. But by the time I got it moved again, Europa had gotten even harder to see. That was when I realized that it had been going into eclipse practically the whole time I was watching it. It was already significantly dimmed by 7:43, very dim indeed by 7:48 and gone -- in the 80mm -- by 7:49:20, though I suspect it still would have been visible in a larger scope with clean eyepieces.

So that's why the times in different programs varied so much! Galilean moons aren't point sources: you can't predict a single time for a moon disappearance, appearance or eclipse. Do you want to predict the beginning of the event, the end of the event or the time at the moon's center point? And that goes double for eclipses, where the moon is gradually sliding into the shadow of Jupiter's atmosphere. I found that it took over seven minutes the moon to go from full brightness to fully eclipsed. So what part of that do you predict?

All in all, a very interesting observing session. I'm looking forward to observing more of these eclipses, doing more timings, and tuning my program to give better predictions. (I notice my program was significantly late on both the appearance and the eclipse. I'll work on that. Better to err on the early side, and not miss anything!)

While I was adding eclipses to my Jupiter program, I also added longer-range predictions, so it would be easier to find out when these events will happen. Once that was implemented, I looked for upcoming Whac-a-Moon events. I found one on Mar 26, when Ganymede appears at 7:29pm PDT (add 7 hours for GMT). Europa and its shadow are transiting Jupiter's disk, too, so there's plenty to look at. Ganymede then enters eclipse at 9:40pm PDT. A long time between the events, I know, but it's easy enough to leave a scope set up in the backyard and go out to check it now and then.

These times are from my Javascript Jupiter program and may be a few minutes late. Always be ready at least five minutes early in case the predictions are off, no matter which program you use. Don't say I didn't warn you.

I found no events in April visible at night in California (for other time zones, you can generate predictions on my Javascript Jupiter page). But May 8 has a decent one: Ganymede appears at 9:44pm PDT, then disappears into eclipse at 9:46. Based on what I saw tonight with Europa, that means the moon should start to fade almost immediately after it has emerged from behind Jupiter, maybe even before it has fully emerged. Ganymede's larger size may also mean the fade-out will take longer. Stay tuned. Jupiter will be very low by then, only 7 degrees above the horizon.

Not many events to observe -- this is a bit rarer than I'd thought. Of course, there are lots of moons disappearing into eclipse and appearing from out of it every night, so watching that long gradual appearance or disappearance isn't difficult; the only rare part is when they appear briefly between Jupiter and Jupiter's shadow. That is relatively rare, and I'm glad I had a chance to catch it.

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[ 19:55 Mar 12, 2013    More science/astro | permalink to this entry | ]

Sat, 09 Mar 2013

Whac-a-Moon: Watch Europa appear and disappear this Sunday

This is an edited and updated version of my "Shallow Sky" column this month in the SJAA Ephemeris newsletter.

A few months ago, I got email from a Jupiter observer calling my attention to an interesting phenomenon of Jupiter's moons that I hadn't seen before. The person who mailed me described himself as a novice, and wasn't quite sure what he had seen, but he knew it was odd. After some further discussion we pinned it down.

He was observing Jupiter at 11/11/12 at 00.25 UT (which would have been mid-afternoon here in San Jose). Three of the moons were visible, with only Ganymede missing. Then Ganymede appeared: near Jupiter's limb, but not right on it. As he watched over the next few minutes, Ganymede seemed to be moving backward -- in toward Jupiter rather than away from it. Eventually it disappeared behind the planet.

It turned out that what he was seeing was the end of an eclipse. Jupiter was still a few months away from opposition, so the shadow thrown by the planet streamed off to one side as seen from our inner-planet vantage point on Earth. At 0:26 UT on that evening, long before he started observing, Ganymede, still far away from Jupiter's limb, had entered Jupiter's shadow and disappeared into eclipse. It took over two hours for Ganymede to cross Jupiter's shadow; but at 2:36, when it left the shadow, it hadn't yet disappeared behind the planet. So it became visible again. It wasn't until 2:50 that Ganymede finally disappeared behind Jupiter.

So it was an interesting effect -- bright Ganymede appearing out of nowhere, moving in toward Jupiter then disappearing again fourteen minutes later. It was something I'd never seen, or thought to look for. It's sort of like playing Whac-a-mole -- the moon appears only briefly, so you've got to hit it with your telescope at just the right time if you want to catch it before it disappears again.

A lot of programs don't show this eclipse effect -- including, I'm sad to say, my own Javascript Jupiter's moons web page. (I have since remedied that.) The open source program Stellarium shows the effect; on the web, Sky and Telescope's Jupiter's Moons page shows it, and even prints out a table of times of various moon events, including eclipses.

[Europa eclipse on Mar 10 2013]

These eclipse events aren't all that uncommon -- but only when the sun angle is just right. Searching in late February and early March this year, I found several events for Ganymede and Europa (though, sadly, many of them were during our daytime). By mid-March, the angles have changed so that Europa doesn't leave Jupiter's shadow until after it's disappeared behind the planet's limb; but Ganymede is farther out, so we can see Ganymede appearances all the way through March and for months after.

The most interesting view, it seems to me, is right on the boundary when the moon only appears for a short time before disappearing again. Like the Europa eclipse that's happening this Sunday night, March 10.

Reporting on that one got a little tricky -- because that's the day we switch to Daylight Savings time. I have to confess that I got a little twisted up trying to compare results between programs that use UTC and programs that use local time -- especially when the time zone converter I was using to check my math told me "That time doesn't exist!" Darnit, if we'd all just use UTC all the time, astronomy calculations would be a lot easier! (Not to mention dropping the silly Daylight Savings Time fiasco, but that's another rant.)

Before I go into the details, I want to point out that Jupiter's moons are visible even in binoculars. So even if you don't have a telescope, grab binoculars and set them up in as steady a way as you can -- if you don't have a tripod adaptor, try bracing them on the top of a gate or box.

On Sunday night, March 10, at some time around 7:40 pm PDT, Europa peeks out from behind Jupiter's northeast limb. (All times are given in PDT; add 7 hours for GMT.) The sky will still be bright here in California -- the sun sets at 7:12 that night -- but Jupiter will be 66 degrees up and well away from the sun, so it shouldn't give you too much trouble. Once Europa pops out, keep a close eye on it -- because if Sky & Tel's calculations are right, it will disappear again just four minutes later, at 7:44, into eclipse in Jupiter's shadow. It will remain invisible for almost three hours, finally reappearing out of nowhere, well off Jupiter's limb, at around 10:24 pm.

Here's a link to my Javascript Jupiter just before Europa reappears.

I want to stress that those times are approximate. In fact, I tried simulating the event in several different programs, and got wildly varying times:
Io disappears Europa appears Europa disappears Europa reappears Io appears
XEphem 7:15 7:43 7:59 10:06 10:43
S&T Jupiter's Moons 7:16 7:40 7:44 10:24 10:48
Javascript Jupiter 7:17 7:45 7:52 10:15 10:41
Stellarium 6:21 6:49 7:05 9:32 10:01

You'll note Stellarium seems to have a time zone problem ... maybe because I ran the prediction while we were still in standard time, not daylight savings time.

I'm looking forward to timing the events to see which program is most accurate. I'm betting on XEphem. Once I know the real times, maybe I can adjust my Javascript Jupiter's code to be more accurate. If anyone else times the event, please send me your times, in case something goes wrong here!

Anyway, the spread of times makes it clear that when observing this sort of phenomenon, you should always set up the telescope ten or fifteen minutes early, just in case. And ten extra minutes spent observing Jupiter -- even without moons -- is certainly never time wasted! Just keep an eye out for Europa to appear -- and be ready to whack that moon before it disappears again.

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[ 11:30 Mar 09, 2013    More science/astro | permalink to this entry | ]

Wed, 31 Oct 2012

Comparing sunset times with PyEphem

We were marveling at how early it's getting dark now -- seems like a big difference even compared to a few weeks ago. Things change fast this time of year.

Since we're bouncing back and forth a lot between southern and northern California, Dave wondered how Los Angeles days differed from San Jose days. Of course, San Jose being nearly 4 degrees farther north, it should have shorter days -- but by the weirdness of orbital mechanics that doesn't necessarily mean that the sun sets earlier in San Jose. His gut feel was that LA was actually getting an earlier sunset.

"I can calculate that," I said, and fired up a Python interpreter to check with PyEphem. Since PyEphem doesn't know San Jose (hmph! San Jose is bigger than San Francisco) I used San Francisco.

Since PyEphem's Observer class only has next_rising() and next_setting(), I had to set a start date of midnight so I could subtract the two dates properly to get the length of the day.

>>> sun = ephem.Sun()
>>> la = ephem.city('Los Angeles')
>>> sf = ephem.city('San Francisco')
>>> 
>>> mid = ephem.Date('2012/10/31 8:00')
>>> 
>>> la.next_rising(sun, start=mid)
2012/10/31 14:11:57
>>> la.next_setting(sun, start=mid)
2012/11/1 01:00:45
>>> la.next_setting(sun, start=mid) - la.next_rising(sun, start=mid)
0.45055988136300584
>>> 
>>> sf.next_rising(sun, start=mid)
2012/10/31 14:34:19
>>> sf.next_setting(sun, start=mid)
2012/11/1 01:11:44
>>> sf.next_setting(sun, start=mid) - sf.next_rising(sun, start=mid)
0.4426457611261867

So Dave's intuition was right: northern California really does have a later sunset than southern California at this time of year, even though the total day length is shorter -- the difference in sunrise time makes up for the later sunset.

How much shorter?

>>> (la.next_setting(sun, start=mid) - la.next_rising(sun, start=mid)) - (sf.next_setting(sun, start=mid) - sf.next_rising(sun, start=mid))
0.007914120236819144
>>> ((la.next_setting(sun, start=mid) - la.next_rising(sun, start=mid)) - (sf.next_setting(sun, start=mid) - sf.next_rising(sun, start=mid))) * 24
0.18993888568365946
>>> ((la.next_setting(sun, start=mid) - la.next_rising(sun, start=mid)) - (sf.next_setting(sun, start=mid) - sf.next_rising(sun, start=mid))) * 24 * 60
11.396333141019568

And we have our answer -- there's about 11 minutes difference in day length between SF and LA.

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Fri, 21 Sep 2012

Farewell, Space Shuttle Endeavour

[Space shuttle Endeavour flyby] This morning, the last space shuttle, Endeavour, made a piggyback fly-by of California cities prior to landing at LAX, where it will be trucked to its final resting place in Exposition Park. And what science and astronomy fan could resist a once in a lifetime chance to see the last shuttle in flight, piggyback on its 747 transporter?

Events kept me busy all morning, so I was late getting away. Fortunately I'd expected that and planned for it. While watching the flyby from Griffith Observatory sounded great, I suspected there would be huge crowds, no parking and there's no way I could get there in time. The Times suggested Universal City -- which I took to mean that there would be huge crowds and traffic there too. So I picked a place off the map, Blair Dr., that looked like it was easy to get to, reasonably high and located in between Griffith and Universal.

It turned out to be a good choice. There were plenty of people there, but I found a parking spot a few blocks away from where everybody was hanging out and walked back to the viewpoint where I'd seen the crowds.

[Universal Studios back lot] I looked down and the first thing I saw was a smashed jumbo jet among the wreckage of some houses. Um ... not the way I wanted to see the shuttle! But then I realized I was looking at the Universal Studios back lot. Right. Though binoculars I could even see the tram where the folks on the studio tour went right by the "plane crash". And I could look across to Universal City, where the crowds made me happy I'd decided against going there -- I bet they had some traffic jams too.

The crowd was friendly and everybody was sharing the latest rumors of the shuttle's location -- "It just flew over Santa Barbara!" "It's over West Hollywood -- get ready!" "Nope, now it's going west again, might be a while." That helped with the wait in the hot sun.

[Space shuttle Endeavour flyby] Finally, "It's coming!" And we could see it, passing south of the crowds at Universal City and coming this way ... and disappearing behind some trees. We all shifted around so we'd see it when it cleared the trees.

Only it didn't! We only got brief glimpses of it, between branches, as the shuttle flew off toward Griffith Observatory. Oh no! Were we in exactly the wrong location?

Then the word spread, from people farther down the road -- "It's turning -- get ready for another pass!" This time it came by south of us, giving us all a beautiful clear view as the 747 flew by with the shuttle and its two fighter-plane escorts.

We hung around for a few more minutes, hoping for another pass, but eventually we dispersed. The shuttle and its escorts flew on to LAX, where it will be unloaded and trucked to Exposition Park. I feel lucky to have gotten such a beautiful view of the last shuttle flight.

Photos: Space shuttle Endeavour flyover.

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[ 21:35 Sep 21, 2012    More science/astro | permalink to this entry | ]

Sun, 12 Aug 2012

A daytime Venus occultation

Tomorrow -- Monday, August 13th -- starting a little after 1 pm PDT (20 UT), the moon passes in front of Venus. That's during the day for those of us in the US, but don't worry -- both Venus and the moon are easily visible during the daytime.

The RASC handbook lists the time as exactly 1pm, but XEphem and some web sources show Venus disappearing at more like 1:30. The time isn't critical, because the most interesting part of this occultation is the lead-up, where you can see both Venus and the moon at once. The nearness of the moon will make it easy to locate Venus during the day, something that's usually a bit challenging even with this bright magnitude -4 planet.

Binoculars should show both objects just fine, though a telescope is even better. In a telescope, you'll be able to compare the phases of the two objects: the slim crescent of the moon contrasted with the half Venus.

If you've never seen a Venus occultation before, you'll be amazed at the difference between the brightness of Venus and the dimness of the moon's limb. We think of the moon as bright, but it's actually dark grey, about the same albedo (reflectivity) as asphalt; whereas Venus is covered with brightly reflective clouds.

It's a great excuse to set up a telescope or binoculars for a late lunchtime observing session and share some photons with your co-workers or anyone else who happens by. I've heard an amazing number of adults express amazement at the idea of seeing the moon during the daytime (even though they've undoubtedly seen it themselves at some point, and just don't remember it). So seeing both objects, and their phases, should be a great conversation starter outside the cafeteria or local coffeehouse.

I'd suggest setting up no later than 12:30, and earlier works fine. Even before 11, a low power eyepiece should show both the moon and Venus in the same field. Watch out for the sun! Try to find a place where you're shaded from the sun but can still see the moon. That way, not only do you stay cooler, but you're protected against accidentally swinging binoculars toward the sun and blinding yourself.

Of course, what goes behind must come out again: Venus should re-emerge from behind the dark side of the moon around 2:30 to 3 pm.

[Daytime Venus occultation] And now it's over. A fun event! It disappeared at about 1:35pm. You can see my low-tech photos here: Daytime Venus occultation, 2012-8-13.

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Wed, 06 Jun 2012

There's a big black spot on the sun today ...

[Transit of Venus, June 5 2012] After a heart-stopping day of rain on Monday, Tuesday, the day of the Venus transit astronomers have been anticipating for decades, dawned mostly clear.

For the 3 pm ingress, Dave and I set up in the backyard -- a 4.5-inch Newtonian, a Takahashi FS102, and an 80mm f/6 refractor with an eyepiece projection camera mount. I'd disliked the distraction during the annular eclipse of switching between eyepiece and camera mount, and was looking forward to having a dedicated camera scope this time.

Venus is big! There wasn't any trouble seeing it once it started its transit. I was surprised at how slowly it moved -- so much slower than a Mercury transit, though it shouldn't have been a surprise, since I knew the event would take the rest of the evening, and wouldn't be finished until well past our local sunset.

The big challenge of the day was to see the aureole -- the arc of Venus' atmosphere standing out from the sun. With the severely windy weather and turbulent air (lots of cumulus clouds) I wasn't hopeful. But as Venus reached the point where only about 1/3 of its disk remained outside the sun, the aureole became visible as a faint arc. We couldn't see it in the 4.5-inch, and it definitely isn't visible in the poorly-focused photos from the 80mm, but in the FS102 it was definitely there.

About those poorly focused pictures: I hadn't used the 80mm, an Orion Express, for photography before. It turned out its 2-inch Crayford focuser, so nice for visual use, couldn't hold the weight of a camera. With the sun high overhead, as soon as I focused, the focuser tube would start to slide downward and I couldn't lock it. I got a few shots through the 80mm, but had better luck holding a point-and-shoot camera to the eyepiece of the FS102.

Time for experiments

[Binocular projection of Venus transit] Once the excitement of ingress was over, there was time to try some experiments. I'd written about binocular projection as a way anyone, without special equipment, could watch the transit; so I wanted to make sure that worked. I held my cheap binoc (purchased for $35 many years ago at Big 5) steady on top of a tripod -- I never have gotten around to making a tripod mount for it; though if I'd wanted a more permanent setup, duct tape would have worked.

I couldn't see much projecting against the ground, and it was too windy to put a piece of paper or cardboard down, but an old whiteboard made a perfect solar projection screen. There was n trouble at all seeing Venus and some of the larger sunspots projected onto the whiteboard.

As the transit went on, we settled down to a routine of popping outside the office every now and then to check on the transit. Very civilized. But the transit lasted until past sunset, and our western horizon is blocked by buildings. I wanted some sunset shots. So we took a break for dinner, then drove up into the hills to look for a place with a good ocean view.

The sunset expedition

Our first idea, a pullout off Highway 9, had looked promising in Google Earth but turned out to have trees and a hill (that somehow hadn't shown up in Google Earth) blocking the sunset. So back up highway 9 and over to Russian Ridge, where I remembered a trail entrance on the western side of the ridge that might serve. Sure enough, it gave us a great sunset view. There was only parking space for one car, but fortunately that's all we needed. And we weren't the only transit watchers there -- someone else had hiked in from the main parking lot carrying a solar filter, so we joined him on the hillside as we waited for sunset.

[Mak 90 with solar filter] I'd brought the 80mm refractor for visual observing and the 90 Mak for camerawork. I didn't have a filter for the Mak, but Dave had some Baader solar film, so earlier in the afternoon I'd whipped up a filter. A Baskin-Robbins ice cream container lid turned out to be the perfect size. Well, almost perfect -- it was just a trifle too large, but some pads cut from an old mouse pad and taped inside the lid made it fit perfectly. Dave used the Baader film, some foam and masking tape to make a couple of filters for his binocular.

The sun sank through a series of marine cloud layers. Through the scopes it looked more like Jupiter than the sun, with Jupiter's banding -- and Venus' silhouette even looked like the shadow of one of Jupiter's moons.

[off-axis aperture stops from ice cream containers] Finally the sun got so low, and so obscured by clouds, that it seemed safe to take the solar filter off the 90mm camera rig. (Of course, we kept the solar filters on the other scope and binocular for visual observing.) But even at the camera's fastest shutter speed, 1/4000, the sun came out vastly overexposed with 90mm of aperture feeding it at f/5.6.

I had suspected that might be a problem, so I'd prepared a couple of off-axis stops for the Mak, to cover most of the aperture leaving only a small hole open. Again, BR ice cream containers turned out to be perfect. I painted the insides flat black to eliminate reflections, then cut holes in the ends -- one about the size of a quarter, the other quite a bit larger. It turned out I didn't use the larger stop at all, and it would have been handy to have one smaller than the quarter-sized one -- even with that stop, the sun was overexposed at first even at 1/4000 and I had to go back to the solar filter for a while.

[Venus transit at sunset] [Venus transit at sunset] I was happy with the results, though -- I got a nice series of sunset photos complete with Venus silhouette.

More clouds rolled in as we packed up, providing a gorgeous blue-and-pink sunset sky backdrop for our short walk back to the car. What a lovely day for such a rare celestial event!

Photos here: Venus Transit, June 5 2012.

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Fri, 01 Jun 2012

Observe the 2012 Venus transit!

[Venus transit 2004 from Chicago. Copyright © 2004 by Bill Arnett] June 5 brings the last Venus transit until 2117, when Venus will pass across the face of the sun -- the second of the only two Venus transits any of us will see in our lives. (The first, pictured in this lovely image from Bill Arnett, was in 2004, visible on the east coast of the US but not visible here in California.)

Venus is just a small spot against the vastness of the sun -- the skies won't dim like in an eclipse, and you need equipment to see it. So why should a non-astronomer care?

Mostly because it's so rare. Venus transits happen in pairs with more than a century between successive pairs: the last transit before 2004 was in 1882, and the next one after this week's won't happen until 2117. The entire 20th century passed without a single Venus transit.

They're historically interesting, too. It was in 1663 that Scottish mathematician James Gregory proposed that you could calculate the distance to the Sun by measuring a Venus transit, by observing at many different places on earth and measuring parallax. Edmund Halley (of Halley's Comet fame) tried this method during the Mercury transit of 1676, but since Mercury is so much closer to the sun and farther from us, the results weren't good enough. Unfortunately, Halley died in 1742, too early for the Venus transit of 1761.

But lots of other astronomers were ready, mounting expeditions that year to Siberia, Norway, Newfoundland and Madagascar (some of these expeditions were major adventures, and several books have been written about them). They followed up in 1769 with expeditions to Hudson Bay, Baja California, Norway, St Petersburg, Philadelphia... and the first voyage of Captain Cook to Tahiti, where they observed the transit at a location that's still called "Point Venus" today.

[Black drop effect] Alas, their measurements weren't as accurate as they had hoped. The exact times of a Venus transit turn out to be difficult to measure due to the dreaded black drop effect, where the black circle of Venus can seem to elongate into a teardrop shape as it "tears away" from the edge of the sun. The effect seems to be caused by blurring from our own atmosphere (poor seeing) combined with telescope diffraction. So the steadier your seeing is, and the bigger and better your optics, the less likely you are to see the black drop.

How to see the transit

First, if you don't have a telescope of your own, don't despair -- head to your local astronomy club. Here in the bay area there are dozens of clubs, and just about all of them have public star parties planned for the Venus transit. There are events planned at local science museums, planetaria and schools as well. A few bay area links: San Jose Astronomical Association, Peninsula Astronomical Society, San Francisco Sidewalk Astronomers, San Francisco Amateur Astronomers, or any of the others on the AANC's list of Amateur Astronomy Clubs in Northern California or the SF Chronicle's list of astronomy clubs. And the Hubble Space Telescope will be watching the transit by looking at light reflected off the moon.

But suppose you're viewing it on your own?

Of course, this being a solar event, you can't look at it directly -- you need a filter or other apparatus. No need for a fancy H-alpha filter -- a white light solar filter is fine, the kind that covers the aperture of the telescope. (Don't use the kind that screw into the eyepiece! They can overheat and crack while you're looking through them.)

You don't need a big telescope. I used an Orion solar filter on my little 80mm f/7 refractor for the last Mercury transit and it worked great. And Venus is much larger than Mercury, at about 50 arcseconds versus Mercury's 12 (the sun is half a degree, or 30 arcminutes). So if you've seen a Mercury transit, you can imagine how much easier and more spectacular a Venus transit can be.

If you use binoculars, either make sure that you have solar filters for both sides, or keep one side covered at all times. If your telescope has a finderscope, keep it covered.

If you can't find a solar filter in time for the transit, you can set up your telescope to project the sun's image onto a white board or sheet of paper. (This is how Jeremiah Horrocks made the first known Venus transit observation.)

Use a cheap, low powered eyepiece for this: the eyepiece will get hot, and you don't want to risk damaging a fancy eyepiece. Be careful with solar projection -- make sure nobody nearby can walk between the telescope and the surface you're using as a projection screen, or place their hands or eyes in the light path. A web search for solar projection will uncover other tips.

You can project the sun's image with binoculars, too, so don't feel left out if you don't have a telescope. You'll definitely want a tripod mount. I tried binocular projection during last month's annular eclipse, and found it very fiddly to hold the binoculars just right. Don't count on being able to hold them steady while also looking for Venus on the projected image. If you don't have a tripod adapter (try Orion), cobble something together with duct tape and a block of wood, or whatever you have handy.

And do try to get a good white surface to project onto. Concrete worked well enough for the solar eclipse, but you'll want better resolution for Venus.

Timeline

When does this all happen?

Seen from the bay area, Venus begins its ingress onto the disc of the sun on 3:06 PDT on the afternoon of June 5. The transit continues until after the sun sets at 8:26. So we won't get to see egress. Venus's exit from the face of the sun, but it's the mirror image of what we'll see at ingress.

Ingress has two parts: first contact, when the edge of Venus's disk first touches the outside of the sun's disk, and "internal ingress" or second contact, when Venus's disk is fully inside that of the sun. Second contact is the most interesting period of the transit, since it's when the "black drop effect" occurs.

[Venus transit aureole by Lorenzo Comolli [Gruppo Astronomico Tradatese] and the VT-2004 programme] And if you have a good telescope and filter and you're blessed with especially good seeing around the time of second contact, try looking for the aureole, an arc of light just outside of the solar disk made by the refraction of sunlight through Venus's atmosphere. Amazingly, the aureole has the same surface brightness as the sun's surface, and is said to be possible to see even through a solar filter. That's something you'll never see in a Mercury transit! (Follow the link on the image to see Lorenzo Comolli's amazing aureole photo in more detail, along with other great aureole images courtesy of the VT-2004 programme.)

Here's the time table for the bay area (from the table on NASA's eclipse website):
First contact: 3:06:20
Internal ingress: 3:23:56
Maximum transit: 6:25:30
Sunset: 8:26

At first contact, the sun will still be high for bay area observers, 60° up. By maximum transit the pair will have sunk to 21°, still plenty high enough to see the spectacle. Photographers will want to wait around for sunset for a chance at some spectacular photos, like the Bill Arnett photo at the top of this article, taken from Chicago.

Want more details or times from other locations? transitofvenus.org has plenty of links, as does Everything you need to know about next week’s Transit of Venus.

Stay safe, and enjoy this once-in-a-lifetime event!

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[ 13:04 Jun 01, 2012    More science/astro | permalink to this entry | ]

Tue, 22 May 2012

Saw the "Ring of Fire" 2012 annular eclipse

[Annular eclipse 2012] I've just seen the annular eclipse, and what a lovely sight it was!

This was only my second significant solar eclipse, the first being a partial when I was a teenager. So I was pretty excited about an annular so nearby -- the centerline was only about a 4-hour drive from home.

We'd made arrangements to join the Shasta astronomy club's eclipse party at Whiskeytown Lake, up in the Trinity Alps. Sounded like a lovely spot, and we'd be able to trade views with the members of the local astronomy club as well as showing off the eclipse to the public. As astronomers bringing telescopes, we'd get reserved parking and didn't even have to pay the park fee. Sounded good!

Not knowing whether we might hit traffic, we left home first thing in the morning, hours earlier than we figured was really necessary. A good thing, as it turned out. Not because we hit any traffic -- but because when we got to the site, it was a zoo. There were cars idling everywhere, milling up and down every road looking for parking spots. We waited in the queue at the formal site, and finally got to the front of the line, where we told the ranger we were bringing telescopes for the event. He said well, um, we could drive in and unload, but there was no parking so we'd just have to drive out after unloading, hope to find a parking spot on the road somewhere, and walk back.

What a fiasco!

After taking a long look at the constant stream of cars inching along in both directions and the chaotic crowd at the site, we decided the better part of valor was to leave this vale of tears and high-tail it back to our motel in Red Bluff, only little farther south of the centerline and still well within the path of annularity. Fortunately we'd left plenty of extra time, so we made it back with time to spare.

The Annular Eclipse itself

[early stage of annular eclipse 2012, showing sunspots] One striking thing about watching the eclipse through a telescope was how fast the moon moves. The sun was well decorated with several excellent large sunspot groups, so we were able to watch the moon swallow them bit by bit.

Some of the darker sunspot umbras even showed something like a black drop effect as they disappeared behind the moon. We couldn't see the same effect on the smaller sunspot groups, or on the penumbras. [black drop at end of annularity] There was also a pronounced black drop effect at the onset and end of annularity.

The seeing was surprisingly good, as solar observing goes. Not only could we see good detail on the sunspot groups and solar faculae, but we could easily see irregularities in the shape of the moon's surface -- in particular one small sharp mountain peak on the leading edge, and what looked like a raised crater wall farther south on that leading edge. We never did get a satisfactory identification on either feature.

[pinhole eclipse viewing] After writing and speaking about eclipse viewing, I felt honor bound to try viewing with pinholes of several sizes. I found that during early stages of the eclipse, the pinholes had to be both small (under about 5 mm) and fairly round to show much. Later in the eclipse, nearly anything worked to show the crescent or the annular ring, including interlaced fingers or the shadow of a pine tree on the wall. I wish I'd remembered to take an actual hole punch, which would have been just about perfect.

[binocular projection for eclipse] I also tried projection through binoculars, and convinced myself that it would probably work as a means of viewing next month's Venus transit -- but only with the binoculars on a tripod. Hand-holding them is fiddly and difficult. (Of course, never look through binoculars at the sun without a solar filter.) Look for an upcoming article with more details on binocular projection.

The cast of characters

For us, the motel parking lot worked out great. We were staying at the Crystal Motel in Red Bluff, an unassuming little motel that proved to be clean and quiet, with friendly, helpful staff and the fastest motel wi-fi connection I've ever seen. Maybe not the most scenic of locations, but that was balanced by the convenience of having the car and room so close by.

And we were able to show the eclipse to locals and motel guests who wouldn't have been able to see it otherwise. Many of these people, living right in the eclipse path, didn't even know there was an eclipse happening, so poor had the media coverage been. (That was true in the bay area too -- most people I talked to last week didn't know there was an eclipse coming up, let alone how or where to view it.)

We showed the eclipse to quite a cast of characters --

In between visitors, we had plenty of time to fiddle with equipment, take photos, and take breaks sitting in the shade to cool down. (Annularity was pleasantly cool, but the rest of the eclipse stayed hot on an over 90 degree central valley day.)

There's a lot to be said for sidewalk astronomy! Overall, I'm glad we ended up where we did rather than in that Whiskeytown chaos.

Here's my collection of Images from the "Ring of Fire" Annular Eclipse, May 2012, from Red Bluff, CA.

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[ 11:42 May 22, 2012    More science/astro | permalink to this entry | ]

Wed, 16 May 2012

Ring of Fire: 2012 annular eclipse

[Solar annular eclipse of January 15, 2010 in Jinan, Republic of China, by A013231 on Wikimedia Commons.] This Sunday, May 20th, the western half of the US will be treated to an annular solar eclipse.

Annular means that the moon is a bit farther away than usual, so it won't completely cover the sun even if you travel to the eclipse centerline. Why? Well, the moon's orbit around the earth isn't perfectly circular, so sometimes it's farther away, sometimes nearer. Remember all the hype two weeks ago about the "supermoon", where it was unusually close at full moon? The other side of that is that during this eclipse, at new moon, the moon is unusually far away, and therefore a little smaller, not quite big enough to cover the sun.

Since the sun will never be totally covered, make sure you have a safe solar filter for this one -- don't look with your naked eyes! You want a solar filter anyway, if you have any kind of telescope or even binoculars, because of next month's once-in-a-lifetime Venus transit (I'll write about that separately). But if you don't have a solar filter and absolutely can't get one in time, read on -- I'll have some suggestions later even for people without any sort of optical aid.

But first, the path of the eclipse. Here in the bay area, we're just a bit south of the southern limit of the annular path, which passes just south of the town of Redway, through Covelo, just south of Willows, then just misses Yuba City and Auburn. If you want to be closer to the centerline, go camping at Lassen National Park or Lake Shasta, or head to Reno or Tahoe If you're inclined to travel, NASA has a great interactive 2012 eclipse map you can use to check out possible locations.

Even back in the bay area, we still get a darn good dinner show. The partial eclipse starts at 5:17 pm PDT, with maximum eclipse at 6:33. The sun will be 18 degrees above the horizon at that point, and 89% eclipsed. Compare that with 97% for a site right on the centerline -- remember, since this is an annular eclipse, no place sees 100% coverage. The partial eclipse ends at 7:40 -- still well before sunset, which isn't until 8:11.

Photographers, if you want a shot of an annular eclipse as the sun sets, you'll need to head east, to Albuquerque, NM or Lubbock, TX. A little before sunset, the centerline also crosses near a lot of great vacation spots like Bryce, Zion and Canyon de Chelly.

[eclipse viewed through leaves] I mentioned that even without a solar filter, there are ways of watching the eclipse. The simplest is with a pinhole. You don't need to use an actual pin -- the size and shape of the hole isn't critical, as you can see in this image of the sun through the leaves of a tree during a 2005 eclipse in Malta. If you don't have a leafy tree handy, you can even lace your fingers together and look at the shadow of your hands. This eclipse will be very low in the sky, continuing through sunset, so you may need to project its shadow onto a wall rather than the ground.

If you have some time to prepare, take a piece of cardboard and punch a few holes through it. Try different sizes -- an actual pinhole, a BBQ skewer, a 3-hole punch, maybe even bigger holes up to the size of a penny. You might also try using aluminum foil -- you can get very clean circular holes that way, which might give a crisper image. Here's a good page on eclipse pinhole projection. What works best? I don't remember! It's been a very long time since the last eclipse here! Do the experiment! I know I will be.

[Solar projection with a Dobsonian] If you do have a telescope or binoculars but couldn't get a solar filter in time, don't despair. Instead of looking through the eyepiece, you can project the sun's image onto a white screen or even the ground or a wall. Use a cheap, low-power eyepiece -- any eyepiece you use for solar projection will get very hot, and you don't want to risk ruining a fancy one.

Point the telescope at the sun -- it's easy to tell when it's lined up by watching the shadow of the telescope -- and rotate the eyepiece so that it's aimed at your screen, which can be as simple as a sheet of paper. Be careful where that eyepiece is aimed -- make sure no one can walk through the path or put their hand in the way, and if you have a finderscope, make sure it's covered. This solar projection method works with binoculars too, but you'll want to mount them on a tripod so you don't have to hold them the whole time.

Of course, another great way to watch the eclipse is with your local astronomy club. I expect every club in the bay area -- and there are a lot of them -- will have telescopes out to share the eclipse with the public. So check with your local club -- San Jose Astronomical Association, Peninsula Astronomical Society, San Francisco Sidewalk Astronomers, San Francisco Amateur Astronomers, or any of the others on the AANC's list of Amateur Astronomy Clubs in Northern California or the SF Chronicle's list of astronomy clubs.

This eclipse should be pretty cool -- and a great chance to test out your solar equipment before next month's Venus transit.

When I went to put the event on my wall calendar last month, I discovered the calendar already had an entry for May 20: it's the start of Bear Awareness Week. So if you head up to Lassen or Shasta to watch the eclipse, be sure to be aware of the bears! (Also, maybe I should get a calendar that's a little more in tune with the sky.)

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[ 21:12 May 16, 2012    More science/astro | permalink to this entry | ]

Fri, 27 Apr 2012

Venus is at its brightest -- why? And how to calculate it

Venus has been a beautiful sight in the evening sky for months, but at the end of April it's reaching a brightness peak, magnitude -4.7.

By then, if you look at it in a telescope or even good binoculars, you'll see it has waned to a crescent. That's a bit non-obvious: when the moon is a crescent, it's a lot fainter than a full moon. So why is Venus brightest in its crescent phase?

It has to do with their orbits. The moon is always about the same distance away, about 385,000 km or 239,000 miles (I've owned cars with more miles than that!), though it varies a little, from 362,600 km at perigee to 405,400 km at apogee.

When we look at the full moon, not only are we seeing the whole Earth-facing surface illuminated, but the central part of that light is reflecting straight up off the moon's surface. When we look at a crescent moon, we're seeing light that's near the moon's sunrise or sunset point -- dimmer and more spread out than the concentrated light of noon -- and in addition we're seeing less of it.

Venus, in contrast, varies its distance from us immensely. We can't see Venus when it's "full", because it's on the other side of the sun from us and lost in the sun's glow. It'll next be there a year from now, in April of 2013. But if we could see it when it's full, Venus would be a distant 1.7 AU from us. An AU is an Astronomical Unit, the average distance of the earth from the sun or about 89 million miles, so Venus when it's full is about 170 million miles away. Its disk is a tiny 9.9 arcseconds (an arcsecond is 1/3600 of a degree) -- about the size of Mars this month.

In contrast, when we look at the crescent Venus around the end of this month, although we're only seeing about 28% of its surface illuminated, and that only with glancing twilight rays, it's much closer to us -- less than half an AU, or about 45 million miles -- and its disk extends a huge 37 arcseconds, bigger than Jupiter this month.

Of course, eventually, as Venus pulls between us and the sun, its crescent gets so slim that even its huge size can't compensate. So its peak brightness happens when those two curves cross, when the disk is somewhere around 27% illuminated, as happens at the end of this month and the beginning of May.

Exactly when? Good question. The RASC Handbook says Venus' "greatest illuminated extent" is on April 30, but PyEphem and XEphem say Venus is actually brighter from May 3-8 ... and when it emerges from the sun's glare and moves into the morning sky in June, it'll be slightly brighter still, peaking at magnitude -4.8 in the first week of July.)

Tracking Venus with PyEphem

When I started my Shallow Sky column this month, I saw the notice of Venus's maximum brightness and greatest illuminated extent in the RASC Handbook. But I wanted more details -- how much did its distance and size really change, when would the brightness peak again as it emerged from the sun's glare, when would it next be "full"?

PyEphem made it easy to calculate all this. Just create an ephem.Venus() object, calculate its values for any date of interest, then print out parameters like phase, mag, earth_distance and size. In just a few minutes of programming, I had a nice table of Venus data.

import ephem

venus = ephem.Venus()

print '%10s   %6s %6s %6s %6s' % ('date', '%', 'mag', 'dist', 'size')
def print_venus(when) :
    venus.compute(when)
    fmt = '%02d-%02d-%02d   %6.2f %6.2f %6.2f %6.2f'
    trip = when.triple()
    print fmt % (trip[0], trip[1], trip[2],
                 venus.phase, venus.mag, venus.earth_distance, venus.size)

# Loop from the beginning of 2012 through the middle of 2013:
d = ephem.date('2012')
end_date = ephem.date('2013/6/1')
while d < end_date :
    print_venus(d)
    # Add a week:
    d = ephem.date(d + ephem.hour * 24)

I've found PyEphem very handy for calculations like this -- and it's great to be able to double-check listings in other publications.

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[ 14:44 Apr 27, 2012    More science/astro | permalink to this entry | ]

Thu, 29 Dec 2011

Plotting the Analemma

My SJAA planet-observing column for January is about the Analemma and the Equation of Time.

The analemma is that funny figure-eight you see on world globes in the middle of the Pacific Ocean. Its shape is the shape traced out by the sun in the sky, if you mark its position at precisely the same time of day over the course of an entire year.

The analemma has two components: the vertical component represents the sun's declination, how far north or south it is in our sky. The horizontal component represents the equation of time.

The equation of time describes how the sun moves relatively faster or slower at different times of year. It, too, has two components: it's the sum of two sine waves, one representing how the earth speeds up and slows down as it moves in its elliptical orbit, the other a function the tilt (or "obliquity") of the earth's axis compared to its orbital plane, the ecliptic.

[components of the Equation of time] The Wikipedia page for Equation of time includes a link to a lovely piece of R code by Thomas Steiner showing how the two components relate. It's labeled in German, but since the source is included, I was able to add English labels and use it for my article.

But if you look at photos of real analemmas in the sky, they're always tilted. Shouldn't they be vertical? Why are they tilted, and how does the tilt vary with location? To find out, I wanted a program to calculate the analemma.

Calculating analemmas in PyEphem

The very useful astronomy Python package PyEphem makes it easy to calculate the position of any astronomical object for a specific location. Install it with: easy_install pyephem for Python 2, or easy_install ephem for Python 3.

import ephem
observer = ephem.city('San Francisco')
sun = ephem.Sun()
sun.compute(observer)
print sun.alt, sun.az

The alt and az are the altitude and azimuth of the sun right now. They're printed as strings: 25:23:16.6 203:49:35.6 but they're actually type 'ephem.Angle', so float(sun.alt) will give you a number in radians that you can use for calculations.

Of course, you can specify any location, not just major cities. PyEphem doesn't know San Jose, so here's the approximate location of Houge Park where the San Jose Astronomical Association meets:

observer = ephem.Observer()
observer.name = "San Jose"
observer.lon = '-121:56.8'
observer.lat = '37:15.55'

You can also specify elevation, barometric pressure and other parameters.

So here's a simple analemma, calculating the sun's position at noon on the 15th of each month of 2011:

    for m in range(1, 13) :
        observer.date('2011/%d/15 12:00' % (m))
        sun.compute(observer)

I used a simple PyGTK window to plot sun.az and sun.alt, so once it was initialized, I drew the points like this:

    # Y scale is 45 degrees (PI/2), horizon to halfway to zenith:
    y = int(self.height - float(self.sun.alt) * self.height / math.pi)
    # So make X scale 45 degrees too, centered around due south.
    # Want az = PI to come out at x = width/2.
    x = int(float(self.sun.az) * self.width / math.pi / 2)
    # print self.sun.az, float(self.sun.az), float(self.sun.alt), x, y
    self.drawing_area.window.draw_arc(self.xgc, True, x, y, 4, 4, 0, 23040)

So now you just need to calculate the sun's position at the same time of day but different dates spread throughout the year.

[analemma in San Jose at noon clock time] And my 12-noon analemma came out almost vertical! Maybe the tilt I saw in analemma photos was just a function of taking the photo early in the morning or late in the afternoon? To find out, I calculated the analemma for 7:30am and 4:30pm, and sure enough, those were tilted.

But wait -- notice my noon analemma was almost vertical -- but it wasn't exactly vertical. Why was it skewed at all?

Time is always a problem

As always with astronomy programs, time zones turned out to be the hardest part of the project. I tried to add other locations to my program and immediately ran into a problem.

The ephem.Date class always uses UTC, and has no concept of converting to the observer's timezone. You can convert to the timezone of the person running the program with localtime, but that's not useful when you're trying to plot an analemma at local noon.

At first, I was only calculating analemmas for my own location. So I set time to '20:00', that being the UTC for my local noon. And I got the image at right. It's an analemma, all right, and it's almost vertical. Almost ... but not quite. What was up?

Well, I was calculating for 12 noon clock time -- but clock time isn't the same as mean solar time unless you're right in the middle of your time zone.

You can calculate what your real localtime is (regardless of what politicians say your time zone should be) by using your longitude rather than your official time zone:

    date = '2011/%d/12 12:00' % (m)
    adjtime = ephem.date(ephem.date(date) \
                    - float(self.observer.lon) * 12 / math.pi * ephem.hour)
    observer.date = adjtime

Maybe that needs a little explaining. I take the initial time string, like '2011/12/15 12:00', and convert it to an ephem.date. The number of hours I want to adjust is my longitude (in radians) times 12 divided by pi -- that's because if you go pi (180) degrees to the other side of the earth, you'll be 12 hours off. Finally, I have to multiply that by ephem.hour because ... um, because that's the way to add hours in PyEphem and they don't really document the internals of ephem.Date.

[analemma in San Jose at noon clock time] Set the observer date to this adjusted time before calculating your analemma, and you get the much more vertical figure you see here. This also explains why the morning and evening analemmas weren't symmetrical in the previous run.

This code is location independent, so now I can run my analemma program on a city name, or specify longitude and latitude.

PyEphem turned out to be a great tool for exploring analemmas. But to really understand analemma shapes, I had more exploring to do. I'll write about that, and post my complete analemma program, in the next article.

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[ 20:54 Dec 29, 2011    More science/astro | permalink to this entry | ]

Thu, 22 Dec 2011

Calculating the Solstice and shortest day

Today is the winter solstice -- the official beginning of winter.

The solstice is determined by the Earth's tilt on its axis, not anything to do with the shape of its orbit: the solstice is the point when the poles come closest to pointing toward or away from the sun. To us, standing on Earth, that means the winter solstice is the day when the sun's highest point in the sky is lowest.

You can calculate the exact time of the equinox using the handy Python package PyEphem. Install it with: easy_install pyephem for Python 2, or easy_install ephem for Python 3. Then ask it for the date of the next or previous equinox. You have to give it a starting date, so I'll pick a date in late summer that's nowhere near the solstice:

>>> ephem.next_solstice('2011/8/1')
2011/12/22 05:29:52
That agrees with my RASC Observer's Handbook: Dec 22, 5:30 UTC. (Whew!)

PyEphem gives all times in UTC, so, since I'm in California, I subtract 8 hours to find out that the solstice was actually last night at 9:30. If I'm lazy, I can get PyEphem to do the subtraction for me:

ephem.date(ephem.next_solstice('2011/8/1') - 8./24)
2011/12/21 21:29:52
I used 8./24 because PyEphem's dates are in decimal days, so in order to subtract 8 hours I have to convert that into a fraction of a 24-hour day. The decimal point after the 8 is to get Python to do the division in floating point, otherwise it'll do an integer division and subtract int(8/24) = 0.

The shortest day

The winter solstice also pretty much marks the shortest day of the year. But was the shortest day yesterday, or today? To check that, set up an "observer" at a specific place on Earth, since sunrise and sunset times vary depending on where you are. PyEphem doesn't know about San Jose, so I'll use San Francisco:

>>> import ephem
>>> observer = ephem.city("San Francisco")
>>> sun = ephem.Sun()
>>> for i in range(20,25) :
...   d = '2011/12/%i 20:00' % i
...   print d, (observer.next_setting(sun, d) - observer.previous_rising(sun, d)) * 24
2011/12/20 20:00 9.56007901422
2011/12/21 20:00 9.55920379754
2011/12/22 20:00 9.55932991847
2011/12/23 20:00 9.56045709446
2011/12/24 20:00 9.56258416496
I'm multiplying by 24 to get hours rather than decimal days.

So the shortest day, at least here in the bay area, was actually yesterday, 2011/12/21. Not too surprising, since the solstice wasn't that long after sunset yesterday.

If you look at the actual sunrise and sunset times, you'll find that the latest sunrise and earliest sunset don't correspond to the solstice or the shortest day. But that's all tied up with the equation of time and the analemma ... and I'll cover that in a separate article.

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[ 11:28 Dec 22, 2011    More science/astro | permalink to this entry | ]

Tue, 07 Jun 2011

Make your own Saturn sketching template with GIMP

My SJAA Ephemeris planetary astronomy column for next month will discuss Saturn, among other topics, since Saturn is the main planet visible in the evening sky right now.

Saturn has some storms visible right now in the north polar and equatorial bands, and a great way to focus your attention to see more detail through a telescope, especially on subtle details like Saturnian storms, is to take pencil and paper and sketch what you see. I've recommended sketching in my column many times before, but don't talk about it on the blog very often.

When sketching Saturn, it helps to start with a template, so you can concentrate on the interesting details of the rings and bands rather than fussing over trying to get the exact width of the rings right. Saturn's tilt changes with time -- right now it's tilted at 8° to observers here on Earth -- so sometimes the rings are open wide, sometimes they're narrow, and sometimes (as last year) they're edge-on and invisible to us. That's a hassle to try to get right in a sketch, when you'd rather be focusing on the gaps in the rings and the pastel colors of the cloud bands on the planet.

ALPO, the Association of Lunar and Planetary Observers, makes templates for sketching Saturn; but I had trouble finding any online that showed a tilt appropriate for this month's Saturn. You can get observing materials by joining ALPO, but sheesh! you shouldn't have to join an organization just to get a simple sketching template. And I wanted one for my column. Besides, the ALPO templates fill in too much detail -- they don't really give you a chance to do your own ring sketch.

So here's an easy way to make a Saturn sketching template with GIMP.

[Saturn sketch template]

Start with an image

You can calculate the aspect ratio you need for the planet from the ring tilt, but why go to all that trouble? I started with an image of Saturn I got by running XEphem. Call up View->Saturn, then make the window as big as you can. Of course, you may substitute any planetarium program of your choosing, as long as it shows Saturn with the right ring tilt.

I used GIMP's screenshot facility to open this as an image: File->Create->Screenshot..., then Select a region to grab.

You can also use a recent photo of Saturn. The point here is to get something that's the right shape: it doesn't matter if it's beautiful or large.

Fix the rotation and size

You want the rings horizontal, if they're not already. Use GIMP's Free Rotate tool to do that. You can eyeball it to make it approximately right, or if you want to be more accurate, use the Measure tool (the icon looks like a drawing compass) to measure from one edge of the rings to the other and note the angle in the status bar at the bottom of the window. Then when you use Free Rotate, type in the number you measured.

You'll be printing this out on sketching paper, so if the original image is small, use Image->Scale to expand it. Remember, you won't be looking at this original image -- it's just for tracing -- so don't worry if the image comes out fuzzy after you scale it up. I made mine about 1000 pixels wide.

Make a white background layer

Layer->New Layer... to make a new layer; check "white" in the dialog. Then click the eyeball icon next to it in the Layers dialog to make it invisible. You'll want it later.

Outline the planet on its own layer

Layer->New Layer... to make a new layer; this time make it transparent, not white. I named mine "planet", since this is where I'll draw the ellipse for the planet. (Yes, Saturn is an ellipse, not a sphere. So is the Earth, for that matter, but Saturn is a lot less spherical than Earth is.)

Choose the ellipse selection tool and drag out a selection that matches the outer edges of the planet. Use the resize handles to adjust the selection until it fits as closely as you can manage.

In the Toolbox or the Brushes dialog, choose the smallest hard brush, "Circle (01)".

Then Edit->Stroke Selection.... Click "Stroke with a paint tool", and click Stroke.

Tip: You may notice my template ended up with very jaggy lines. That's a common artifact of GIMP's Stroke Selection. I'm not worried about it for a sketching template, but if the jaggies bother you, you can get a much smoother line by converting the selection to a path and stroking the path instead of the selection.

Preview your work so far

Go back to the Layers dialog and make that white layer visible again, so you can see the outline you just made. You may want to do Select->None and click on some tool other than ellipse select, so the selection outline disappears and you can see the line better.

If you're not happy with your planet outline, Edit->Undo and repeat with a different selection, a thicker line or whatever.

Outline the rings on their own layer

Repeat what you just did for the planet, this time for the rings. I recommend using a new layer for just the rings (you'll see why in the next step).

I outlined just the outside of the rings, so the sketch can show the ring thickness. ALPO's templates don't do this, but how much ring you can see can vary based on seeing conditions. If you want the inner edge of the ring on your template, add it now.

Erase the hidden parts of the ring and planet outlines

You can't see the rings where they go behind the planet, or the part of the planet hidden by the rings. And you don't want your template lines spoiling your sketch in those regions. So use GIMP's eraser tool and a large brush to erase the appropriate parts.

This is a little easier if you used separate layers for the rings and planet: you won't have to be as careful with the eraser. But it's not a big deal: this is a template, not a finished artwork, and you're going to be drawing over it anyway. So don't sweat it too much.

Optionally, make the lines fainter

I made the template lines fainter using the Opacity slider in the Layers dialog on the planet and ring layers. Of course, you can just draw in grey in the first place, but I like being able to decide afterward what color I want, or change it later.

Label the template

Trust me, you'll be really annoyed if you decide in 2026 that you want to make another Saturn sketch, find your old template but can't remember what ring tilt it's for. So use the Text tool to label either the current date or the approximate ring tilt. Or put that information in an image comment under Image->Image Properties..., or in the filename.

Save your template as XCF.gz, save a copy in some other format like jpg, png or gif, and you're ready to print templates on paper. Then go out and sketch Saturn!

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[ 15:13 Jun 07, 2011    More science/astro | permalink to this entry | ]

Sun, 13 Mar 2011

Measuring Mars Methane -- Messy!

I write a monthly column for the San Jose Astronomical Association. Usually I don't reprint the columns here, but last month's column, Worlds of Controversy, discussed several recently controversial topics in planetary science.

One of the topics was the issue of methane on Mars -- or lack thereof. We've all read the articles about how the measurements of Mars methane points to possible signs of life, woohoo! But none of the articles cover the problems with those measurements, as described in a recent paper by Kevin Zahnle, Richard S. Freedmana and David C. Catling: Is there methane on Mars?

Lack of life on Mars isn't sexy, I guess; The Economist was the only mainstream publication covering Kevin's paper, in an excellent article, Methane on Mars: Now you don't...

Here's the short summary from my column last month:

I'm sure you've seen articles on Martian methane. Methane doesn't last long in the atmosphere -- only a few hundred years -- so if it's there, it's being replenished somehow. On Earth, one of the most common ways to produce methane is through biological processes. Life on Mars! Whoopee! So everyone wants to see methane on Mars, and it makes for great headlines.

The problem, according to Kevin, is that the Mars measurements show changes on a scale much shorter than hundreds of years: they fluctuate on a seasonal basis. That's tough to explain. Known atmospheric oxidation processes wouldn't get rid of methane fast enough, so you'd need to invent some even more exotic process -- perhaps methane-eating bacteria in the Martian soil? -- to account for the drops.

Worse, the measurements showing methane aren't very reliable. The evidence is spectroscopic: methane absorbs light at several fixed wavelengths, so you can measure methane by looking for its absorption lines.

But any Earth-based measurement of Martian methane has to cope with the fact that Earth's atmosphere has far more methane than Mars. How do you separate possible Mars methane absorption lines from Terran ones? There's one clever way: you can measure Mars at quadrature, when it's coming toward us or going away from us, and any methane spectral lines would be red- or blue-shifted compared to the Terran ones. But then the lines overlap with other absorption lines from Earth's atmosphere. It's very difficult to get a reliable measurement. Of course, a measurement from space would avoid those problems, so the spectrograph on the ESA Mars orbiter has been pressed into service. But there are questions about its accuracy.

The published evidence so far for Martian methane just isn't convincing, especially with those unlikely seasonal fluctuations. That doesn't mean there's no methane there; it means we need better data. The next Mars Rover, dubbed "Curiosity", will include a laser spectrometer which can give us much more accurate methane measurements. Curiosity is set to launch this fall and arrive at Mars in August of next year.

It gets worse: the kapton tape issue

But it gets worse. That Curiosity rover whose sensitive equipment is going to answer the question for us? Well, check out an article in Wired last week: Space Duct Tape Could Confuse Mars Rover.

It seems the materials used to build Curiosity, notably the kapton tape used in large quantities to hold the rover together ... emit methane! Andrew C. Schuerger, Christian Clausen and Daniel Britt, in Methane Evolution from UV-irradiated Spacecraft Materials under Simulated Martian Conditions: Implications for the Mars Science Laboratory (MSL) Mission (abstract), take a selection of materials used in the rover, plus bacteria that might be expected to contaminate it, and subject them to simulated Mars conditions. They conclude

... the large amount of kapton tape used on the MSL rover (lower bound estimated at 3 m2) is likely to create a significant source of terrestrial methane contamination during the early part of the mission.

A skeptical eye

So let's sum up:

* We desperately want to see methane on Mars, because it might point to biological processes and that would be cool.
* But we don't currently have any reliable way to measure Martian methane.
* So we build a special mission one of whose primary purposes is to get accurate measurements of Martian methane.
* But we build the probe with materials that will make the measurements unreliable.

It's apparently too late to fix the problem; so instead, just shrug and say, well, it might not be so bad if we measure at night, or if we wait a while (how long?) until most of the methane outgasses. The methane emission from the kapton tape is fairly small -- though it's hard to know exactly how small, since it's impossible to test it in a real Martian environment.

So in a couple of years, when you start seeing news releases trumpeting Curiosity's methane measurements and talking about life on Mars, read them with a skeptical eye.

Maybe Curiosity will see methane levels on Mars so large that they swamp any contamination issues. Maybe not. But we won't be able to tell from the reports we read in the popular press.

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[ 12:38 Mar 13, 2011    More science/astro | permalink to this entry | ]

Sun, 21 Nov 2010

Lunar Water Strip-Mines?

You may have seen the headlines a few weeks ago, when everyone was crowing "Water on the Moon!" after the LCROSS results were finally published. Turns out the moon is wetter than the Sahara (woo!) and all the news sites seemed excited about how we'd be using this for a lunar base. It only takes a ton of rock to get 11-12 gallons of water!

I wondered, am I the only one who thinks 12 gallons isn't very much? I couldn't help envisioning a tiny lunar base surrounded by acres of mine tailing devastation.

So I calculated how much rock it takes to make a ton (assuming basalt; lunar highland anorthosite would be a little less dense). Turns out it's not very much: a ton of basalt would make a cube about 8.6 feet on a side. So okay, I guess it would take quite a while to work up to those acres of devastation. It was an interesting calculation, anyway; rock is a lot less dense than I thought.

You can read the details in my SJAA Ephemeris column this month, Full of Moon.

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[ 19:55 Nov 21, 2010    More science/astro | permalink to this entry | ]

Sat, 06 Feb 2010

Making "Citizen Science" compelling

I had the opportunity to participate in a focus group on NASA's new "citizen science" project, called Moon Zoo, with a bunch of other fellow lunatics, amateur astronomers and lunar enthusiasts.

Moon Zoo sounds really interesting. Ordinary people will analyze high-resolution photos of the lunar surface: find out how many boulders and craters are there. I hope it will also include more details like crater type and size, rilles and so forth, though that wasn't mentioned. These are all tasks that are easy for a human and hard for a computer: perfect for crowdsourcing. Think Galaxy Zoo for the moon. The resulting data will be used for planning future lunar missions as well as for general lunar science.

It sounds like a great project and I'm excited about it. But I'm not going to write about Moon Zoo today -- it doesn't exist yet (current estimate is mid-March), though there is a preliminary PDF. Instead, I want to talk about some of the great ideas that came out of the focus group.

The primary question: How do we get people -- both amateur astronomers and the general public, people of all ages -- interested in contributing to a citizen science project like Moon Zoo?

Here are some of the key ideas:

Make the data public

This was the most important point, echoed by a lot of participants. Some people felt that many of the existing "citizen science" projects project the attitude "We want something from you, but we're not going to give you anything in return." If you use crowdsourcing to create a dataset, make it available to the crowd.

Opening the data has a lot of advantages:

Projects like Wikipedia and Open Street Map, as well as Linux and the rest of the open source movement, show how much an open data model can inspire contributions.

Give credit to individuals and teams

People cited the example of SETI@Home, where teams of contributors can compete to see who's contributed the most. Show rankings for both individuals and groups, so they can track their progress and maybe get a bit competitive with other groups. Highlight groups and individuals who contribute a lot -- maybe even make it a formal competition and offer inexpensive prizes like T-shirts or mugs.

A teenaged panel member had the great suggestion of making buttons that said "I'm a Moon Zookeeper." Little rewards like that don't cost much but can really motivate people.

Offer an offline version

They wanted to hear ideas for publicizing Moon Zoo to groups like our local astronomy clubs.

I mentioned that I've often wanted to spread the word about Galaxy Zoo, but it's entirely a web-based application and when I give talks to clubs or school groups, web access is never an option. (Ironically, the person leading the focus group had planned to demonstrate Galaxy Zoo to us but couldn't get connected to the wi-fi at the Lawrence Hall of Science.)

Projects are so much easier to evangelize if you can download an offline demo.

And not just a demo, either. There should be a way to download a real version, including a small data set. Imagine if you could grab a Moon Zoo pack and do a little classifying whenever you got a few spare minutes -- on the airplane or train, or in a hotel room while traveling.

Important note: this does not mean you should write a separate Windows app for people to download. Keep it HTML, Javascript and cross platform so everyone can run it. Then let people download a local copy of the same web app they run on your site.

Make sure it works on phones and game consoles

Lots of people use smartphones more than they use a desktop computer these days. Make sure the app runs on all the popular smartphones. And lots of kids have access to handheld web-enabled game consoles: you can reach a whole new set of kids by supporting these platforms.

Offer levels of accomplishment, like a game

Lots of people are competitive by nature, and like to feel they're getting better at what they're doing. Play to that: let users advance as they get more experienced, and give them the option of doing harder projects. "I'm up to level 7 in Moon Zoo!"

Use social networking

Facebook. Twitter. Nuff said.

Don't keep results a secret

Quite a few scientific publications have arisen out of Galaxy Zoo -- yet although most of us were familiar with Galaxy Zoo, few of us knew that. Why so secretive? They should be trumpeting achievements like that.

How many times have you volunteered for a survey or study, then wondered for years afterward how the results came out? Researchers never contact the volunteers when the paper is finally published. It's frustrating and demotivating; it makes you not want to volunteer again. Lots of us sign up because we're curious about the science -- but that means we're also curious about the results.

With citizen science projects, this is particularly easy. Set up a mailing list or forum (or both) to discuss results and announce when papers are published. Set up a Twitter account and a Facebook group to announce new papers to anyone who wants to follow. This is the age of Web 2.0, folks -- there's no excuse for not communicating.

I don't know if NASA will listen to our ideas. But I hope they do. Moon Zoo promises to be a terrific project ... and the more of these principles they follow, the more dedicated volunteers they'll get and that will make the project even better.

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[ 20:25 Feb 06, 2010    More science/astro | permalink to this entry | ]

Fri, 18 Sep 2009

A new theory of orbital dynamics

[PGE billboard: Solar Power: Making planets orbit and bagels toast] This PG&E billboard just went up down the street from where I live.
"Solar Power: Making planets orbit and bagels toast."

And here all this time I'd been under the impression that orbits had mostly to do with gravity. Somehow I'd missed the influence of light pressure when writing my orbital software.

Or is the sun's gravitational influence considered a part of "solar power"? Can we look forward to the upcoming generation of gravitovoltaic solar cells?

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[ 20:13 Sep 18, 2009    More humor | permalink to this entry | ]

Sun, 31 May 2009

JS Jup: now, with variable animation speed

I wrote last week about the sorts of programmer compulsions that lead to silly apps like my animated Javascript Jupiter. I got it working well enough and stopped, knowing there were more features that would be easy to add but trying to ignore them.

My mom, immediately upon seeing it, unerringly zeroed in on the biggest missing feature I'd been trying to ignore. "Can you make it go faster or slower?"

I put it off for a while, but of course I had to do it -- so now there are Faster and Slower buttons. It still goes by hour jumps, so the fastest you can go is an hour per millisecond. Fun to watch. Or you can slow it down to 1 hour per 3600000 milliseconds if you want to see it animate in real time. :-)

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[ 11:42 May 31, 2009    More programming | permalink to this entry | ]

Sat, 23 May 2009

Javascript Jupiter

It's a sickness, I tell you.

It's not like I needed another Jupiter's moons application. I've already written more or less the same app for four platforms.

I don't use the Java web version, Juplet, very much any more, because I often have Java disabled or missing. And I don't use my Zaurus any more so Juplet for Zaurus isn't very relevant. But I can always call up my Xlib or PalmOS Jupiter's moons app if I need to check on those Galilean moons. They work fine. Another version would be really pointless. A waste of time.

So it should have been no big deal when, during the course of explaining to someone the difference between Java and Javascript, it suddenly occurred to me that it would be awfully easy to re-implement that Java Juplet web page using Javascript, HTML and CSS. I mean, a rational person would just say "oh, yeah, I suppose that's true" and go on with life.

But what I'm trying to say is that programming isn't a career path, or a hobby, or a field of academic study. It's a disease. It's a compulsion, where, sometimes, just realizing that something could be done renders you unable to think about anything else until you just ... try ... just a few minutes ... see how well it works ... oh, wow, that really looks a lot better than the Java version, wouldn't it look even nicer if you just added in this one other little tweak ... but wait, now it's so close to working, I bet it wouldn't be all that hard to take the Java class and turn it into ...

... and before you know it, it's tomorrow and you have something that's almost a working app, and it's just really a shame to get that far and not finish it at least to the point where you can share it.

But then, Javascript and web pages are so easy to work on that it really isn't that much extra work to add in some features that the old version didn't have, like an animate button ...

... and your Saturday morning is gone forever, and there's not much you can do about that, but at least you have a nice animated Jupiter's moons (and shadows) page when the sickness passes and you can finally think about other things.

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[ 21:10 May 23, 2009    More programming | permalink to this entry | ]

Wed, 01 Apr 2009

Pluto Visits the States

This is a reprinting of an article I wrote for my monthly planet column in the SJAA Ephemeris:

Is Pluto a planet, or not? Maybe you caught the news last month that Illinois, birthplace of Clyde Tombaugh, has declared Pluto a planet. It joins New Mexico, Tombaugh's longtime home, which made a similar declaration two years ago.

When I first heard about the New Mexico resolution, I was told that they had declared that Pluto would be a planet within the state's boundaries. [Size of Pluto and Charon vs. the US] That made me a bit curious: would Pluto even fit inside New Mexico? I looked it up: Pluto has a diameter of 2300km, while New Mexico is about 550km in longitude and a bit more in latitude. Not even close (see Figure 1). Too bad -- I liked the image of Pluto and Charon coming to visit and hang out with friends. Though at Pluto's orbital velocity (it takes it just under 248 years to complete its 18 billion kilometer orbit, meaning an average speed of 23 million km/year or 63,000 km/day) and its current distance of about 32 AU (4.8 billion km), it whould take it about 207 years to get here.

But it turns out that's not what the resolution said anyway. Both states' resolutions said roughly the same thing:

BE IT RESOLVED BY THE LEGISLATURE OF THE STATE OF NEW MEXICO that, as Pluto passes overhead through New Mexico's excellent night skies, it be declared a planet and that March 13, 2007 be declared "Pluto Planet Day" at the legislature.

RESOLVED, BY THE SENATE OF THE NINETY-SIXTH GENERAL ASSEMBLY OF THE STATE OF ILLINOIS, that as Pluto passes overhead through Illinois' night skies, that it be reestablished with full planetary status, and that March 13, 2009 be declared "Pluto Day" in the State of Illinois in honor of the date its discovery was announced in 1930.

So the law applies to anyone (though it's probably not enforceable outside state boundaries) -- but only when Pluto is overhead in New Mexico or Illinois.

But wait -- does Pluto ever actually pass overhead in those states?

New Mexico stretches from 31.2 to about 37 degrees latitude, while Illinois spans 36.9 to 42.4. Right now Pluto is in Sagittarius, with a declination of -17° 41'; there's no way anyone in the US is going to see it directly overhead this year. Worse, it's on its way even farther south. It won't cross into the northern hemisphere until the beginning of 2111. But how far north will it go?

My first thought was to add Pluto's inclination -- 17.15 degrees, very high compared to other planets -- to the 23 degrees of the ecliptic to get 40.4°. Way far north -- no problem in either state! But unfortunately it's not as simple as that.

It turns out that when Pluto gets to its maximum north inclination, it's in Bootes (bet you didn't know Bootes was a constellation of the zodiac, did you? It's that 17° inclination that puts Pluto just past the Virgo border). That'll happen in February of 2228.

But in the Virgo/Bootes region, the ecliptic is 8° south of the equator, not 23° north. So we don't get to add 23 and 17; in fact, Pluto's declination will only be about 7.3° north. That's no help!

To find the time when Pluto gets as far north as it's going to get, you have to combine the declination of the ecliptic and the angle of Pluto above the ecliptic. The online JPL HORIZONS simulator is very helpful for running data like that over long periods -- much easier than plugging dates into a planetarium program. HORIZONS told me that Pluto's maximum northern declination, 23.5°, will happen in spring of 2193.

Unfortunately, 23.5° isn't far enough north to be overhead even from Las Cruces, NM. So Pluto, sadly, will never be overhead from either New Mexico or Illinois, and thus by the text of the two measures, it will never be a planet.

With that in mind, I'm asking you to support my campaign to persuade the governments of Ecuador and Hawaii to pass resolutions similar to the New Mexico and Illinois ones. Please give generously -- and hurry, because we need your support before April 1!

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[ 20:09 Apr 01, 2009    More science/astro | permalink to this entry | ]

Tue, 24 Mar 2009

For Ada Lovelace Day: Vera Rubin

For Ada Lovelace Day I'm honoring Vera Rubin.

In 1948, when she applied to Princeton as an aspiring astronomy grad student, they wouldn't let her in because women weren't allowed. (They finally started admitting women in 1975.) Fortunately, Cornell was more accommodating.

For her thesis, she worked on a project that seemed useful and uncontroversial. She took other people's data on the redshifts of galaxies, and catalogued them to see how fast they were all moving away from us.

Except something unexpected happened. She found that galaxies in one direction weren't moving away as fast as galaxies in the other directions. The universe was supposed to be expanding evenly in all directions -- but that's not what her data showed.

In 1950 she presented her results to a conference of the American Astronomical Society. The results were not promising. Famous astronomers she'd read about but never met stood up in the audience to ridicule her paper and say it couldn't be true. No one would publish her master's thesis. It wasn't a good start to her career. She decided to try to find something less controversial to study.

Her husband finished at Cornell and moved to Washington, D.C.. Rubin and her new baby moved with him, and she enrolled as a PhD student at Georgetown. They had two children by now; her parents watched the kids while she took night classes.

She hooked up with George Gamow at Georgetown. He called her to ask her about her research -- but said they'd have to talk in the lobby, not in his office, because women weren't allowed in the office area of the building.

After Rubin finished her PhD with Gamow in 1954, Her experience trying to present her 1950 paper made her leery of confrontation. She's said, "I wanted a problem that no one would bother me about." Working with Kent Ford at the Carnegie Institute in Washington, she helped design a super-sensitive digital spectrograph, and they set out to make a huge catalog of data on boring "normal" galaxies no one else was looking at. They started with the Andromeda galaxy, M31, the closest large galaxy to us (and the easiest one to see with the naked eye, if you go somewhere away from city lights).

And right away they found something weird. Normally, you'd expect the outer parts of the galaxy to be rotating a lot slower than the inner parts. Think of our solar system: Mercury goes around the sun really fast (a Mercury year is only 88 days), Earth goes not quite as fast, and when you get all the way out to Pluto, it takes 247 years to go around the sun once. It's not just that it has farther to go to make a circuit around the sun; it's that the sun's influence is so weak way out there that Pluto goes a lot slower in its orbit than we do.

Galaxies should be the same way: stars in the center should just whiz around in no time, while stars at the outer edge take forever.

But Rubin and Ford found that Andromeda wasn't like that. When they started looking at the stars farther out, they were all going about the same speed. If anything, the stars at the edge were going a little faster than the stars in the center.

That made no sense. It didn't follow any normal model of gravity or galaxy formation. They published their results in 1970, but no one took them seriously. They decided that maybe something was wrong, or their equipment was faulty. They decided to try studying a simpler problem: just measure the redshift of some faint galaxies and make a catalog of those.

That went well for a while -- except that pretty soon, they ran into the same thing Rubin had discovered as a graduate student back at Cornell. Galaxies in the direction of Pegasus were moving away from us at a different speed from galaxies in other parts of the sky. She and Ford tried again to present that, but the reaction wasn't any more positive this time.

Discouraged, they went back to trying to measure galaxy rotation, hoping Andromeda had just been a fluke. But every galaxy they studied looked the same as Andromeda, with the stars far out near the edge of the galaxy rotating as fast, or faster, than the stars near the hub.

There were only two possible explanations. Either the law of gravity doesn't work the way we think it does ... or there's a lot more matter inside a galaxy than what we see with a telescope.

When they tried to present this result, no one believed it, so they kept measuring more galaxies, always with the same result.

By 1985, they had enough evidence that people finally started paying attention. As their results got talked about more and taken more seriously, they came up with a name for the extra mass that makes the galaxy rotation flat: "dark matter". Yes, the dark matter you hear about that apparently makes up more than 90% of all matter in the universe. Not a bad discovery for someone who was just trying to lay low and catalogue a lot of data that might be useful to other people! (Rubin's first graduate project, on the rotation of the universe, has also since been vindicated.)

Vera Rubin is still working at the Department of Terrestrial Magnetism. Her intellect, hard work and perseverance are an inspiration, and I salute her on Ada Lovelace Day. (You can read other people's Ada Lovelace Day posts in the Ada Lovelace Day Collection.)

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[ 20:12 Mar 24, 2009    More science/astro | permalink to this entry | ]

Tue, 20 Jan 2009

LCA 2009 Tuesday

I missed a lot of the miniconf talks on Tuesday because I wanted to make some last-minute changes to my talk. But I do want to comment on one: Simon Greener's talk on "A Review of Australian Geodata Providers." Of course, I'm not in Australia, but it was quite interesting to hear how similar Australia's problematic geodata siguation is to the situation in the US. His presentation was entertaining, animated and I learned some interesting facts about GPS and geodata in general.

And Dave and I got another good astronomy opportunity with the dark skies at Peppermint Bay at the Speakers' Dinner. Despite occasional intrusive clouds we managed to get a great view of the Large Magellanic Cloud and a decent view of the small one, as well as eta Carinae and the star clouds between Crux and Carina. Pity I'd forgotten to bring my thumpin' travel optics that I'd been using the previous evening: a 6x20 monocular.

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[ 17:15 Jan 20, 2009    More conferences/lca2009 | permalink to this entry | ]

Mon, 19 Jan 2009

LCA 2009 Monday

On day one of LCA 2009, I divided my time between the LinuxChix and Kernel miniconfs.

In the morning, Paul McKenney, in "Why is parallel Programming Hard?", discussed some of the background of parallel programming research, then gave an entertaining demonstration of instruction overhead using a roll of toilet paper. Each square represented one clock cycle -- he estimated there were a few hundred clock cycles in the full roll -- and he had audience members unroll the roll carefully, passing it from one person to the next. It took a long time.

Over at the LinuxChix miniconf, Jacinta Richardson gave a wonderfully entertaining (and useful) talk "On Speaking". She explained how to hack audience members' brains, particularly the corpus callosum and the hippcampus, by using emotion, visual images and suspenseful stories to give your audience whole-brain entertainment.

After Jacinta's talk we spent some time going around the room introducing ourselves, and speakers got a chance to plug their upcoming talks.

I skipped the panel on Geek Parenting (not being a parent) to go back to the kernel miniconf's "Problem Solving Hour". Questions involved network performance, solid state disk performance, how to debug crashes, tracing (the moderator commented that if you're thinking of getting involved in the kernel effort but aren't quite sure what to do, there's a huge need for better tracing and performance analysis tools), solid-state disks (someone plugged the talk on that subject on Friday) and similar interesting topics.

I asked about an overheating problem I've been having with my laptop. I mentioned that even in single-user mode, the CPU temperature keeps going up, so I was pretty sure it was a kernel and not userspace issue. Matthew Garrett said that a lot of drivers are optimized for a normal use case -- meaning X -- and may work very poorly in text mode. You can have something that's overheating in single-user mode, then you start X and a bunch of power management systems kick in and the temperature actually goes down. So how do you figure out what's causing a temperature problem? Open up the laptop when it's hot, poke around then figure out what's hot. Then debug that component.

Lunch was a lovely BBQ provided by Google.

After lunch, Matthew Garrett, in "How I learned to stop worrying and love ACPI", was entertaining, as all his talks are. I'm not sure I actually learned much in the way of practical advice for helping ACPI work better on my machines, but at least I learned lots of new ways in which ACPI sucks more than I ever realized.

Then it was back to LinuxChix for a workshop on getting schoolgirls more interested in IT. We saw short presentations from the four workshop leaders, then split into groups -- our group went outside and sat in the hazy sunshine and talked about how to get girls, teachers, parents and school IT staff on board.

After tea, all the LinuxChix groups reported back on the discussions and there was a full-room discussion on how to get involved with educational programs like that. Then we ended with lightning talks; I got roped into giving one, so I didn't take notes on the rest, but they were all fun and interesting.

Then in the evening, after dinner, we found a spot somewhat sheltered from the lights of the hotel for some quick astronomy before bed. The sky was hazy and picking up lots of sky glow from a light beam shining from the hotel, but fortunately the sky around the Southern Cross was clear. We found both the Large and Small Magellanic clouds, as well as Eta Carina and some other clusters around the Southern Cross. A lovely view, unmatched by anything I saw from around Sydney or Melbourne. Tasmania definitely wins for stargazing!

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[ 05:17 Jan 19, 2009    More conferences/lca2009 | permalink to this entry | ]

Sat, 29 Nov 2008

Upheaval Dome: New research confirms impact theory

Kurt Fisher wrote to draw my attention to the latest Lunar Photo Of the Day (LPOD), a lovely shot he made of one of my favorite places anywhere, Upheaval Dome in Utah's Canyonlands National Park.

Upheaval Dome has long been strongly suspected to be a massive, eroded impact crater, but the LPOD highlights a study that finally puts this (non-)controversy to rest, Elmar Buchner and Thomas Kenkmann's Upheaval Dome, Utah, USA: Impact origin confirmed, documenting shocked quartz grains in the Kayenta sandstone of Upheaval's outer ring.

[Upheaval Dome] It's about time -- it's been pretty clear for many years that this structure was an impact formation, not a collapsed salt dome (the relative lack of salt in the core might have been a clue) but the park service doesn't seem to have gotten the message, giving equal weight to the salt-dome theory in all its Canyonlands literature and signs. Perhaps the Buchner and Kenkmann paper will finally convince them.

Reading about this gave me the push I needed to update my own Upheaval Dome page, adding links to the latest research and to the excellent Upheaval Dome Bibliography Kurt has put together. My page also badly needed a bigger view of the crater itself, so I stitched together a quick panorama of the view from the rim that I'd shot on a trip several years ago but never assembled.

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[ 13:15 Nov 29, 2008    More science/geology | permalink to this entry | ]

Sun, 16 Nov 2008

Cleaning up the edges of Moonroot's transparent images

[moonroot] I wrote moonroot more to figure out how to do it than to run it myself. But on the new monitor I have so much screen real estate that I've started using it -- but the quality of the images was such an embarrassment that I couldn't stand it. So I took a few minutes and cleaned up the images and made a moonroot 0.6 release.

Turned out there was a trick I'd missed when I originally made the images, years ago. XPM apparently only allows 1-bit transparency. When I was editing the RGB image and removing the outside edge of the circle, some of the pixels ended up semi-transparent, and when I saved the file as .xpm, they ended up looking very different (much darker) from what I had edited.

Here are two ways to solve that in GIMP:

  1. Use the "Hard edge" option on the eraser tool (and a hard-edged brush, of course, not a fuzzy one).
  2. Convert the image to indexed, in which case GIMP will only allow one bit's worth of transparency. (That doesn't help for full-color images, but for a greyscale image like the moon, there's no loss of color since even RGB images can only have 8 bits per channel.)

Either way, the way to edit a transparent image where you're trying to make the edges look clean is to add a solid-color background layer (I usually use white, but of course it depends on how you're going to use the image) underneath the layer you're trying to edit. (In the layers dialog, click the New button, chose White for the new layer, click the down-arrow button to move it below the original layer, then click on the original layer so your editing will all happen there.)

Once you're editing a circle with sharp edges, you'll probably need to adjust the colors for some of the edge pixels too. Unfortunately the Smudge tool doesn't seem to work on indexed images, so you'll probably spend a lot of time alternating between the Color Picker and the Pencil tool, picking pixel colors then dabbing them onto other pixels. Key bindings are the best way to do that: o activates the Color Picker, N the Pencil, P the Paintbrush. Even if you don't normally use those shortcuts it's worth learning them for the duration of this sort of operation.

Or use the Clone tool, where the only keyboard shortcut you have to remember is Ctrl to pick a new source pixel. (I didn't think of that until I was already finished, but it works fine.)

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[ 15:48 Nov 16, 2008    More gimp | permalink to this entry | ]

Mon, 20 Oct 2008

Requesting no window decorations (and moonroot 0.4)

Someone on #openbox this morning wanted help in bringing up a window without decorations -- no titlebar or window borders.

Afterward, Mikael commented that the app should really be coded not to have borders in the first place.

Me: You can do that?

Turns out it's not a standard ICCCM request, but one that mwm introduced, MWM_HINTS_DECORATIONS. Mikael pointed me to the urxvt source as an example of an app that uses it.

My own need was more modest: my little moonroot Xlib program that draws the moon at approximately its current phase. Since the code is a lot simpler than urxvt, perhaps the new version, moonroot 0.4, will be useful as an example for someone (it's also an example of how to use the X Shape extension for making non-rectangular windows).

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[ 12:06 Oct 20, 2008    More programming | permalink to this entry | ]

Mon, 22 Sep 2008

Linux Planet: Linux Astronomy part III: Stellarium and Celestia

Part III in the Linux Astronomy series on Linux Planet covers two 3-D apps, Stellarium and Celestia.

Writing this one was somewhat tricky because the current Ubuntu, "Hardy", has a bug in its Radeon handling and both these apps lock my machine up pretty quickly, so I went through a lot of reboot cycles getting the screenshots. (I found lots of bug reports and comments on the web, so I know it's not just me.) Fortunately I was able to test both apps and grab a few screenshots on Fedora 8 and Ubuntu "Feisty" without encountering crashes. (Ubuntu sure has been having a lot of trouble with their X support lately! I'm going to start keeping current Fedora and Suse installs around for times like this.)

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[ 22:10 Sep 22, 2008    More writing | permalink to this entry | ]

Fri, 12 Sep 2008

Linux Planet: Linux Astronomy part II: XEphem

I have a new article on XEphem on Linux Planet, following up to the KStars article two weeks ago: Viewing the Night Sky with Linux, Part II: Visit the Planets With XEphem.

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[ 11:50 Sep 12, 2008    More writing | permalink to this entry | ]

Thu, 28 Aug 2008

Writing for Linux Planet: Stargazing with KStars

I have an article on Linux Planet! The first of many, I hope. At least the first of a short series on Linux astronomy programs, starting with the one that's easiest to use: KStars. It's oriented toward binocular observing, with suggestions for good targets for beginners.

Viewing the Night Sky with Linux, Part I: KStars

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[ 22:46 Aug 28, 2008    More writing | permalink to this entry | ]

Tue, 18 Mar 2008

Setting app name and class in Xlib

I was looking at Dave's little phase-of-the-moon Mac application, and got the urge to play with moonroot, the little xlib ditty I wrote several years ago to put a moon (showing the right phase) on the desktop.

I fired it up, and got the nice moon-shaped window ... but with a titlebar. I didn't want that! Figuring out how to get rid of the titlebar in openbox was easy, just

<application name="moonroot">
    <decor>no</decor>
    <desktop>all</desktop>
</application>
... but it didn't work! A poke with xwininfo showed the likely cause: instead of "moonroot", the window was listed as "Unnamed window". Whoops!

A little poking around revealed three different ways to set "name" for a window: XStoreName, XSetClassHint (which sets both class name and app name), and XSetWMName. Available online documentation on these functions was not very helpful in explaining the differences; fortunately someone hanging out on the openbox channel knew the difference (thanks, Crazy_Hopper). Thus:

I didn't see much in the way of example code for what an app ought to do with these, so I'll post mine here:

    char* appname;
    XClassHint* classHint;
[ ... ]
    if (argv && argc > 1)
        appname = basename(argv[0]);
    else
        appname = "moonroot";

    /* set the titlebar name */
    XStoreName(dpy, win, appname);

    /* set the name and class hints for the window manager to use */
    classHint = XAllocClassHint();
    if (classHint) {
        classHint->res_name = appname;
        classHint->res_class = "MoonRoot";
    }
    XSetClassHint(dpy, win, classHint);
    XFree(classHint);

And if anyone is interested in my silly moon program, it's at moonroot-0.3.tar.gz. moonroot gives you a large moon, moonroot -s gives a smaller one. I'm not terribly happy with its accuracy and wasted too much time today fiddling with it and verifying that it's doing the right time conversions. All I can figure is that the approximation in Meeus' Astronomical Algorithms is way too approximate (it's sometimes off by more than a day) and I should just rewrite all my moon programs to calculate moon phase the hard (and slow) way.

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[ 21:15 Mar 18, 2008    More programming | permalink to this entry | ]

Sun, 28 Oct 2007

Bright naked-eye comet: 17/P Holmes

I finally got a chance to take a look at Comet 17/P Holmes. I'd been hearing about this bright comet for a couple of days, since it unexpectedly broke up and flared from about 17th magnitude (fainter than most amateur telescopes can pick up even in dark skies) to 2nd magnitude (easily visible to the naked eye from light-polluted cities). It's in Perseus, so only visible from the northern hemisphere, pretty much any time after dark (but it's higher a little later in the evening).

And it's just as bright as advertised. I grabbed my binoculars, used a finder chart posted by one of our local SJAA members, and there it was, bright and obviously fuzzy. Without the binoculars it was still easy to see, and still noticably fuzzy.

So I dragged out the trusty 6" dobsonian, and although it has no visible tail, it has lots of structure. It looked like this:
[Comet 17/P Holmes] It has a stellar nucleus, a bright inner area (the coma?) and a much larger, fainter outer halo. There's also a faint star just outside the coma, so it'll be fun (if we continue to get holes in the clouds) to see how fast it moves relative to that star. (Not much motion in the past hour.)

It's nice to have a bright comet in the sky again! Anyone interested in astronomy should check this one out in the next few days -- since it may be in the process of breaking up, there's no telling how long it'll last or what will happen next. Grab some binoculars, or a 'scope if you have one, and take a look.

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[ 22:51 Oct 28, 2007    More science/astro | permalink to this entry | ]

Wed, 08 Nov 2006

Mercury Transits and Titan Occultations

Mercury transited the sun today. The weather forecast predicted rain, and indeed, I awoke this morning to a thick overcast which soon turned to drizzle. But miraculously, ten minutes before the start of the transit the sky cleared, and we were able to see the whole thing, all five hours of it (well, we weren't watching for the whole five hours -- the most interesting parts are the beginning and end).

I had plenty of practice with solar observing yesterday, showing the sun to a group of middle school girls as part of an astronomy workshop. This is organized by the AAUW, the same group that runs the annual Tech Trek summer science girls' camps. (The Stanford Tech Trek has a star party, which is how I got involved with this group.) It's the second year I've done the astronomy workshop for them; this year went pretty smoothly and everybody seemed to have a good time observing the sun, simulating moon phases, learning about the Doppler effect and plotting relative distances of the planets on a road map.

But what I really wanted to write about was the amazing video shown by last weekend's SJAA speaker, Dr. Ivan Linscott of Stanford. As one of the team members on the New Horizons mission to Pluto, he was telling us about Pluto's tenuous atmosphere. There isn't a lot of information on Pluto's atmosphere yet, but one of the goals of New Horizons is to take readings as Pluto occults the sun to see how sunlight is refracted through Pluto's atmosphere.

But that's no problem: it turns out we've already done more challenging occultation studies than that. Back in December 2001, Titan occulted a binary star, and researchers using Palomar's Adaptive Optics setup got a spectacular video of the stars being refracted through Titan's atmosphere as the occultation progresses.

This is old news, of course, but most of us hadn't seen it before and everyone was blown away. Remember, this is a video from Earth, of the atmosphere of a moon of Saturn, something most Earth-based telescopes would have trouble even resolving as a disk. Watch the Titan occultation video here.

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[ 23:38 Nov 08, 2006    More science/astro | permalink to this entry | ]

Fri, 25 Aug 2006

Pluto is too a planet

The BBC had a good article today about the International Astronomical Union vote that demoted Pluto from planet status.

It was fairly obvious that the previous proposal, last week, that defined "planet" as anything big enough that its gravity made it round, was obviously a red herring that nobody was going to take very serious. Fercryinoutloud, it made the asteroid Ceres a planet, as well as Earth's moon (in a few billion years when it gets a bit farther away from us and ceases to be considered a moon).

But apparently there were several other dirty tricks played by the anti-Pluto faction, and IAU members who weren't able to be in the room at the time of the vote are not happy and are spoiling for a rematch. The new definition doesn't make much more sense than the previous one, anyway: it's based on gravitationally sweeping out objects from an orbit, but that also rules out Earth, Mars, Jupiter and Neptune, all of which have non-satellite objects along their orbits.

And of course the public is pretty upset about it for sentimental, non-scientific reasons. Try searching for Pluto or "Save Pluto" on Cafe Press to see the amazing selection of pro-Pluto merchandise you can buy barely a day after the IAU decision. (Personally, I want a Honk if Pluto is still a planet bumper sticker.)

It'll be interesting to see if the decision sticks.

So do I have a viable definition of "planet" which includes Pluto but not Ceres or the various other Kuiper belt objects which are continually being discovered?

Why, no, I don't. But the discussion is purely semantic anyway. Whether we call Pluto a planet doesn't make any difference to planetary science. But it does make a difference to an enormous collection of textbooks, museum exhibits, and other science-for-the-public displays.

Pluto is big enough to have been discovered in 1930, back in the days before computerized robotic telescopes and satellite imaging; it's been considered a planet for 76 years. There's no scientific benefit to changing that, and a lot of social and political reason not to -- especially now with New Horizons headed there to give us our first up-close look at what Pluto actually looks like.

There are two possible bright notes to the Pluto decision. First, Mark Taylor pointed out that it has become much easier to observe all the planets in one night, even with a very small telescope or binoculars.

And second, maybe Christine Lavin will make a new updated version of her song Planet X and go on tour with it.

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[ 22:56 Aug 25, 2006    More science/astro | permalink to this entry | ]

Sun, 10 Jul 2005

Dark Side of the Moon; M51 Supernova

Yesterday was the annual Fremont Peak Star-b-q. This year the weather managed to be fairly perfect for observing afterward: the fog came in for a while, making for fairly dark skies, and it wasn't too cold though it was a bit breezy. It was even reasonably steady.

I had my homebuilt 8" dob, while Dave brought his homebuilt 12.5". Incredibly, we were all alone in the southwest lot: the most Star-b-q was fairly lightly attended, and most of the handful who stayed to observe afterward set up at Coulter row.

The interesting sight of the evening was the supernova in M51 (the Whirlpool galaxy). It was fairly easy in the 12.5" once we knew where to look (Mike Koop came over to visit after looking at it in the 30"), and once we found it there all three of us could see it in the 8" as well.

We had excellent views of Jupiter in the 8", with detail in the red spot, the thin equatorial band easily visible, and long splits in both the northern and southern equatorial bands. I didn't make any sketches since a family wandered by about then so I let them look instead.

We also had lovely low-power views of Venus and crescent Mercury, and we spent some time traversing detail on the dark side of the slim crescent moon due to the excellent earthshine. All the major maria were visible, and of course Aristarchus, but we could also see Plato, Sinus Iridum, Kepler, Copernicus and its ray system, Tycho (only in the 12" -- the 8" was having glare problems that close to the lit part of the moon) and one long ray from Tycho that extended across Mare Nubium and out to near Copernicus. Pretty good for observing the "dark" side!

Neither of us was able to find Comet Tempel-1 (the Deep Impact comet), even with the 12.5". But after moonset I picked up the Veil and North American in the 8" unfiltered (having left my filters at home), and we got some outstanding views of the nebulae in Sagittarius, particularly the Trifid, which was showing more dust-lane detail without a filter than I've ever seen even filtered.

It was a good night for carnivores, too. We saw one little grey fox cub trotting up the road to the observatory during dinner, and there was another by the side of the road on the way home. Then, farther down the road, I had to stop for three baby raccoons playing in the street. (Very cute!) They eventually got the idea that maybe they should get off the road and watch from the shoulder. The parents were nowhere to be seen: probably much more car-wise than their children (I don't often see raccoon roadkill). I hope the kids got a scolding afterward about finding safer places to play.

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[ 23:31 Jul 10, 2005    More science/astro | permalink to this entry | ]

Fri, 17 Jun 2005

The Game of Telephone

Remember the game of "Telephone" when you were a kid? Everybody gets in a big circle. One kid whispers a message in the ear of the kid next to them. That kid repeats the message to the next kid, and so on around the circle. By the time the message gets back to the originator, it has usually changed beyond recognition.

Sometimes the Internet is like that.

Background: a year and a half ago, in August 2003, there was an unusually favorable Mars opposition. Mars has a year roughly double ours, so Mars "oppositions" happen about every two years (plus a few months). An opposition is when we and Mars are both on the same side of the sun (so the sun is opposite Mars in our sky, and Mars is at its highest at midnight). We're much closer to Mars at opposition than at other times, and that makes a big difference on a planet as small as Mars, so for people who like to observe Mars with a telescope, oppositions are the best time to do it.

The August 2003 opposition was the closest opposition in thousands of years, because Mars was near its perihelion (the point where it's closest to earth) at the time of the opposition. Much was made of this in the press (the press loves events where they can say "best in 10,000 years") to the point where lots of people who aren't normally interested in astronomy decided they wanted to see Mars and came to star parties to look through telescopes.

That's always nice, and we tried to show them Mars, though Mars is very small, even during an opposition. The 2003 opposition wasn't actually all that favorable for those of us in northern hemisphere. because Mars was near the southernmost part of its orbit. That means it was very low in the sky, which is never good for seeing detail through a telescope. Down near the horizon you're looking through a lot more of Earth's atmosphere, and you're down near all the heat waves coming off houses and streets and even rocks. That disturbs the view quite a bit, like trying to see detail on a penny at the bottom of a swimming pool.

This year's opposition, around Halloween, will not be as close as the 2003 opposition, but it's still fairly close as oppositions go. Plus, this year, Mars will be much farther north. So we're expecting a good opposition -- weather permitting, both on Earth, which is sometimes cloudy in November, and on Mars, where you never know when a freak dust storm might appear.

Which brings me back to the game of Telephone.

A few weeks ago I got the first of them. An email from someone quoting a message someone had forwarded, asking whether it was true. The message began:

The Red Planet is about to be spectacular! This month and next, Earth is catching up with Mars in an encounter that will culminate in the closest approach between the two planets in recorded history.
and it ended:
Share this with your children and grandchildren. NO ONE ALIVE TODAY WILL EVER SEE THIS AGAIN
(sic on the caps and the lack of a period at the end).

I sent a reply saying the email was two years out of date, and giving information on this year's Mars opposition and the fact that it may actually be better for observing Mars than 2003 was. But the next day I got a similar inquiry from someone else. So I updated my Mars FAQ to mention the misleading internet message, and the inquiries slowed down.

But today, I got a new variant.

Subject: IS MARS GOING TO BE AS BIG AS THE MOON IN AUGUST?

As big as the moon! That would be a very close opposition!

(Dave, always succinct, said I should reply and say simply, "Bigger." Mars is, of course, always bigger than the moon, even if its apparent size as viewed from earth is small.)

It looks like the story is growing in the telling, in a way it somehow didn't two years ago.

I can't wait to see what the story will have become by August. Mars is going to hit us?

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[ 11:48 Jun 17, 2005    More science/astro | permalink to this entry | ]

Mon, 17 Jan 2005

Open Source Scientific Image Processing

Anthony Liekens has a wonderful page on open-source Cassini-Huygens image analysis.

A group of people from a space IRC channel took the raw images from the descent of the Huygens probe onto Titan's surface, and applied image processing: they stitched panoramas, created animations, created stereograms, added sharpening and color. The results are very impressive!

I hope NASA takes notice of this. There's a lot of interest, energy and talent in the community, which could be very helpful in analysis of astronomical data. Astronomy has a long history of amateur involvement in scientific research, perhaps more so than any other science; extending that to space-based research seems only a small step.

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[ 19:30 Jan 17, 2005    More science/astro | permalink to this entry | ]

Sun, 18 Jul 2004

FPOA Star-b-q

Hiking up to the top of Fremont Peak before the FPOA Star-b-q started, we saw the Ghost and the Darkness, squirrel style. A couple of ground squirrels hidden in the tall grass startled as we walked by, and whisked off through the grass, occasionally twitching a tail-tip up above the tops of the grasses but otherwise mostly invisible.

Down in the parking lots, there were some interesting ant or wasp-like insects: furry scarlet head, black thorax, furry scarlet abdomen. The wings were black, too, and they could fly at least a little. No idea what they were.

Learned a new word reading scoops on the way down: Anecdotage, that advanced age where all one does is relate stories about "the good, old days."

Turned out Jeff Moore was the speaker at FPOA. He always gives good talks, but this one was especially good: interpretation of the Mars Rover geologic results so far. Some of his slides showed terrestrial scenes (mostly Death Valley) for comparison with the Martian geologic features, and he mentioned that the terrestrial slides were easy to tell because they were the ones with the pocketknife showing (for scale). So the following morning, I got inspired to whip up a few counterexamples.

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[ 10:00 Jul 18, 2004    More science/astro | permalink to this entry | ]