Shallow Thoughts : tags : astronomy

Saw the "Ring of Fire" 2012 annular eclipse

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

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. 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.

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.

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 --

• The mother with medical problems, obviously feeling quite poorly but still bringing her husband and son out for repeated views.
• the woman who said she didn't want to be in the sun because she'd been drinking too much by the pool.
• The family where Dad kept looking through paper glasses the kids insisted was a "3-D viewer". Alarmed, we took a look, and found it was a perfectly reasonable eclipse viewer marked SAFE FOR SOLAR VIEWING. Whew!
• The teen girl who kept looking directly at the sun despite everyone telling her not to ... I hope she didn't damage her vision.
• The kid who wanted to borrow my binocular to look at some birds circling in the distance. I wanted to let him, but with all the attention on the sun I was too nervous, so instead I changed the subject and showed him how to identify turkey vultures (wings in a V, tipping from side to side) even without binoculars).
• The man who sat in a parking space near us reading a catalog, telling us repeatedly he was just reading his catalog. When Dave insisted he come and take a look, he looked in the eyepiece for about ten seconds, then looked Dave in the eye and informed him solemnly that he was just reading his catalog.
• The family who'd been instructed by their grandmother, in the hospital awaiting an operation, to watch the eclipse and bring back pictures for her. I hope they got some decent ones!

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.

Tags: astronomy, science, eclipse, travel
[ 10:42 May 22, 2012    More science/astro | permalink to this entry | comments ]

Ring of Fire: 2012 annular eclipse

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.

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.

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.)

Tags: astronomy, science, eclipse
[ 20:12 May 16, 2012    More science/astro | permalink to this entry | comments ]

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.

Tags: astronomy, programming, python
[ 13:44 Apr 27, 2012    More science/astro | permalink to this entry | comments ]

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.

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.

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.

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.

Tags: analemma, astronomy, science, programming, python, writing
[ 19:54 Dec 29, 2011    More science/astro | permalink to this entry | comments ]

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.

Tags: astronomy, science, programming, python, writing
[ 10:28 Dec 22, 2011    More science/astro | permalink to this entry | comments ]

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.

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!

Tags: astronomy, sketching, gimp
[ 14:13 Jun 07, 2011    More science/astro | permalink to this entry | comments ]

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.

Tags: astronomy, mars, science
[ 11:38 Mar 13, 2011    More science/astro | permalink to this entry | comments ]

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:

• People can make "mashups", useful sites that display your data in useful ways or combine it with other data. This can generate more interest in your project and more contributors.
• School groups can work on class projects or science fair projects, probably contributing more data along the way.
• It might help the next generation of scientist get started.
• It shows openness and good faith: witness the recent blow-up over the leaked IPCC emails and the debate over how much climate data has been kept private.

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.

Tags: science, astronomy, open source, crowdsourcing
[ 19:25 Feb 06, 2010    More science/astro | permalink to this entry | comments ]

A new theory of orbital dynamics

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?

Tags: humor, astronomy
[ 19:13 Sep 18, 2009    More humor | permalink to this entry | comments ]

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. :-)

Tags: programming, astronomy, javascript
[ 10:42 May 31, 2009    More programming | permalink to this entry | comments ]

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.

Tags: programming, astronomy, javascript
[ 20:10 May 23, 2009    More programming | permalink to this entry | comments ]

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. 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!

Tags: science, astronomy, pluto, humor, writing
[ 19:09 Apr 01, 2009    More science/astro | permalink to this entry | comments ]

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.)

Tags: AdaLovelaceDay09, chix, astronomy
[ 19:12 Mar 24, 2009    More science/astro | permalink to this entry | comments ]

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.

Tags: lca2009, linux.conf.au, astronomy, mapping
[ 16:15 Jan 20, 2009    More conferences/lca2009 | permalink to this entry | comments ]

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!

Tags: lca2009, linux.conf.au, astronomy
[ 04:17 Jan 19, 2009    More conferences/lca2009 | permalink to this entry | comments ]

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.

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.

Tags: geology, astronomy, trails, impact crater
[ 12:15 Nov 29, 2008    More science/geology | permalink to this entry | comments ]

Cleaning up the edges of Moonroot's transparent images

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.)

Tags: programming, astronomy, gimp
[ 14:48 Nov 16, 2008    More gimp | permalink to this entry | comments ]

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).

Tags: programming, xlib, astronomy, window managers
[ 11:06 Oct 20, 2008    More programming | permalink to this entry | comments ]

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.)

Tags: writing, astronomy, linux, ubuntu, bugs
[ 21:10 Sep 22, 2008    More writing | permalink to this entry | comments ]

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.

Tags: writing, astronomy, linux
[ 10:50 Sep 12, 2008    More writing | permalink to this entry | comments ]

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

Tags: writing, astronomy, linux
[ 21:46 Aug 28, 2008    More writing | permalink to this entry | comments ]

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:

• XSetWMName sets a property called XA_NAME which is primarily used to update the window's titlebar. Note that this may be more than the app name (for instance, Firefox puts the title of the current page in the titlebar). To use XSetWMName, you have to set up and populate an XTextProperty structure, which first requires that you set up a string list then run XStringListToTextProperty -- not difficult but it's several annoying steps.
• XStoreName is a shortcut to XSetWMName, a way to set the XA_NAME (titlebar name) in one step.
• XSetClassHint sets two properties at once: a name hint and a class hint. This is the name and class that the window manager uses for directives like suppressing the titlebar.

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.

Tags: programming, xlib, astronomy
[ 20:15 Mar 18, 2008    More programming | permalink to this entry | comments ]

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:
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.

Tags: science, astronomy
[ 21:51 Oct 28, 2007    More science/astro | permalink to this entry | comments ]

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.

Tags: science, astronomy
[ 22:38 Nov 08, 2006    More science/astro | permalink to this entry | comments ]

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.

Tags: science, astronomy
[ 21:56 Aug 25, 2006    More science/astro | permalink to this entry | comments ]

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.

Tags: science, astronomy
[ 22:31 Jul 10, 2005    More science/astro | permalink to this entry | comments ]

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?

Tags: science, astronomy
[ 10:48 Jun 17, 2005    More science/astro | permalink to this entry | comments ]

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.

Tags: science, astronomy
[ 18:30 Jan 17, 2005    More science/astro | permalink to this entry | comments ]

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.

Tags: science, astronomy
[ 09:00 Jul 18, 2004    More science/astro | permalink to this entry | comments ]