Shallow Thoughts : : science

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

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 | ]

Mon, 06 Apr 2020

F is for Food Waste

I keep seeing people claim that 40% of consumer food in the US is thrown away uneaten, or hear statistics like 20 pounds of wasted food per person per month.

I simply don't believe it.

There's no question that some food is wasted. It's hard to avoid having that big watermelon go bad before you have a chance to finish it all, especially when you're a one- or two-person household and the market won't sell you a quarter pound of cherries or half a pound of ground beef. And then there's all the stuff you don't want to eat: the bones, the fat, the banana peels and apple cores, the artichoke leaves and corn cobs.

But even if you count all that ... 40 percent? 2/3 of a pound per day per person? And that's supposed to be an average -- so if Dave and I are throwing out a few ounces, somebody else would have to be throwing out multiple pounds a day. It just doesn't seem possible. Who would do that?

When you see people quoting a surprising number -- especially when you see the same big number quoted by lots of people -- you should always ask yourself the source of the number.

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[ 20:08 Apr 06, 2020    More science | 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 | ]