Shallow Thoughts : : science Akkana's Musings on Open Source Computing and Technology, Science, and Nature.

Sat, 25 Jul 2020

S is for 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 | comments ]

Thu, 16 Jul 2020

Comet C/2020 F3 NEOWISE in the evening sky 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 | comments ]

Sat, 11 Jul 2020

Sat, 20 Jun 2020

Solstice Sun Dagger Today is the summer solstice. Happy solstice! 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 | comments ]

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 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 | comments ]

Sun, 01 Mar 2020

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

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.



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

Tue, 10 Dec 2019

Planetarium Show Friday: Hitchhiker's Guide to the Moon This Friday, Dave and I will be presenting a planetarium show called The Hitchhiker's Guide to the Moon: Visit the Moon Without Leaving Your Home Planet. I'm jazzed about this show. I think it'll be the most fun planetarium show we've given so far. We'll be showing a variety of lunarfeatures: maria, craters, mountains, rilles, domes, catenae and more. For each one, we'll discuss what the feature actually is and how it was created, where to see good examples on the moon, and -- the important part -- where you can go on Earth, and specifically in the Western US, to see a similar feature up close. Plus: a short flyover of some of the major features using the full-dome planetarium. Some features, like Tycho, the Straight Wall, Reiner Gamma, plus lots of rilles, look really great in the planetarium. If you can't get to the moon yourself, this is the next best thing! The Hitchhiker's Guide to the Moon: 7pm at the PEEC nature center. Admission is free. Come find out how to explore the moon without leaving your home planet!



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

Mon, 11 Nov 2019