Shallow Thoughts : tags : moon

How to Extend a Moonrise

Last night, as we drove home from the Pumpkin Glow -- one of Los Alamos's best annual events, a night exhibition of dozens of carved pumpkins all together in one place -- I noticed a glow on the horizon right around Truchas Peak and wondered if the moon was going to rise that far north.

Sure enough, I saw the first sliver of the moon poking over the peak as we passed the airport. "We may get an extended moonrise tonight", I said, realizing that as the moon rose, we'd be descending the "Main Hill Road", as that section of NM 502 is locally known, so we'd get lower with respect to the mountains even as the moon got higher. Which would win?

As it turns out, neither. The change of angle during the descent down the Main Hill Road exactly matches the rate of moonrise, so the size of the moon's sliver stayed almost exactly the same during the whole descent, until we got down to the "Y" where a nearby mesa blocked our view entirely. By the time we could see the moon again, it was just freeing itself of the mountains.

Neat! Made me think of The Little Prince: his home asteroid B6-12 (no, that's not a real asteroid desgination) was small enough that by moving his chair, he could watch sunset over and over again. I'm a sucker for moonrises -- and now I know how I can make them last longer!

Tags: moon, moonrise
[ 19:32 Oct 28, 2018    More science/astro | permalink to this entry | ]

Lunar eclipse animations

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

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

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

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

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

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

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

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

Tags: astronomy, eclipse, moon, gimp
[ 12:55 Oct 01, 2015    More science/astro | permalink to this entry | ]

Mad Moon Models

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

Last month I stumbled upon a loony moon book I hadn't seen before, one that deserves consideration by all lunar observers.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Here are some places to get it:
Amazon:

• The basic paperback version I got. Has all the scans, but some of them are poor
• Another paperback version
• A hardcover version

Online:

• HTML version at http://atschool.eduweb.co.uk
• Archive.org -- has epub, Kindle and other formats
• Google Books

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

Tags: astronomy, moon, science, art, books
[ 16:12 Jul 03, 2013    More science/astro | permalink to this entry | ]