Fremont Peak on 6/27: a green flash from the moon
By Akkana Peck

I almost didn't go up to the Peak on Saturday. Seen from down below, the thick fog looked like it was almost up to the level of the Peak, and I thought it was going to cover the peak and ruin the evening. But David thought it didn't look that bad and it was worth trying, so we drove up anyway.

A good thing! I'd been hearing for years about those magic nights when the fog covers the lights of the towns below, leaving the Peak in darkness; but in the couple of years I've been observing there, the weather patterns have been unusual, apparently, and I'd never seen it. Saturday night was one of those nights, with a warm inversion layer; it was cold and windy down in San Juan Bautista, but the Coulter parking lot was warm enough that I never bothered to put gloves on (which is saying something, since my hands get cold very easily).

I had my Cave 6" f/8, which I was trying for the first time on my GP mount. I had tried this combination in daytime (focusing at 300x on the tiles of the building across the street from my driveway) and it seemed unacceptably jiggly, but I wanted to try it in astronomical use to see if it was usable. The GP is much more portable than the Cave's beefy german equatorial pier-mount-on-wheels. As it turned out, it was indeed shaky, needing a long settle time after focusing, and might not be usable in high winds, but in the calm weather on Saturday, it was quite usable.

The southwest lot was completely packed with cars, so we headed to Coulter. We parked just in time to miss a nice green flash, the other observers informed us. I could have seen it had I just turned around in time. Oh, well.

The crescent moon was visible at sunset, so that was my first target. The seeing wasn't very steady, low on the horizon where the moon was, but still, some of the craters and small mountains near Crisium made for a nice view. Mercury, a bit below the moon, was also visible, as a small rainbow disk. The moon was showing quite a bit of earthshine, but I heard my sandwich calling me from the car and didn't try looking for any particular features. But then someone called out that a star was about to be occulted, and I returned to the eyepiece in time to see the star disappear behind the dark limb. Very pretty!

After eating, I wandered over to Coulter Row and discovered that Orion had set up a large collection of demo scopes, and someone was giving a talk on how to use digital setting circles on a dob. I didn't join the crowd listening to the talk, but instead wandered around sampling views through the various 'scopes they had, including a Vixen 80 Fluorite (turned on the moon at very low power, perhaps 60x; at that power, it was nice and sharp and showed very little color, only a hint of green near the limb; I wondered how it would do at higher magnification), a Celestron FirstScope 80 (at least, I think that's what it was; it gave a nice image, at a somewhat higher magnification than the Vixen was showing, with a fair amount of purple haze on the limb, as one would expect from an achromat, but still, a perfectly acceptable image), and a 102 ED, a new 'scope, which looked very short -- I wasn't able to find out what the focal ratio was, but I might guess it to be f/6 or even slightly shorter. The ED had a much shorter eyepiece and was showing a higher power view of the moon; it was surprisingly dim, and the whole image seemed very green compared to the other 'scopes, though it had very little color error on the limb of the moon. Seemed like an interesting 'scope, and it would have been fun to see them set up all showing views at similar magnification to see how they all compared to each other. They also had a couple of dobs, a 102F (which wasn't pointed at anything -- the mount was having drive problems) and I think a normal 102, a few binoculars and some SCTs, but I didn't look through any of those.

I wandered back to my setup, now that it was dark (the low crescent moon wasn't hurting the sky much) and puttered around looking at Messier objects for a while, then had my attention called to the setting moon. As it sank lower and lower toward the horizon, it was apparently passing through many different laminar layers of atmosphere, and the shape was weirdly distorted, with the limb showing significant hills and valleys which would slowly move up along the limb as the moon sank through each layer in turn. Several of us ended up sitting in odd contorted positions trying to rest our binoculars on knees or logs to hold it steady enough to get a good view of its changing shape. Finally, the lower horn of the crescent disappeared behind the invisible horizon, and the rest of the crescent rapidly followed. The horizon's cutoff line was so sharp that we wondered whether it might be possible to get a green flash off the moon. So we watched, as the upper horn reached the horizon, and flattened out -- and then hovered there, turning less and less red until finally it was, indeed, almost greenish. A green flash from the moon! I'd never heard of such a thing before.

Now it truly was dark. I looked for the Veil with binoculars; the northeastern loop was fairly easy in my 8x42 Ultraview, while the part around 51 Cygni was more difficult. I tried the 6": both sections, and a few of the inner bits, were easy to see, but I couldn't see any filamentary structure. I think I remember seeing filaments before with the 6"; I think the seeing may not have been terribly steady, even though the darkness was quite impressive. I had a similar reaction to M82; both M81 and M82 stood out like beacons (I was surprised when moving to them at how easy it was to see M81 in my 6x30 finder) but the dark lanes in M82 were hard to make out, much less clear than I remember seeing them on other nights. Going back to the binoculars, the North American nebula was much more obvious than I'm used to -- the whole continent could be seen -- as well as a vague indication of the Pelican.

I continued going after bright objects, the clusters and nebulae in Scorpius and Sagittarius. In a 15 Panoptic (80x), the Lagoon (M8) showed more nebulosity than I'd ever seen before. Curious whether there might be yet more to be seen, I added a UHC filter, and sure enough, I saw even more! The nearby Trifid, Swan, and Eagle all showed equally amazing views. I made sketches of the Eagle (http://www.best.com/~akkana/images/astro/m16.jpg) and the Lagoon (http://www.best.com/~akkana/images/astro/m8.jpg) to add to my sketch page (http://www.best.com/~akkana/sketch.html).

Just before I began on the M8 sketch, a nearby observer came over to look, and pointed out the diagonal striations in the nebulosity just above the dark lane, which I hadn't noticed. We checked in a C11, and the striations were very obvious there (much more so than in my 6").

Alas, all too soon I looked at my watch and discovered that it was past midnight, and I'd set a curfew for myself of 11:30 since I'm recovering from a bad cold. So reluctantly, I packed up, wishing I could stay to enjoy the rest of the night. On the way home, I kept an eye out for what I was missing; from the car, I could see M31, naked eye, and Jupiter rising. I'll have to say hello to them next time.