Moon: Hypatia Ray, Sunrise in Clavius, and Other Views

1998 Mar 4-8

Last week, northern California finally got a reprieve from the continually cloudy El Nino weather, just in time for the good March lunation. We got clear skies every other night -- Wednesday, Friday, and Sunday -- with rain on the intervening nights. So we didn't get to see the whole lunation, but at least we saw some nice bits of it.

Wednesday, March 4, was the best seeing. While looking (in a C-8) for Rimae Hypatia (which turned out to be obvious), I stumbled across a new sunrise ray I'd never seen mentioned before. Hypatia has a break in its eastern wall, and at about 8pm PST, a thin ray was just beginning to spill through the gap in the wall and all the way across the crater floor to the other side, where another break in the wall, just south of where the ray ended, created a second ray streaming out of Hypatia onto the terrain west of the crater. It was a lovely sight -- the best lunar ray I've observed so far.

Also showing were the double rings around Mare Nectaris: the Altai Scarp and the walls of Theophilus/Cyrilius/Catharina make a double ring of mountains rather like the double ring around Orientale, except that only half of it is readily visible. This is the best chance we earthbound observers get to see "live" something like what Orientale looks like face-on in the spacecraft pictures.

South of Plinius, Rimae Plinius split the south end of Dorsa Smirnov like the cracks across the Mid-Atlantic Ridge here on earth, and I noticed a perfect little dome which turned out to be Arago alpha, with its companion dome beta (larger but less symmetrical) nearby. Near Janssen, an odd crater looked like a deer hoofprint; it's labelled HB and H on Rukl chart 67 (but is that Janssen HB, Dove HB, Lockyer HB, or what? I wish Rukl were clearer about such things).

Friday, March 6: I took my 80mm Vixen to a public star party in San Jose. A large crater near the south end of the terminator caught my eye: still in darkness, it contained two smaller craters the tips of whose outer rims were just barely beginning to catch the sunlight. Fainter streamers connected the two craters, and as I occasionally glanced at it over the next half hour in various telescopes, these lit streamers gradually changed angle. Fascinating. Eventually things calmed down enough for me to get out my copy of Rukl and crater-hop from the Straight Wall to the crater in question to discover that it was ... Clavius! I hadn't recognized it because only two of its interior craters were visible, but as I continued to watch, emerging gradually into the light was the south rim of a third crater in the arc of five that makes Clavius so easily recognizable when fully lit. Robin Casady's CCD image (he posted a link this morning) also captures this sunrise -- apparently half an hour to an hour later than my later sketch -- very nicely.

I stole some time to make a quick pen sketch, which I later turned into pencil and charcoal sketches of two points of the Clavius sunrise: (pencil) and (charcoal).

Sunday, March 8, the seeing was quite a bit worse, but the view still looked nice in the 80mm. Sinus Iridium had just emerged into full sun (too bad -- this is another area which is really fascinating to watch as the sun rises over it, and I've only caught that once and was hoping to see it again. Next month ...) and I became fascinated with a capital "A" lying just south of there. Rukl shows it clearly: Dorsum Bucher at the bottom of chart 9. A bit farther south, the Harbinger Mountains were just sticking the tips of their peaks into the light, and looked amazingly white, almost snow-capped, in the surrounding darkness. Otherwise, the seeing wasn't good enough to do much rille-hunting, but the domes near Copernicus were showing nicely.

Three clear nights in the same week! Whooee! (Sorry, I'm better now. :-)

Akkana Peck ; last updated: 1998 Mar 9