Moon ORs: Feb 27th and March 2nd, 2004

by Marek Cichanski

BTW, nice drawing of J. Herschel, Mark! It definitely gets across the "moat-like foot of inner rim" appearance that many people have noticed.

For the record, here are the ORs:

Near-perfect first quarter moon. Terminator is dead on the middle of Aristillus, at longitude 1 deg E.

Nice color contrast on Palus Somnii, with the sun-facing rim of Proclus bright white.

Lots of "pebbly" ejecta around Vallis Alpes. The valley's floor is in shadow, its NW wall is brightly lit.

Montes Caucasus are spectacular under this illumination. The highest peak is just E of the crater Callipus. In fact, this "high peak" is the E rim of the crater Calippus C. This is wild -- the highest point in the mountain range (apparently) is the rim of a half-gone crater. How did the W half of the crater get torn away? Landsliding? Faulting? Collapse during inundation by Imbrium mare lava? Weird.

Montes Caucasus are casting long shadows across eastern Mare Imbrium. Very jagged and dramatic. I'm fairly ignorant about the history of the naming of lunar features, but I wonder how they picked the names of the mountain ranges? Why was one range named for the Caucasus and one for the Alps, say? The lunar Caucasus are sort of the farthest major range to the west (or east, in the old days of the 'astronomical convention'.) I wonder if they could have been viewed as a bridge between East and West, much like the terrestrial Caucasus form a dividing range between Europe and Asia? Maybe I'm just reading too much into it.

Theh Caucasian promontory W of the crater Lamech is casting an incredibly dark shadow. It has a perfectly crater-like, ellipsoidal shape. Looks just like a crater with no rim. Almost looks like artificial, or like a shadow cast by a satellite of the moon (if it had any), a la the Galilean satellites' shadows on Jupiter.

Tried for Rima Calippus, but didn't quite get it.

Alexander - yes, it's a 'walled plain', but I'm skeptical that it was ever a crater.

Rima Theatetus look(s) an awful lot like a wrinkle ridge to me. I fact, it/they look a lot like a west-facing 'flow front', caused by Serenitatis lava flowing W-ward out onto older Imbrium lava plains. could just be a trick of the illumination, though. Would be curious to check out some stereo Lunar Orbiter imagery of this feature.

Albategnius is just beautiful tonight. The floor looks impeccably smooth and 'maria grey', slightly darker in the NE quarter. Hard to tell if that's just illumination. The central peak ("alpha") is casting a beautiful shadow across the floor, with its tip just touching the rim of the crater Klein, right at the craterlet Klein A. Beautiful! E rim of Albategnius is casting a great "ripsaw ridge" shadow onto the crater's lava-flooded floor. The mountain ridge that's casting the shadow is probably not nearly so jagged as the shadow suggests, but it's fun to think of it that way. I once saw a ridge in the North Cascades called Ripsaw Ridge that looked like this shadow. The Sierra has numerous crests like it, too, such as the Koip Crest and the Matthes Crest.

Great Imbrium sculpture in the area around Albategnius. Many clefts and catenae.

Mons Piton is a blazing white in a sea of darkness. Ain't nothing finer.

Area around the crater Walter (Rukl 65): Awesome age relationships between craters, around the crater Stofler.

7 Nag w/ 2x barlow: Rimae Ariadeus, Hyginus, and Triesnecker showing up very nicely. Hyginus shows numerous irregularities in width, and in places appears to be a chain of craters.

Tried for the small craters Triesnecker F and G, got fleeting hints, but couldn't quite get 'em, even with the 5 Nag and the Barlo (240x). Hyginus A is very distinct, though. You really can drive this 80mm scope up to 240x if you really have to. Amazing.

The plateau north of Godin C is funky. Very distinct topographic feature. Dark in color - the summit plateau may be a bit concave.

Before observing the moon, I looked at Saturn, Rigel, and M42. All were nice, as always.

Crater J. Herschel has a terra-like (i.e. non-lava) floor. Not obviously flooded by any mare material. Floor looks domed, or maybe inner edges of rim are "moat-like". Rim is low, soft, much eroded. Horrebow and Horrebow A are a nice double crater on the S edge of J. Herschel. I forget where William Herschel's crater is, but it's always nice to see features named for the ol' Herschel clan. I don't know why, but as the months have gone by since my visit to the Herschel museum in Bath, England, my admiration for them has just grown and grown. I keep thinking of that old-school alt-az scope in the foyer, the relatively limited view of the sky from their back garden, the cloudy weather, and I say to myself "William Herschel was the MAN." John wasn't no slouch, neither. All the way down to the Cape to catalog the southern sky. As a scientist son who's followed in his father's footsteps, I gotta give John Herschel a shout-out.

Always in search of new 'games' to play while observing the moon, I thought of this one tonight. Pick a type of crater illumination, and look for all the craters that show that illumination. Tonight, I decided to look for all of the craters that showed "classic near-terminator illumination" (floor dark, sun-facing inner rim brightly lit). Tonight, around 20:30-21:30 PST, I the following craters showed it:

Harpalus, Foucault, Sharp, Mairan, Gruithuisen, Aristarchus, Marius A, B, C, Suess, Suess B, D (these three make a beautiful trio of craters near the terminator tonight), Flamsteed, Flamsteed B, C, Letronne A, Mersenius, Mersenius C and S, Liebig, many craters in and around Lacus Excellentiae (Clausius, etc...), Noggerath, Zuchius, Bettinus, Kircher.

Notable features tonight:

The usual "pebbly" ejecta N and W of Sinus Iridum.

Gruithuisen domes, and small plateaus near them. Beautiful!

Montes Harbinger, sticking up above the mare plains. The W-most mountains look like domes.

Krieger, Wollaston, and a small mountain between them were casting long, pointy shadows across the mare. The tips of the shadows were touching the terminator earlier this evening.

Wrinkle ridges N and S of the Aristarchus plateau, and S of crater Marius.

Gassendi, clefts in western Mare Humorum.

Incredibly lumpy terrain to the SW of Mare Humorum. Craters and huge lumpy mountains. Remarkable! Area south of Fourier A.

Doppelmayr, a beautiful, mostly-ruined crater. I wonder if the NE side was always lower than the other parts of the rim, allowing lava to overrun it, or did the lava cause the NE side to collapse?

Lacus Excellentiae - another neat "lake". Very irregular margin - not really much of a margin at all. Lava flooding of an irregular area of craters and lumpy ejecta.

Hainzel, Schiller - elongated double craters.

Eastern outer wall of the large walled plain Schickard is in view, but interior is dark. Crater Drebbel has "classic" illumination.

The tip of the central peak of the crater Bettinus is lit, and is seen against the shadowed interior of the crater. This effect is even more spectacular when the crater in question is near the limb.

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Posted on sf-bay-tac Tue Mar 2 23:55:04 2004 PT
Converted by report.pm 1.0 Fri Mar 12 22:07:38 2004 PT