by Marek Cichanski
But within five minutes of arriving at work, with my umbrella dripping and my lower pant legs and shoes wet, I knew I was going to be looking at lunar domes tonight.
Why? Because I could see that the back end of the storm was nearly upon us. (I was looking at the NWS IR loop.) Puffy clouds and a fair amount of clear air were following right behind. Granted, the puffy clouds were a sign of instability, and thundershowers were a distinct possibility, but I had a feeling we'd get a fair amount of clear sky tonight. Probably some pretty wobbly seeing, but at least a fair amount of clear.
Took the bus home, opened up the garage, pulled the car out, and set up my M603. I saw that the moon was in the clear, and I popped in the 16 Nag. As expected, the seeing was pretty wobbly, but it definitely had its redeeming qualities. Once again, it was mostly medium- to long-wavelength stuff, with a remarkable amount of sharp detail visible amongst the waves. Hard to say how much of this was due to incomplete cool-down, but I think it was mostly just the atmosphere.
If the moon seems like it's getting pretty full, and there won't be much to see, give it a try anyway. Turns out that the western part of the nearside has a bunch of neat features. When it's a couple of days before full like this, think Vallis Schroteri. Think Aristarchus Plateau. Think Gruithuisen domes. Think Gassendi (rilles inside!). Think cool little lakes. Think not just one, but TWO remarkable elongated / double craters right near each other - Hainzel and Schiller. Think Marius Hills! Woo hoo! Turns out that this is a pretty classic part of the lunation.
I didn't take particularly good notes, but as I sit here with my Tupperware of re-nuked pesto spaghetti and a bottle of some friends' homebrew, I'm paging through Rukl to see what stood out...
The first thing that grabbed my attention were two flooded craters: Schickard, right on the terminator, and Mersenius, a bit east of it. Both of these craters were showing an illumination that I consider the creme de la creme of crater lighting: The rim is lit up around the whole circumference of the crater. The western (i.e. sun-facing) inner wall is reflecting brightly. The eastern outer wall (also sun-facing) is already beginning to lose detail, it's so illuminated. There are still shadows at the base of the eastern inner wall. And - this is the good part - the western edge of the floor is still dark - or at least only dimly illuminated. Oh baby. Why do I go so gaga over this? Because it greatly enhances the impression of convexity of the crater floor. Makes it look like a very gentle, yet extremely smooth dome. Shows that the (presumably) flat lava floor is curved, just like the lunar surface. Earth ain't flat, moon ain't flat, ain't none of these things is flat. It's just a lovely effect.
Imagine my surpsise upon turning to map 51 in Rukl and discovering that Mersenius is described as 'Flooded crater with convex floor'. Whoa! Not only am I not the first person to see this, but the Moon Demigod himself describes the floor as 'convex'. Okay, I gotta know. Is it really convex? (More so that just the curvature of the moon's radius, I mean.) Presumably there is stereo imagery from Apollo or Lunar Orbiter, or maybe laser altimetry from Clementine that can settle this. My gut reaction is to be highly skeptical. Presumably that floor is just made of our favorite rock from Gusev - basalt. That lava is runny as heck when it's molten. Just look at pictures of Hawaiian volcanoes erupting. How could it have formed a dome? If it did so, why? Is this a shield volcano inside a crater? That seems highly unlikely, besides, where's the summit crater? Is the crater floor a huge lunar dome, perhaps a laccolith (a blister inflated by magma underground)? That also seems implausible. I've got to go to the literature and find out about this one of these days...
What else stood out? Well, a couple of more lakes. Lacus Excellentiae and Lacus Timoris - Excellence and Fear. Yet another good name combo. At this time of the lunation, it's really fun to look at various points around L.E. and ask 'where does the terra material stop and the patchy mare material begin'? I think that one can actually play this game pretty successfully around L.E. Lacus Timoris is cool, too, I once spent an evening on the back porch, bangin' out targets around there until the cows came home.
The Aristarchus Plateau is nicely lit up, with the famous Vallis Schroteri, King of the Sinuous Rilles, standing out in nice shadowed relief. Didn't really spend a lot of time on it, though, before clouds rolled in and I came inside for this pasta. Caught a quick glimpse of the Gruithiusen Domes. These are located near a promontory of terra / ejecta material at the western edge of Mare Imbrium. Oughta have a name, if you ask me - maybe Promontorium Gruithuisen. Or maybe name it after some famous terrestrial cape, like the Cape of Good Hope, or Cape Horn or something.
Didn't have time to look for the Marius Hills domes, either. Hope that it clears up later. Need to look at Saturn, too.
Posted on sf-bay-tac Tue Feb 3 14:46:34 2004 PT
Converted by report.pm 1.0 Tue Feb 3 22:15:54 2004 PT