by Marek Cichanski
But the moon was up, and the sky was clear, and there was a bit of a terminator. How could I say no to that? Gotta get in at least 20 minutes or so of observing.
Seeing was wonky, maybe only 2 to 3 out of 5. Only used (600/7)x, whatever that is. I'm too tired to even do arithmetic.
If you haven't looked at Mare Crisium when the sunset terminator is near its eastern edge, give it a try sometime. The contrast between the light, high-standing terra material and the flatter, lower, darker mare material is really amazing, particularly around the south edge of the basin. The highlands crust there has a cracked, lumpy, plateau-y appearance that looks like a thick, cracked, scabbed-up scar. Like serious road rash that's on the way to healing, but which is shedding big chunks of dead skin. Okay, horrible analogy, but true. Like lizard skin, okay?
Another neat thing about this area is that it shows a nice example of a basic sort of geologic relationship that can often be seen at basin edges: An 'embaying' relationship. The most basic sort of relationship that two geologic units can have is an 'overlapping' (aka 'superposed') relationship, where one layer was deposited on top of another. That one's sort of a no-brainer. A slightly more subtle version of the same thing is where one unit laps up against the edge of another unit that has a steep, high-standing edge, but doesn't slosh over that edge. Like water meeting the edge of a bowl. Ocean water conforms to the salients and re-entrants of a coastline, showing that the water came along and filled the ocean basin. Lava often 'embays' the edges of the basin that it fills, as well. The moon has some great embaying relationships, such as at the southern edge of Crisium. In fact, I've heard this 'embaying' principle invoked more on the moon than on the earth.
There were a couple of wrinkle ridges visible in Crisium, too. Dorsum Harker and another one that I'm too tired to look up in Rukl even though it's lying open next to my left elbow. Both were named for geologists. Yeah, baby. Of course, I think that ALL dorsa are named for geologists, now that I think about it... Cool... Harker developed graphs of elemental abundances that are used for classifying igneous rocks. If you got turned on by the purported andesite at the Pathfinder site, and get all tingly looking at the basalt at the Spirit site, you're probably thinking about Harker diagrams, among other things.
Petavius and Langrenus were looking epically awesome. I could gush at great length, but my face is about to hit the keyboard. Magnificent terraced walls. Central peaks for days. Those peaks were casting amazing long shadows. The shadow of the western wall of Langrenus was just about to the central peaks.
It was great to look at the Moon, even if only briefly. Takes away a lot of stress, gives us a nice injection of beauty and contemplation before heading off to beddie-bye...
Posted on sf-bay-tac Apr 07, 2004 00:22:22 PT
Converted by report.pm 1.1 Jul 10, 2004 15:48:57 PT