The Moon

1998 Mar 3

For once the sky was clear.

Though a bit wobbly, it supported 300x with profit. Observations were done with a C8 at 300x and a 4.5-inch newt at 180x. Contrast was very good. I'll travel around by Rukl Atlas page for the convenience of anyone wanting to "sing along at home."

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The first thing to catch my eye was the Rimae Burg -- all the main tendrils were visible with some patience, particularly the main one running from the mountains through the north of Lacus Mortis (the Lake Of Death! wooo...) past the crater of the same name. One "vertical" stretch near the curious ridge running north of the crater looked very much as if it were made up of a series of small craters. In the right light, all this is a pretty easy target.

The less well-defined craters Mason and Plana offered up the tiny detail inside them (small craters and a central peak in Plana). They are exaggerated by the smoothing caused by partial filling with mare material. Again, the right light is critical to appreciating this.

Rimae Danielli were doing a fan dance. Sometimes I could hardly see the complex, and other times it seemed to sit still in the eyepiece and I'd wonder how it could be difficult at all. The main branching was delicate but definitely visible in full, and there may have been an additional minor branching (but I'm unconvinced). It was almost as inspiring as Triesnecker at its best.

Of course, when in this area, there's Poseidonius. And it was extremely gratifying to get a look at it, since it seems I've been unlucky at this point in every lunation for nearly a year. Against all odds, tonight the whole fat fig was splattered all over my eyepiece with all the rilles and collapses and little craters you could ever ask for. It was particularly well lit to see the subtle height differences in the remaining walls, and at times I was able to see ten significant segments of rille. A really wonderful look at one of the best spots on the moon.

The rilles in Atlas were also easy, and well worth a little time. In poor seeing, it simply looks like a nice, largish crater, but when you can steal a look, you really get a feel for the tremendous tectonic stresses that came into play. Some collapses and minor cratering were also notable in Hercules.

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The Serpentine Ridge (now inaptly named Dorsa Smirnov) was just on "this" side of the terminator, giving it ideal relief. It's easy for any small scope, but amazing no matter what aperture you bring to the party...

If you run along the Dorsa to the south end, you come to Plinius and the terminus of a major rille structure (the rimae Plinius, of course, which extend the Rimae Menelaus... part of a major classic rille structure around the rim of Serenitatis). Three major branches could be easily seen, and they seemed to submarine just below the Serpentine ridge, then reappear slightly beyond a minor dorsa above Dawes.

In the same area is a remarkable dark albedo zone (really an extension of the darkness that edges all of Mare Serenitatis). But this particular spot has exceptional contrast as well as very hard edges; the color change is strikingly sudden.

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For some reason, Romer (Rukl 25) was particularly attention-grabbing tonight, partly because some trick of the light made the edges practically fluorescent, and partly because the central mound and internal crater were very nicely lit for exquisite detail.

Traces of the rimae Littrow were somewhat visible in the early evening, but got more difficult as the night progressed and seeing slowly deteriorated (and the moon moved lower).

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Wandering a bit south of Plinius we arrive at a pair of domes (Arago Alpha and Beta) that were in perfect light; one of the best dome sightings I've had other than Rumker. The mounding seemed exceptionally steep on Alpha, and the central crater was obvious. Beta was considerably more subdued, but also further from the terminator. It's very possible it's also quite a sight when equally well-placed.

Further south in Mare Tranquilitatis is an incredibly complex, nearly radial structure of dorsa centering on a "dorsal ghost" named Lamont. It's an amazing view in this kind of light when both color and shadow contrast are at their best; ridges spider in all directions and as they turn in the light, the play of different patterns is captivating. It's not necessary to point it out or look for it -- the feature will grab you by the throat if you ever get lucky and catch this kind of view.

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I also got one of my best ever views of Rima Jansen (Rukl 36), a delightful little sinuous rille that seems to end in a small crater. There also appeared to be a much smaller rille nearby. The structure is highly reminiscent of the more well known Rima Birt near the straight wall, but the sinuous nature seems more pronounced and squiggly. A nearby tiny section of rille, closer to the naming crater, was fleetingly visible but not commonly charted; you might try looking for it sometime.

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The timing was just right for my observing partner to spot a very pronounced ray in the crater Hypatia (the "heart" of the moon due to its odd shape). The rimae Hypatia were also surprisingly easy, as they have been elusive most of the preceeding year. They run along the edge of the indentation between Serenitatis and Sinus Asperitatis, just north of the crater after which they are named. They peter out into this mare zone with an increasingly narrow fork that's jammed into a small range of hills just off the peninsula. It's tempting to think there is some selenological relationship, but I'll be danged if I know what it is.

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The Altai Scarp (now officially Rupes Altai, which somehow makes me think of "overpriced in Bangladesh") was right on the terminator, in fact a little in shadow at its westernmost. At such a time it shows clearly as the "shock ring" it is -- a rumpling caused by the impact that formed Mare Nectaris. For anyone who has ever hunted down Mare Orientale in a favorable libration at full moon, the resemblance will be obvious save for one thing: on Nectaris, we can get a clear, nearly overhead view of the same effect.

This was actually one of my own first "theoretical" observations (only a hundred years or so too late to be cutting edge...)

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Last on the list for the night was the larger Janssen, a ruined structure in the southern wastelands. Even at first glance, the massive Rimae Janssen were visible in the 4.5-inch. They seem to form a partial inner ring that is filled out by the walls of the larger structure. I have always assumed (without knowing) that this is a slumping ridge where another larger crater collapsed under the present Janssen. Overall, it's one of the easiest massive structures when it comes to seeing the hexagonal shape such massive walled plains often assume. As the lunation goes by, Janssen rapidly disappears, it's ruined walls are so low in our epoch. This is one of those places everyone should visit; the level of detail is such that the most modest to the very best scopes will pay off handsomely.

Dave North; 1998 Mar 4