Moon, 4/6/2009

Marek Cichanski

Moon, home, M603

I've got the laptop set up on a little camping table next to the scope. Not a bad way to achieve `digital capture' of my Moon OR, I think.

Full-disc view with 24mm Panoptics in Denk II binoviewer:

The Moon is a classic waxing gibbous tonight, about halfway between First Quarter and Full Moon. It's interesting to look at the position of the terminator at different latitudes:

On Rukl 02 and 03: The terminator appears to pass along the western edges of Harpalus (45W), John Herschel (47W) and Anaximenes (50W).

On Rukl 09: Western edge of Mairan (44W).

On Rukl 18: Center of Aristarchus (47.5W). The Montes Harbinger are shown to great effect, with brightly illuminated sun-facing slopes.

On Rukl 29: Just west of Kepler C (43W).

On Rukl 52: Western edges of Gassendi and Doppelmayr (42W).

On Rukl 71: Northwestern tip of Schiller (42.5W).

Although the data are a bit `noisy', one could argue that the terminator is not perfectly north-south. It appears to be a bit farther west at the more northerly latitudes, and a bit farther east at the more southerly latitudes. For the purposes of illustration, we could exaggerate the tilt a bit and say that it runs from NW to SE. This suggests that, as seen from the near side of the Moon right now, the Sun is south of the celestial equator.

That doesn't make a ton of sense, unless I'm missing something, because the Moon is near Regulus, and we're just past the spring equinox, so everything ought to be lined up fairly well E-W. I suspect that we're seeing the effect of the Moon's libration. It's probably the Moon that's tilted, not the terminator. Speaking of libration, the eastern limb seems to be fairly well tilted towards us, because I can see Mare Marginis and Mare Smythii quite nicely. Chuck Wood's ``Lacus Risus Felis'' is plainly visible.

I'm working with Rukl's Libration Zone 3 map. The view of this region is very nice, despite the lack of shadows. That high sun angle, though, makes it hard to identify features. I can see all the way around Mare Smythii, to the mountains beyond, which are nicely silhouetted against the blackness of space. There's a prominent lava-floored crater with a bright central peak complex between Marginis and Smithyii. I suspect that it's Neper. I can also see a flooded crater to the northwest of Marginis, this could be Hubble.

Farther south, Mare Australe can be seen. Some dark, lava-floored craters can be seen between Smithyii and Australe, but Rukl doesn't show anything particularly dark in this area that would match them, at least not on the libration charts.

What else do we see in the full-disc view? Tycho and Clavius are prominent, although probably less so than they were a night or two ago. There is still some nice illumination on the craterlets in Clavius. Schiller is quite dramatic, with its floor still in shadow. Although Zucchius isn't visible yet, the twin shock rings of the Schiller-Zucchius basin can be seen extending SE from Schiller, if one knows where to look. It's a neat way to see that basin, as it just begins to emerge into the light. Hainzel is quite dramatic, too; it's always nice to see Hainzel and Zucchius both illuminated like this.

Mare Humorum and Gassendi are very prominent tonight, with Gassendi and all of its complexities being a real star of tonight's show. Farther to the north, across the plains of the Oceanus Procellarum, Aristarchus and the Montes Harbinger are putting on quite a display. Northward again, the Gruithuisen domes stand out prominently, teasing the observer with the ever-elusive prospect of seeing the 900m-diameter crater atop Gruithuisen Gamma. The Sinus Iridum is still nicely lit, with the Promontorium Lapace still casting a bit of a shadow. The rough, jumbled terrain of Imbrium's northwest rim, around the Sinus Iridum, is very nicely seen. I guess that technically, this constitutes the Montes Jura.

A short hop to the north across Mare Frigoris, and we've arrived at John Herschel, completing our tour around the `rim' of the illuminated Moon.

21:10: The seeing is getting pretty good, 3.5-4 out of 5, as opposed to 2.5-3 that I had before. I think I'll go for the 9mm Naglers now.

The Rimae Gassendi are showing up quite nicely, including two that appear to cut the northwest rim.

I've been following Wood's story about the Humorum area, which I always enjoy. I've looked pretty hard for Rima Herigonius, but I can't quite say that I've seen it. I did, however, shoot on up north to the Gruithuisen domes, and I feel like I've gotten about as good of a `view' of the summit crater on Gamma as ever. It's still not the sort of sighting that makes me want to leap up at shout ``There it is! Fast as a goose!'', but I still feel about 75% sure that I saw it. It's beginning to occur to me that tough, small targets are like boundaries that we almost never cross at a steep angle, but rather slide up to asymptotically.

21:46: Okay, now I'm getting closer to shouting ``fat as a goose''. I really think I'm seeing the crater. The mountain with the crater in it is starting to look like Wiley Post's old pressure suit helmet with its round viewport.

Overall, a decent little night with the Moon.

-Marek