Hitchhiker's Guide to Rukl Chart 24

Rimae Plinius / Serpentine Ridge (...Akkana)

When just on the terminator, there's a broad dark stripe near Rimae Plinius which gives the illusion of being a gradual step-down from Plinius to the Serpentine Ridge. The dark streak (which Rukl shows as an albedo feature) leads into a dark patch the terrae adjacent to Mare Nectaris. Adjacent to the dark patch is a bright white area around the small crater Clerke.
Under some lighting conditions, Rimae Plinius split the south end of the Serpentine Ridge like the cracks across the Mid-Atlantic Ridge here on earth.

Rimae Plinius (David North <d _at_ timocharis.com>)

Near Plinius, I saw something of a bright cross that trailed off to the south -- not a feature I remembered, and standing out as if it were painted there. I did recall there was a rille just north of Plinius, but this entire structure seemed more west than north.

Off to the charts. Sure enough, Rukl shows Rima Plinius just north of the crater, with one main trunk and two parallel lesser rimae (I only saw one line no matter how hard I looked).

Nothing running in a north/south direction at all, save for an indistinct dorsum that should have shown some breakage (but part of it was roughly in the right place. The rille was marked in the wrong place, but maybe close enough). Hmm.

Times Atlas comes out. Again, same features shown, just a bit more detail.

Logically, it would somehow be the main rima crossed by the wrinkle ridge, but it was close enough to the terminator that I would expect the ridge to show as they normally do, and the rille would be more dark than light.

I can't convince myself that what I saw was what is charted, as both my eyepiece impression and the crude sketch I made show it in utterly the wrong place.

I'm pretty sure it wasn't a lunar "crop cross," though.

Rimae Plinius (Bill O'Connell

I have a recent video capture that just barely shows the cross Dave is speaking of, taken under similar lighting. conditions. This image doesn't solve the mystery. The "upright" is clearly the dorsa shown on the maps; the fainter "crosspiece" isn't one of the mapped rilles. Could it be just a contrast feature?

Rimae Menelaus (David North <d _at_ timocharis.com>)

In a southern nook of Mare Serenitatus, I spotted a fine rille structure that did not look familiar; it turned out to be Rimae Menelaus, which I have previously found difficult. Paradoxically, rimae Plinius made no impression at all this evening. Shifting light...

Serpentine Ridge (David North <d _at_ timocharis.com>)

The Serpentine Ridge (accidentally misnamed Dorsa Smirnov, but forget that crap), right on the terminator, is ideally placed to appreciate how complex and rugged this structure is.

Dorsa Smirnov (Brent Hutto <BHutto _at_ InfoAve.Net>)

I have a foldout Moon map (it's a "Hallwag") and the N end of the ridge appears on the map to have a bit of space separating it from the W wall of Posidonius. To my eye through the telescope, it seems as though the ridge merges into the crater rim. OTOH, I could clearly see the very dark material coming down from Posidonius between the ridge and Le Monnier.

Question: 2/3 of the way toward the south of the ridge, when it makes that pronounced S-bend, is the ridge not as tall from there south or is it that the S-bend makes the ridge more parallel to the sunlight and therefore there's just not as much shadow? It appears to me that the S-bend is a saddle point in the ridge.

Serpentine Ridge (...Akkana)

In reply to Brent's comment: Rukl shows the ridge as being almost nonexistant in the S-bend: there are two disconnected mountain chains with a break in them at about 23 degrees north from about 24 to 25 degrees east, with a few smaller north-south oriented hills between the two chains, exactly like what you would see on the earth if a fault line altered the course of a mountain. (The southern ridge is apparently Dorsa Lister rather than Smirnov.) I wonder if similar forces on the moon could have caused this jog in the mountain chain?

On 4/14/98 at a little after midnight, sunset in Mare Serenitatis, right next to the Serpentine Ridge on the terminator the lit walls of dark Posidonius showed as a half-circle of light looping out from the bright part of the moon.

Dorsa Aldrovandi: The Moon Mouse (...Akkana)

8/16-17/2003: The Moon Mouse! Near the Serpentine Ridge, Dorsa Aldrovandi sources from a small mountain that, under the proper lighting conditions, looks like a mouse, with the wrinkle ridge its long tail extending out across Mare Serenitatis.

Bessel (David North <d _at_ timocharis.com>)

Bessel is basically grand central station, and in the right light this effect becomes striking. Three branches of dorsa converge on it, but none of them are particularly notable (I'm unclear of their names; they seem to be extensions of Dorsa Lister in the southeast, Dorsa Buckland to the west, and Dorsum Azara to the north. But none of the branches of which Bessel is the hub are designated specifically.

The light was so oblique that the north/south portions seemed almost like rilles, but they could be distinguished as dorsa fairly easily because they were (a) quite wide and obvious, and (b) I'm convinced if there were a rille that choice I'd know it by now!