Hitchhiker's Guide to Rukl Chart 26

Cleomedes (JRF <freeman _at_ netcom.com>)
This prominent crater has rilles on the floor. It would be a noteworthy landmark feature, except that with Mare Crisium right next door, who needs it.
Mare Crisium (JRF <freeman _at_ netcom.com>)
Bystanders may be amused to note that the Sea of Crises resembles the face of a teddy bear, or perhaps a hedgehog. (Which may depend on libration.) Craters Peirce and Picard are the eyes, the snout is between Promentory Olivium and Promentory Lavinium, and broad embayments at the north and southeast borders of the sea form the ears. There are many wrinkle ridges on the floor of Mare Crisium, visible under grazing illumination.
Mare Crisium (David North <d _at_ timocharis.com>)
Crisium is persistently granular when lit "from the other side" (near the terminator after full moon). I have no idea why this should be so.
Mare Crisium (Bill Arnett)
On a silly note, the whole of Mare Crisium looked tonight just like a baby seal about to pounce on Palus Somni: the two eastern dorsa are the ring around its neck, the two prominent craters (Pierce & Picard?) are the eyes, the little dorsa just west of there are whiskers. :-)
O'Neill's Bridge (...Akkana)
The January '98 issue of Sky & Telescope magazine described a feature in western Mare Crisium first noted by John O'Neill in 1953. O'Neill believed he was seeing an artificial "bridge" on the moon.

The "bridge" extends from Promontorium Lavinium to Promontorium Olivium, and is visible at sunset but not at sunrise; try for it about four nights after full moon. The easiest way to find it is from Proclus, the prominent crater near the eastern point of diamond-shaped Palus Somni (which stands out as a dark highland area adjacent to Sinus Amoris).

On 6/11-12/98, I observed the area of Promontorium Lavinium and Promontorium Olivium with a VX102 varying from 111x to 263x. This is a feature which will probably require high magnification to see; I couldn't make out much detail at 111x, and the area was much clearer at 200x and 263x despite having to wait for instants of steady air where the image would briefly sharpen enough to discern any detail.

Even so, the connection between the two promentories did not look like a bridge to me; perhaps like a dam, with buttressed walls. But the area of bridge was still half a day away from sunset, so perhaps I was too early. I'll try again next month.

On November 14, 2000, 1:17am & 1:45am PST Bill Arnett caught several images of the O'Neil's Bridge area in nearly perfect light.

Promontoria Lavinium and Olivium (Randy Muller <71172.1234 _at_ compuserve.com>)
The 'delta' formed by Promontoria Lavinium and Olivium and the crater 'E' (Peirce E? Picard E? Yerkes E?), Yerkes and a ridge joining Yerkes and E was well lit and well distinguished from the rest of the floor of Mare Crisium by the shadow of the two craters and the ridge between them.

This area looks much different (and better) under these lighting conditions than the representation in Rukl's atlas.

It was early morning in this area, but the article was about the appearance of this area at sunset. There is no illusion of a bridge under these conditions.

Yerkes (...Akkana)
In evening light, the west wall of the ghost crater Yerkes looks like an extension of the wrinkle ridge running from Yerkes to Yerkes E (or is it Proclus E? I share Randy Muller's confusion there) until the seeing steadies enough that the less prominent eastern wall of Yerkes fades into view.

In morning light, all of Yerkes is much more apparent, as is its more ghostly neighbor to the south, Lick.

Palus Somni (Randy Muller <71172.1234 _at_ compuserve.com>)
Palus Somni is a curious cross between lunar maria and lunar highlands. It is intermediate brightness, and appears to extend as a a fan-shaped spray of debris from Proclus, but it is not normal ray material. There are significant rays from Proclus, but they extend everywhere, except in the direction of Palus Somni.
Palus Somni (Jane Houston <jane _at_ whiteoaks.com>)
Palus Somni -- the Marsh of Sleep -- was a light grey ovalish region in between the darker Mare Crisium and Mare Tranquillitatus. It looked like a land mass surrounded by black sea. It loooked like an island - a raised area, to me. The two craters Macrobuis and Tisserand (RUKL 26) were especially striking tonight.
Proclus (David North <d _at_ timocharis.com>)
The best I've seen are guesses [for why the rim of Proclus is so much brighter than surrounding features]. Dinsmore Alter states: "...the second brightest feature of the moon makes its appearance just off the right hand shore (of Mare Crisium) attracting almost as much attention as the mare itself. This is the extremely bright explosive crater Proclus. Craters of this kind, which have resulted from unusually violent explosion, brighten under a high sun much more than do the surrounding areas."

The problem is, other readings differ with Alter. There seems to be some consensus that the brightness is caused by a combination of underlying materials being thrown up, and possibly some alteration they undergo in the high temperatures of impact -- but it may just be that the impact took place where a deposit of unusually light colored material was waiting.

There is further conjecture that the exceptional brightness of some craters is due primarily to the youth of the crater, and that there is little variation in the brightness of the ejecta in major regions of the moon. It's worth noting that the number one bright feature, Aristarchus, is almost half way across the moon but located at the edge of a plateau and mare material, which is not unlike Proclus.

They both have rays, but Proclus has the more spectacular, and strangest. There is a large gap in the system in the direction of (or defining) Palus Somni.

Another young crater, Tycho, has a similar gap in the direction of mares Nectaris and Fecunditatis, with the exception of a single large ray that bisects them (roughly).

So: it's not entirely clear why the crater is so bright, but there's some info that might help you think about it and draw your own conclusions. Palus Somni and Proclus are a truly odd feature; Alter thinks the marsh subsided subsequent to the impact, and that makes sense, but why "sinking" would make it darker is unclear, unless this were from some baking process (or other factor I'm not up on; Alter often does not explain himself...)

Moon-Lite Atlas for chart 26

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