Hitchhiker's Guide to Rukl Chart 26
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
- 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
- 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
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
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.
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...)
This page last modified: Dec 06, 2020
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