Hitchhiker's Guide to Rukl Chart 59

Petavius (...Akkana)

Petavius, when lit from behind (just past full moon), has an interesting ring around its southwestern edge. It's too close to the main crater to be a typical shock ring; perhaps a wall slump?

Petavius (JRF <freeman _at_ netcom.com>)

Petavius is a "landmark" feature, easily recognized and useful for orientation. This great crater is crossed by several rilles, of which the first -- Rima Petavius I -- is especially prominent. If you are set up for deep-sky observing on a night not long after the new Moon, do have a look at Petavius before the Moon sets.

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

Petavius is downright famous for its incredible radial rille, jutting out from the central peak, and visible in even bad seeing. What is not often glimpsed is the rest of the rille structure that makes the interior Rimae (rather than rima) Petavius. There are two more major secions, one more or less radial in nature, and the other more of a rough crosshatch, that can be very difficult to spot. The third rille is normally a very hard target indeed (seeing limited).

See also Gang of Four.

Petavius (Steve Coe <scoeandlross _at_ sprintmail.com>)

There are 4 central peaks in a cluster, this is a big old crater with smooth, slumped walls, there are 3 craterlets in a straight line near the central peak. Also a most unusual feature: a dark, straight line in Position Angle 120 degrees from the central peak to the rim of the crater--like drawing a radius of a circle in geometry class.

Vallis Snellius (Matt Tarlach <tarlach _at_ earthlink.net>)

From Petavius I turned my eye west, toward the terminator, and things got really interesting. Vallis Snellius could be traced over at least 70 km of the lunar surface, from a small, well defined crater about 30 km west of the crater Snellius westward, to a somewhat dark area southeast of Borda. A notch like shadow just south of Borda lines up perfectly with the rest of Vallis Snellius, suggesting that the valley may continue at least that far west. (The dark area near Borda is interesting in itself, as in addition to its tone it appears smoother and lower than the surrounding rugged craterlands. Perhaps it is the flooded floor of an ancient crater, the walls of which have been totally destroyed by later impacts?)

The appearance of Vallis Snellius is quite different from the more famous Alpine Valley. At first I took it for a crater chain, as it appears broken and segmented yet with all the dark areas laid out in a perfectly straight line. On closer inspection the valley looks like an area where the lunar crust has subsided, apparently after many of the craters atop it had been formed. The slumping crater walls create the broken and chain-like appearance.