Hitchhiker's Guide to Rukl Chart 52

Robin Casady's CCD image of Mare Humorum, including Rimae Mersenius and Rupes Liebig.

Mare Humorum (JRF <freeman _at_ netcom.com>)

The Sea of Moisture appears very dark at high sun angle, and is prominent in a naked-eye view of the full Moon.

Mare Humorum area (Akkana)

The area around Mare Humorum is particularly rich when near the terminator. Hippalus stands out as an incomplete "ghost crater". To the south, Doppelmayer and nearby Puiseux are other interesting "ghost craters". On the western edge of Mare Humorum, Rimae Mersenius and Rupes Liebig (really on chart 51) stand out prominently.

Gassendi on the terminator (Akkana)

When Gassendi is right on the terminator, its southern wall stays dark much longer than the rest of its walls, making it obvious how that side of the crater has sunk along with the mare it borders.

Gassendi (JRF <freeman _at_ netcom.com>)

Prominent ringed plain with a rille system on its floor. Gassendi is a "landmark" feature, easily recognized and useful for orientation. Look for II and VII, near the east wall.

A close-up of Gassendi, by the Lunar Prospector spacecraft, was the Astronomy Picture of the Day for 2/12/99.

Mersenius area (JRF <freeman _at_ netcom.com>)

To the southwest of Gassendi, Rupes Liebig and its extension, Mersenius rille II, traced a north-south chord across the mare as far south as Mersenius G. Mersenius II was less distinct, but I could trace Mersenius I all the way from just north of Mersenius D to about 16 degrees south latitude. I could not see the complete de Gasparis rille system, just I and III. This area would be worth looking at with greater aperture in favorable conditions.

Lobster/Trilobite (Akkana)

On the far northern edge of Mare Humorum, just northeast of Gassendi, is an interesting structure standing out in relief against the smooth plain of the mare. It looks like a trilobite, or perhaps a lobster. The structure is shown well at the very top of Rukl chart 52, at 37 degrees west latitude.

Doppelmayer (Robin Casady)

Mare Humorum was a particularly interesting area. Doppelmayer showed a large central peak and--unlike Rukl's drawing--looked to have a broken concentric ring around the peak. Rukl shows detail to one side of the peak. The view last night gave the appearance of a broken ring all the way around. Rimae Doppelmayer was clearly in evidence. Some of Gassendi's rilles were easily seen, but I was distracted by Doppelmayer, and didn't spend much time on it.