Four Day Old Moon‡

The best time to observe the Waxing Crescent Moon is in early evening, during the early hours of darkness, before it sets in the western sky. The Moon appears to be chasing the Sun, but cannot keep up; it rises about an hour later each night. For the next two weeks or so, that will work to our advantage. The Moon sets a few hours after sunset (transit occurred during daylight hours).


Key Features to Observe Tonight

The contrast between Mare Crisium and its bright surrounding uplands is more pronounced tonight, and will continue to increase on subsequent nights. On the western side of Crisium is a bright spot, which is Proclus. This area will continue to brighten still further in the coming nights.

South of Mare Crisium and mostly lying below the lunar equator, Mare Fecunditatis is seen fully illuminated now. Midway between them, the eastern end of the Mare Tranquillitatis is also revealed, with its smaller companion Sinus Concordiae to the east. Mare Spumans is the name of the small sea east of Concordiae, which looks quite crater-like for being named as a sea.

In the northern part of Mare Fecunditatis, where it meets Mare Tranquillitatis, is the crater Taruntius, its bright crater rim rising from the dark lava floor. The crater Cauchy appears as a small, sharp circle in Tranquillitatis. It lies between a pair of diagonal lines, which are adjoining rilles or clefts. The northern is named Rimae Cauchy, and the southern one is Rupes Cauchy. Rupes Cauchy is a southwest-facing fault which appears dark at this time of the lunar cycle but it will change to appear as a bright line in about two weeks, under the setting sun illumination.

At the southern border of Mare Fecunditatis, near the terminator, lies the eastern portion of the Mare Nectaris, which will appear more completely tomorrow. Between the two maria, is the broken ring crater Gutenberg, a very unusually shaped formation. Immediately southeast of it is the crater Goclenius. The Pyrenees Mountains, west of the crater Columbo, form the eastern border of Nectaris and run south, almost to the crater Santbech.

Further south in the cusp area is an interesting cluster of craters. Two of them, Metius and Fabricius, form a figure 8. Fabricius is actually inside the warn and old looking walled plain Janssen. Northeast of them is Vallis Rheita (Rheita Valley). This long fault is never very easy to observe because of its location near the limb and rugged surroundings, but is usually best seen on this night.


‡with permission from Lunar Discoverer User's Manual by Robert Duvall, 2013