day moon
The gibbous Moon will be visible for most of night, and will transit during the hour before midnight. An observation might reasonably span midnight, starting on one day and finishing on the next (hence the two-day heading for this page). Apart from the features described here, a separate Tour of Bright Objects covers features which become prominent across the whole lunar disc around the time of the full Moon.

The Moon is now very close to full. Unless there is due to be an umbral lunar eclipse, the Moon will be passing slightly above or below the Earth's cone of shadow. The terminator will not disappear from the western limb and reappear on the eastern one, but will "roll" from west to east via either the north or south pole. This rolling effect may be noticeable tonight and, coupled with libration, may affect the apparent position and even the visibility of some features. Details of eclipse times and locations can be found in the Inconstant Moon Diary.

The most conspicuous feature to be revealed tonight is a dark oval near the north-western extremity of the Moon's bright southern region and just below the Oceanus Procellarum which occupies much of the western edge of the lunar disc. This is class 5 Grimaldi - its floor is one of the darkest parts of the Moon's surface with an albedo of 0.06.

Byrgius Roughly two Crisium widths to the south, level with the small, oval Mare Humorum lies Byrgius. It is an old class 3 crater, but has been splashed with bright ejecta by the young Byrgius A which interrupts its north-eastern wall, making it a bright object even by the standards of the southern hemisphere. Another two Crisium widths south along the edge of the lunar disc is the neatly defined oval of class 2 Inghirami.

Close to the terminator, about one Crisium length north from the northern "shore" of the Oceanus Procellarum, stands large class 1 Pythagoras, with its fine central peak. Only its position near the limb prevents it from being one of the most impressive features visible. By contrast look one Crisium length north of Grimaldi, on the edge of Procellarum Luna 9 (roughly the spot where the Soviet probe Luna 9 made the first soft landing in 1966), then one Grimaldi length due east from here to the small bright spot of Reiner. To the north-west of here, again by one Grimaldi length, is the tiny light speck of Galilaei (Galileo). It is probably the least impressive feature included in Inconstant Moon, and is hardly a fitting tribute to one of the most influential figures in the history of science, and the first man to point a telescope at the Moon and see it for what it is: a mountainous, three-dimensional world.