nine day moon

Tonight the westward movement of the terminator has revealed one of the Moon's finest sights: the magnificent class 1 ring mountain Copernicus. It is not the largest (this title belongs to Bailly) or deepest (probably Newton), or the brightest (its albedo being 0.16) nor does it have the largest ray system (Tycho). Its prominence is due to a combination of these factors and its fine position in a smooth Mare just north of the lunar equator.

To the north, the Carpathian Mountains ring the southern edge of the Mare Imbrium, and beyond them, one Crisium width away from Copernicus, the small class 1 Pytheas stands out well against its smooth, dark surroundings. Continuing further still, the distinctive, deep dark circle of class 5 Plato marks the northern shore of Imbrium. Scattered across the area to its south are the peaks of the Teneriffe Mountains. They appear to be the tallest summits of a denser range, now largely submerged beneath the smooth surface of the Mare. Beyond the uplands to the north of the Mare Imbrium, the long, narrow Mare Frigoris continues to be revealed.

South-south-west of Copernicus by a couple of lengths, class 1 Reinhold is small but clear. Another two Crisium widths further south, the slightly larger class 1 crater Bullialdus, with its large central peak, is conspicuous in the middle of the western edge of the dark Mare Nubium. To the south-east by about the same distance again, Tycho, class 1 again with a distinctive central peak, is a little larger still, and brighter already than last night when it first became visible.

One Crisium width to the south of Tycho is the huge class 2 walled plain Clavius, the second largest nearside crater. Even foreshortened it is a dramatic sight, and careful observation reveals that its floor is convex due to the Moon's surface curvature. Across this floor, a series of diminishing craters runs in a pleasing arc from the south to the west wall. There are six in all - it is an interesting test of an instrument's resolving power to count how many are visible.