seven day moon

Newly revealed tonight is the Mare Vaporum, slightly above the midpoint of the terminator and level with class 1 Menelaus which became visible last night. It is roughly the same size as the Mare Crisium, but less well defined. Adjoining it to its south-west is the still smaller Sinus Medii which, as its name might suggest, contains the nominal centre point of the lunar disc from which latitude and longitude are measured.

In the north-eastern part of the Mare Vaporum and due west-south-west of Menelaus is the clearly-defined class 1 Manilius. This is another of the Moon's bright areas, and will develop a minor ray system as the Moon waxes.

To the south-south-east of the Sinus Medii by roughly its diameter is the ring mountain Albategnius. It is an old formation, its walls interrupted by many more recent craters, the most conspicuous of which is class 5 Klein on its south-western edge. In 1962, Albategnius was the target of the first experiment to project a laser beam onto the lunar surface. As is usual for such old, rounded features, its current sharp relief will diminish considerably as full moon approaches.

Due south from here, just short of the southern cusp by about the width of Albategnius, is the foreshortened black oval of the ancient crater Curtius. The inclination of the Moon's axis to the plane of its orbit about the Earth, and the inclination of this plane to that of the Earth around the Sun, give a variation in the maximum altitude of the Sun as seen from the lunar surface of about 12°. At Curtius' latitude of 67° S this gives a maximum altitude of only 35°. It seems likely that parts of the inside near wall are steeper than this, and will therefore not have seen the light of the Sun since the formation of the crater billions of years ago when the Moon was still comparatively young. In such permanent darkness, temperatures will be incredibly low, and it is possible that there may be constituents of the Moon's composition preserved here which could not have survived elsewhere.

Above the Mare Vaporum the eastern end of the enormous Mare Imbrium is revealed - it will take a further three nights to fully emerge from the darkness. Near its middle is the striking class 1 pair of Autolycus, and to its north the slightly larger Aristullus. North-north-west of Aristullus by twice its separation from Autolycus is Piton, an isolated mountain. It can be recognised as such by the illumination of its eastern side, in contrast with the craters. Very few such features exist on the Moon - most lunar mountains belong to ranges such as the Alps which skirt the northern edge of Imbrium. From the Alps, the sharp gash of the Alpine Valley runs north-east across the uplands to the Mare Frigoris to the north. With a powerful instrument, a narrow river-like rille may be seen winding along its floor.