fifteen-sixteen day moon

The Moon is now just past full. Unless there is was an umbral lunar eclipse, the Moon will have passed slightly above or below the Earth's cone of shadow. The terminator will not have disappeared from the western limb and reappeared on the eastern one, but will have "rolled" from west to east via either the north or south pole. This rolling effect may still 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.

With favourable libration, running southwards from the midpoint of the western limb (adjacent to the dark oval of class 5 Grimaldi) some slight irregularities may be seen in the otherwise smooth edge of the lunar disc. These are the Cordillera Mountains, some peaks of which rise to over 20000'. They are part of the rugged outer ring surrounding the curiously named Mare Orientale (Eastern Sea), a gigantic far-side feature which may be glimpsed under extreme libration.

Across on the eastern side of the disc, northwards from the Mare Crisium by about twice its length is the distinctive dark ellipse of class 5 Endymion, similar in appearance to Grimaldi. Next to the terminator adjacent to Endymion lies another, dark area - this is the Mare Humboldtianum, the Humboldt Sea.

Following the disc's edge, roughly ²/₃ of the way down to the Mare Crisium, the large walled plain Gauss is seen in the strong relief of the lunar sunset. Further along the terminator, 2¹/₂ Crisium lengths south of Crisium itself, lies another walled plain - the large class 2 Humboldt, curiously some 1500 miles from its namesake Mare. Tonight is the last chance to see this, the first feature described in Inconstant Moon after the new moon.

Another Crisium length further south is the small, dark, class 5 Oken. It appears as the northernmost and best defined of a cluster of flooded patches, collectively dubbed the Mare Australe.