Thirteen Day Old Moon‡

The Moon is now very close to Full, rising near sunset and setting near dawn. It transits around mid-night, which makes observing ideal, as you view through the least atmosphere in dark skies without requiring a late night of observing. Unless a lunar eclipse expected, the Moon passes slightly above or below the Earth's orbital plane and shadow. A lunar eclipse occurs when the shadow from the Earth falls onto the Full Moon's surface.

The terminator does not just disappear from the western limb and reappear on the eastern one, but appears "roll" or "rock" from west to east by pivoting about the north or south pole. This rolling effect may be noticeable tonight and, as with libration effects, will affect the apparent position and visibility of features near the limb.


Key Features to Observe Tonight

Pythagoras, far to the north near the limb, with its fine central mountains is a fine sight when librations allow. Foreshortening interferes with observations of this impressive feature.

The most conspicuous feature to be revealed tonight is the very large, dark oval crater named Grimaldi. Its floor is one of the darkest parts of the Moon's surface. It lies just below the lunar equator, close to the western limb, in the Moon's bright region just southwest of the huge Oceanus Procellarum which occupies much of the western edge of the lunar disc.

West of Mare Humorum lies the small oval shaped Byrgius. It is an older crater, splashed with bright ejecta by the younger Byrgius A which impacted on its northeastern rim. Further south near the limb is the neatly defined oval of Inghirami.

West of Kepler, roughly half way to the limb, lies is another bright spot: the small crater Reiner and its bright mark Reiner Gamma. Northwest is the small crater named Galileo. It is not at all impressive, and is hardly a fitting tribute the first man to point a telescope at the Moon.


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