Fourteen Day Old Moon (Full Moon)

Full Moon is, in general, the worst possible phase to observe; the sunlight is striking the surface from behind us, it is high noon on the Moon, and shadows are at a minimum, just as with noontime on the Earth.

Occasionally, however, all direct sunlight is cut off. This happens when the Moon moves into the shadow of the Earth. The primary shadow, known as the umbra, is darkest. This merges into the penumbra, where the Sun is progressively less and less obscured, due to the Earth's atmosphere and diffraction effects. In this area an observer standing on the Moon would see a partial solar eclipse occur. For more details, see the section on eclipses.


Key Features to Observe Tonight

Near Full the brightest feature of all becomes quite prominent: this is the crater Aristarchus, in the Oceanus Procellarum. All the uplands on the Moon are overlaid with a gray deposit, which presumably is meteoric ash, but the coating on Aristarchus is certainly unusual. It is one of the features which often show up distinctly under Earthshine conditions.

Remarkable contrast is afforded by the nearby Grimaldi, a colossal crater, but so near the limb that we get only a very oblique view of its floor. This floor is of a dark steel-gray hue, even darker than that of Plato, and with the exception of one or two isolated spots it is the darkest surface on the Moon. Like the Mare Crisium, Grimaldi is a good guide for libration conditions.


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