Around its sunrise and sunset, when it is illuminated from a low angle, this huge walled plain - seen here relative to Tycho, can even be seen with the naked eye. However, when the Sun is overhead and the Moon is near full, despite being 16,000' deep, it becomes invisible to even the most powerful telescopes.

Photo: Morio Higashida. The full size original of this and other photographic and CCD images may be seen on his Invitation to the Moon site.

Inconstant Moon