The lunar terminator. View through a telescope moving across the lunar surface along the terminator, the division between the illuminated and dark parts of the Moon. The view pans across Mare Imbrium (Sea of Rains), with the half-lit Copernicus, 93 kilometres wide, being the most prominent crater. The Moon does not produce its own light, but reflects that of the Sun. As it travels around the Earth during its 27-day orbit, parts of the Moon's surface which are visible from Earth become shadowed by the Moon itself. The Sinus Iridium (Bay of Rainbows), a plain of basaltic lava that forms a northwestern extension to the Mare Imbrium, is visible at the end of the clip.