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, during its first quarter. The view crosses Mare Serenitatis (Sea of Serenity) and Mare Tranquillitatis, (Sea of Tranquility), and rightwards to the southern highland region, where the surface is densely covered with overlapping impact craters. 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.