The obscuring of one celestial body by another.

(1) A Solar Eclipse occurs when the Moon comes between the Earth and the Sun. In a total eclipse, the solar disk is completely obscured; in a partial eclipse the solar disk is only partly obscured. An annular eclipse occurs when the Moon is near its apogee and the apparent diameter of the Moon is less than that of the Sun so that the Sun is never completely obscured. "First and last contacts" are defined as the times of tangency of the solar and lunar disks. A central eclipse (which can be total or annular) has two additional times of tangency: "second contact," when maximum eclipse begins, and "third contact," when it ends. The last glimpses of the Sun through the lunar valleys, just before second contact, are known as Baily's beads.

(2) A lunar eclipse occurs when the Moon enters the shadow cast by the Earth.

(3) Spacecraft in the Earth's shadow are said to be in eclipse.