Definition of: eclipse

(i·klips′) noun
1. Astron. The dimming or elimination of light reaching an observer from a heavenly body. A lunar eclipse is caused by the passage of the moon through the earth's shadow; a solar eclipse by the passage of the moon between the sun and the observer.
2. Any hiding or obscuring. See ANNULAR ECLIPSE.
—v.t. e·clipsed, e·clips·ing
1. To cause an eclipse of; darken.
2. To obscure the beauty, fame, worth, etc., of; overshadow. [<OF <L eclipsis <Gk. ekleipsis <ek- out + leipein leave]
ECLIPSE
S. Sun. E. Earth. M. Moon. EO. Earth's orbit. MO. Moon's orbit.

When the moon passes between the sun and the earth, it causes an eclipse of the sun, this solar eclipse being total to observers within the umbra (darker shaded portions) of the moon's shadow and partial to those within the penumbra (lighter portions). When the moon passes through the earth's shadow, earth observers witness a total or partial lunar eclipse.