A lunar eclipse occurs when the
Moon moves into the Earth's shadow. This can occur only when the Sun, Earth,
and Moon are exactly or very closely aligned with Earth between the other two,
and only on the night of a full moon. The type and length of a lunar eclipse
depend on the Moon's proximity to either node of its orbit.
A totally eclipsed Moon is
sometimes called a blood moon due to its reddish color, which is caused by
Earth completely blocking direct sunlight from reaching the Moon. The only
light reflected from the lunar surface has been refracted by Earth's
atmosphere.
Earth's shadow can be divided into
two distinctive parts: the umbra and penumbra.
A penumbral lunar eclipse occurs
when the Moon passes through Earth's penumbra. A special type of penumbral
eclipse is a total penumbral lunar eclipse, during which the Moon lies
exclusively within Earth's penumbra.
A partial lunar eclipse occurs when only a portion of the Moon enters Earth's umbra, while a total lunar eclipse occurs when the entire Moon enters the planet's umbra.