| Lunar Eclipses When the Moon is situated directly opposite
the Sun and Earth and crosses the ecliptic at a given time, a lunar eclipse occurs. When
such an alignment takes place, the full Moon passes through Earth’s shadow and its
apparent brightness is greatly subdued. But it is never completely blackened from view as
one might imagine. Due to refraction, sunlight passing through Earth’s atmosphere
results in a small amount of light reaching the Moon giving it a deep reddish appearance
in the case of a total lunar eclipse.
The outer part of Earth’s shadow is called the penumbra, while the much
darker central region is referred to as the umbra. A total eclipse only occurs when
the Moon passes completely through umbra.
A partial eclipse occurs when the Moon only passes through a portion of the
umbra. A penumbral eclipse occurs when it only passes through the less dark
penumbra. The darkening effect of the full Moon during a penumbral eclipse is far less
obvious.
Extract from
Atlas of the
Southern Night Sky
Massey - Quirk
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