19 June 2014
The Short Answer (TSA)
Lunar Eclipse
The word eclipse comes from an
ancient Greek word meaning "the darkening of a heavenly body." For there to be a lunar eclipse, two things
must happen. First, the Earth must move
in between the Sun and the Moon. Second,
the Moon must move exactly into the shadow cast by the Earth.
Lunar Eclipse Diagram
Lunar eclipses don’t happen that
often, but why not? The Earth moves in between the Sun and Moon every month. In fact, the Full Moon is the exact moment when the earth is in between the Sun and the Moon. But only rarely is there a lunar eclipse with the full moon.
There are two reasons. First, the Earth casts a very small shadow
and the Moon is a very small target.
Second, the orbit of the Earth around the Sun and the Moon’s own orbit
around the Earth are not all on exactly a level plane. So, most often, the Earth is a bit above or
below the “level” of the Sun -- and/or -- the Moon is a bit above or below the
level of the Sun and Earth.
Again, the Earth casts such a small
shadow and the Moon is such a small target. During most Full Moons, the shadow of the Earth will “miss” and pass
just above or below the Moon. So, most
often, all we see is the full sunlit face of the Moon.
But, once in a while, the Earth, and
Moon will line up on exactly the same level plane. When that happens, a sky watcher will see a
Lunar Eclipse. The Full Moon is suddenly darkens as a shadow moves across the face of the Moon until the whole Moon
is completely covered by a dark shadow.
But if you look carefully, you’ll
notice that you can still see the faint outline of the darkened Moon. It has a very dark reddish color. From beginning to end, a Lunar Eclipse will last about 1 hour and 45
minutes.
Video: Lunar Eclipse -- Described and Illustrated
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