This image explains how the Earth's shadow causes a lunar eclipse. Notice the difference between the umbra and the penumbra.
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Lunar Eclipses
Lunar eclipses are special events that only occur when certain conditions are met. First of all, the Moon must be in full phase. Secondly, the Sun, Earth and Moon must be in a perfectly straight line. If both of these are met, then the Earth's shadow can block the Sun's light from hitting the Moon.
There are three types of lunar eclipses. Which one we will see depends on the alignment of the three celestial objects. But first, you need to know that the Earth's shadow is broken up into two parts. The umbra is the darker part of the shadow, where no part of the Sun can been seen. The penumbra is lighter than the umbra, because part of the Sun can be seen.
So, when part of the Moon passes through the umbra, this is called a partial eclipse. When all of the Moon passes through the umbra, this is called a total eclipse. Finally, when the Moon only passes through the penumbra, this is called a penumbral eclipse.
Now that you know all about eclipses, you can step outside and enjoy the show! Remember that lunar eclipses are not dangerous to the eye, so you don't need protection to watch. Just find a nice, cozy spot and enjoy!
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