Eclipse of the Moon

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About twice a year, the moon becomes orange for several hours. You can easily observe this phenomenon with the naked eye or with binoculars or a small telescope. What is going on ?

This is an eclipse of the Moon. Sometimes, when it is the full moon and our satellite is perfectly aligned in the Earth-Sun axis, the Moon comes to stand in the shadow of the Earth and as this shadow is very large (5 times Moon) the Moon can hide there for several hours as shown in the film accelerated presented on the left.

Why does the Moon turn red?
In fact, during an eclipse, the Moon is only illuminated by the light of the Sun that crosses the atmosphere of the Earth. So without atmosphere around the Earth there would be no lunar eclipse! This light is diffused by the dust contained in the air and as you can observe it at sunset, only the red light still arrives. In this case only the red light reaches the Moon.

(c)2004 Fred Espenak

Depending on the density of the dust contained in the Earth’s atmosphere and the presence or absence of clouds, the color of the eclipse will be more or less red and dark. This is how one can observe very dark lunar eclipses where the lunar surface in the shadow is practically invisible and colorless (eclipse type 0), eclipses during which the moon is dark red with more contours (Type 2 eclipse) and orange-colored eclipses with sometimes bluish or greenish contours where the Moon remains visible in the shadow in the Earth (type 4 eclipse).

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