Twice a year, the moon turns 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 a lunar eclipse. Sometimes, when it is the full Moon and our satellite is perfectly aligned in the Earth-Sun axis, the Moon is placed in the shadow of the Earth and as this shadow is very large (5 times larger than the Moon) the Moon can hide there for several hours.

Earth’s atmosphere extends about 50 miles (80 km) above Earth’s surface. During a total lunar eclipse, when the moon is submerged in Earth’s shadow, there is a circular ring around Earth – the ring of our atmosphere – through which the sun’s rays pass.

Unlike a solar eclipse, which can only be viewed from a relatively small area of the world, a lunar eclipse may be viewed from anywhere on the night side of Earth.

In fact during an eclipse, the moon is only illuminated by the light of the sun which 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 happens to us. In this case only the red light reaches the Moon.

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 the very dark lunar eclipses where the lunar surface plunged into the shadow is practically invisible and colorless (eclipse of type 0), eclipses during which the moon is dark red with more contours. or less clear (eclipse of type 2) and eclipses of orange color with contours sometimes bluish or greenish where the Moon remains visible in the shadow in the Earth (eclipse of type 4).


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