From the LRO (Lunar Reconnaissance Orbiter), the phases of the moon occur once a month because of the change of the shadow depending on the location of the moon. Twice a year the moon darkens, turns red, and then turns normal. This is called a lunar eclipse.
The moon passes through the penumbra where light is partially obscured making a slight darkening of the moon. Then the moon can pass through the umbra where all direct sunlight is blocked from the moon. BUT WHY DOES THE MOON TURN RED? When light travels the side of the earth, the sunlight and its wavelengths go through a thick layer of Earth's Atmosphere. Short wavelengths, such as blue (~419 nanometers) get absorbed or scattered in the Earth's atmosphere, while the larger wavelengths like red (~559 nanometers) get left over to travel to the moon. This phenomenon can last from a few minutes to even a few hours. |
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