What does earthshine mean?
The photo of the Moon at the right shows a lighted crescent shape plus the remaining part of the Moon can barely be seen. This shadowy section of the Moon can be seen because of earthshine, which means a faint light reflected from Earth’s surface lights up the darkened part of the Moon facing Earth.
The diagram below shows how the direction of light that creates earthshine.
1. Sunlight strikes Earth
2. Sunlight is reflected from Earth’s surface to the Moon
3. Earthlight is reflected from the Moon’s surface back to Earth.
Each time light reflects off a surface it gets dimmer. This is because some of the light is absorbed by the reflecting surface. Because of this, earthshine is much dimmer than is moonshine. Earthshine is light that has been reflected twice (once off the Earth and once off the Moon), and moonshine is light that has been reflected once (off the Moon).
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