earthshine

American  

[urth-shahyn] / ˈɜrθˌʃaɪn /

noun

Astronomy.

1. the faint illumination of the part of the moon not illuminated by sunlight, as during a crescent phase, caused by the reflection of light from the earth.

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earthshine British  

/ ˈɜːθˌʃaɪn /

noun

1. the ashen light reflected from the earth, which illuminates the new moon when it is not receiving light directly from the sun

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Etymology

Origin of earthshine

First recorded in 1825–35; earth + shine ¹

Explanation

Imagine yourself standing outside at night, staring up at the crescent moon. The dark portion is faintly lit by earthshine, the reflection of sunlight from the earth back to the moon. If you were standing on the moon looking at Earth, our planet would appear much brighter than the moon does to us from Earth. This is because Earth is covered in clouds, ice, and water, which are excellent at reflecting sunlight. This reflected light travels through space and hits the moon, creating earthshine. Earthshine is most visible during a thin crescent moon. Historically, it was called "the old moon in the new moon’s arms," because you can see the ghostly outline of the full circle even when only a sliver is sunlit.

Example Sentences

The answer’s in the name of this phenomenon: earthshine.

From Scientific American • Jul. 21, 2023

While the sun doesn’t shine there, Earth can, and it’s possible to use earthshine to look for water ice in the bottoms of these craters.

From Scientific American • Jul. 21, 2023

By measuring the sunlight reflected from Earth to the dark part of the moon at night, scientists measured what they call "earthshine" or albedo - basically Earth's reflectiveness.

From BBC • Nov. 11, 2022

Dr. Adams last week told how he finessed this physical difficulty by using earthshine.

From Time Magazine Archive

When the sun was below the horizon, the surface was either barely visible if it was in earthshine, or totally invisible in a black void if there was no earthshine.

From "Flying to the Moon: An Astronaut's Story" by Michael Collins