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From time to time, the Moon (or a portion of it) enters the Earth's shadow in what is known as a lunar eclipse .The Moon is dimmed partially or almost completely, depending on whether it passes through the less dark part of the Earth's shadow, the penumbra , or the darker part, the umbra .

The Lunar Prospector relied on sunlight to recharge its batteries. Scientists were concerned that whenever the Lunar Prospector was in the darkness of the Earth's shadow, its batteries could have drained to the point where they could not be recharged.

Prospector survived penumbral lunar eclipses on September 6, 1998, and January 31, 1999, without damage. It also survived a much darker umbral eclipse the following July.

Graphic of a lunar eclipse

In a video interview conducted just before the eclipse of September 6, 1998, Dr. Alan Binder, Principal Scientist for the Lunar Prospector, discusses steps scientists took to protect the spacecraft.

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