Sunlight that falls on a body in the solar system is partially absorbed and partially reflected. The reflected fraction is known as the albedo and is expressed as a decimal number. A high albedo doesn't mean an object appears bright in our sky. For example, the albedo of Mars is .15, yet despite its brightness, the albedo of the moon is only .07. Stated simply, that means the surface of the moon is inherently darker than that of Mars.

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