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Why do the lunar maria look dark when viewed from Earth?
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Moon
(Left) Near side of Earth's Moon, photographed by the Galileo spacecraft on its way to Jupiter. (Right) Far side of the Moon with some of the near side visible (upper right), photographed by the Apollo 16 spacecraft.
The lunar maria appear dark when viewed from Earth because they are composed of basalt, a dark-colored volcanic rock.12
These features are vast, low-lying plains formed billions of years ago when massive impact basins were flooded by fluid lava originating from the Moon's interior. Unlike the brighter, heavily cratered lunar highlands, which consist of older, lighter-colored material, the maria represent younger volcanic plains. The contrast between these dark basaltic regions and the lighter highlands creates the distinct patterns visible to the naked eye from Earth, often referred to as the "man in the moon."134