An Etymological Dictionary of Astronomy and Astrophysics
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An area on the surface of the → Moon that appears darker and smoother than its surroundings. Once thought to be seas, lunar maria are now known to be basaltic basins created by volcanic → lava floods; plural maria.

→ lunar; L. mare "sea," plural form maria, because Galileo thought the dark featureless areas on the Moon were → seas.