The
lunar maria (singular:
mare ) are large, dark,
basaltic plains on
Earth's
Moon, formed by ancient
volcanic eruptions. They were dubbed
maria,
Latin for "seas", by early astronomers who mistook them for actual
seas. They are less reflective than the "highlands" as a result of their iron-rich compositions, and hence appear dark to the naked eye. The maria cover about 16 percent of the lunar surface, mostly on the side visible from Earth. The few maria on the far side are much smaller, residing mostly in very large craters. The traditional nomenclature for the Moon also includes one
oceanus (ocean), as well as features with the names
lacus (lake),
palus (marsh), and
sinus (bay). The last three are smaller than maria, but have the same nature and characteristics.