Mare Orientale - Discovery and Name

Discovery and Name

Mare Orientale is difficult to observe from Earth, as it lies at the extreme western edge of the near side. All that can be seen are the rough mountain ranges - the Montes Rook and the Montes Cordillera - and some glimpses of the dark mare material beyond them. However, the Moon's libration means that on rare occasions Mare Orientale is turned slightly more toward the Earth, and becomes a little more discernible.

Although various astronomers had observed hints of the mare, it was first fully described by the German astronomer Julius Franz in his 1906 book Der Mond ("The Moon"). Franz also gave the mare its name. At the time, it was located on what by convention was considered the eastern side of the Moon, hence Franz named it the "Eastern Sea". In 1961, however, the International Astronomical Union adopted the astronautic convention for East and West on the Moon and this limb became the western edge.

The first detailed study of the Mare Orientale was by H.P. Wilkins, who called it "Lunar Mare X". Franz's discoveries were not well known, and in the 1976 edition of his book Guide to the Moon, Patrick Moore claims that he and Wilkins discovered and named Mare Orientale in 1946. However, Moore credits Franz as discoverer in his 2009 Yearbook of Astronomy (p.133-135).