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 ("The Moon"). Franz also gave the mare its name, the "Eastern Sea", as it was located on what the convention at the time considered was the eastern side of the Moon
as viewed from Earth, though it is the western side as viewed by an astronaut walking on the Moon. 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
Hugh Percy 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 (pp. 133–135). ==Gallery==