Sinus Medii

Sinus Medii (latin for "Bay of the Center") is a small lunar mare that is located at the intersection of the Moon's equator and prime meridian. As seen from the Earth, this feature is located in the central part of the Moon's near side, and it is the point closest to the Earth. From this spot the Earth would always appear directly overhead, although the planet's position would vary slightly due to libration.

This plane was given the latin name for "Central Bay" by Johannes Mädler. The selenographic coordinates are, and the diameter is 335 km. It joins Mare Insularum in the west with Mare Vaporum to the north.

The eastern part of this area is notable for a series of rille systems. In the far northeast is the Rima Hyginus, which is bisected by the crater Hyginus. At the far eastern end is the 220-km long Rima Ariadaeus rille which continues eastward to the edge of the Mare Tranquillitatis. Crossing the prime meridian longitude is the Rimae Triesnecker rille system, named after the crater Triesnecker just to the west.

The northern edge of the Sinus Medii is formed by a highland region, with the impact craters Murchison and Pallas along the border. Near the northern border on this mare is the cup-shaped Chladni.

Another highland region lies to the south and southeastern edge of the Sinus Medii. Several flooded craters lie along this border, with Flammarion near the western edge, then Oppolzer, Réaumur, and Seeliger further east. The Rima Flammarion and Rima Oppolzer rilles lie along the edge of the mare near their corresponding craters. Also along the southeast border and bisecting the prime meridian is the crater Rhaeticus.

In the western half of the interior are the small craters Bruce and Blagg. To the west-southwest of Bruce on the mare floor are the landing sites of the Surveyor 4 and Surveyor 6 missions. Near the western end of the mare are the flooded craters Schröter and Sömmering.