Geology
The selenographic coordinates of Sinus Medii are 2°24′N 1°42′E / 2.4°N 1.7°E / 2.4; 1.7, and its 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. Near the western end of the mare are the flooded craters Schröter and Sömmering.
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