Sosigenes (crater)  Sosigenes is a lunar impact crater on the west edge of Mare Tranquillitatis. Its diameter is 17 km. It was named after ancient Greek astronomer Sosigenes of Alexandria. It lies to the east of the large walled plain Julius Caesar. The crater rim has a high albedo, making it relatively bright. It has a small central rise at the midpoint of the floor. To the east on the mare is a formation of parallel rilles designated the Rimae Sosigenes. These follow a course to the north, and have a length of about 150 kilometers. The small, bowl-shaped crater Sosignes A lies across one of these rilles. By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Sosigenes.