Byrgius is a lunar impact crater located in the western part of the Moon, near the limb. As a result, Byrgius appears strongly oval in shape due to foreshortening. To the northwest is the nearly ruined crater Lamarck. The rim of Byrgius is worn and eroded, with Byrgius A overlying the eastern rim and Byrgius D lying across the northwest. The floor is relatively flat and undistinguished by significant craters. Byrgius A possesses its own ray system that extends for over 400 kilometres. The crater is named after Jost Bürgi.
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