Hyginus (crater)
Hyginus is a lunar caldera located at the east end of the Sinus Medii. It was named after ancient Roman astronomer Gaius Julius Hyginus. Its rim is split by a 220 kilometer-long rille, Rima Hyginus, that branches to the northwest and to the east-southeast. The crater is deeper than the rille, and lies at intersection of the rille's branches. Together, the crater and the rille form a prominent feature in an otherwise flat surface. Smaller craters along the length of the rille may have been caused by the collapse of an underlying structure. Hyginus is  one of the few craters on the Moon that was not created as a result of an impact, and is instead believed to be volcanic in origin. It lacks the raised outer rim that is typical with impact craters. Hyginus was considered a possible landing site during the Apollo Program, because it was thought to be a site of potentially active volcanism. Satellite craters. By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Hyginus.