Bailly (crater)

This class of formation is known as a peak ring basin, which has a single interior topographic ring or a discontinuous ring of peaks with no central peak.^[10] It is the largest crater on the near side of the Moon. In area it is comparable in size to a small mare. It lies north of the crater Le Gentil and east of Hausen.^[11]: 136 Further west of Bailly are the (unofficially named) Montes Dörfel mountains.

Due to the size and the worn state of this crater, it is estimated to be more than 3 billion years old, and is part of the Nectarian system.^[3][4] Bailly's uneven crater floor has remained free of basaltic flooding, and it is covered with a multitude of ridges and craters. The entire crater has been battered and worn, and the outer ramparts are eroded and in some places have even been worn away by myriad impacts. It likely is covered by ejecta from Hausen crater.^[12] If Bailly ever possessed a central peak, it is no longer discernible. However, the battered remains of a peak ring is possible.^[13][6] Due to its current condition, observers have termed this walled plain a 'field of ruins'.^[7]

The south-eastern part of the crater is home to two notable craters, designated Bailly A and Bailly B.^[8] These craters overlap, and Bailly A lies across the rim of Bailly's mountainous wall. Selenographer Giovanni Battista Riccioli named Bailly B, Bartolus for fellow Ferrarese Jesuit Daniello Bartoli (1608-1685) in his Almagestum novum (1651).^[9]: 211 The name was not recognized by the IAU.

By convention the following features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Bailly.^[14]