Craters appear on most bodies on the Solar system and primarily stem from the period of bombardment from between 3 and 4 billion years ago. Only very few of the Moon's craters are candidates for a volcanic origin.
Tycho and Copernicus are the 'source' for bright rays.The longest ray from Tycho can be seen more than halfway across the disk. These rays are best seen at Full Moon.
Copernicus wa formed 900 million years ago, probably by a small body about 5 km in diamtere stiking at between 10-30 km/sec. The crater was probably formed within less than two minutes.
There are two particularly prominent ray systems - those of Tycho and Copernicus. All craters have these features originally but they get 'washed out' after time. They are best viewed at full Moon.
Some of the polar craters are very deep in comparison with lunar craters in general and their floors are always in shadow. Thier tempertures could be as low as 40-50K. The Aitken Basin, which contains the South Pole, is the largest and deepest on the Moon - 2400 km wide and 13 km deep.
Impact theory Franz von Paula Gruithuisen