Tycho and Copernicus: Lunar Ray Craters . ... But when the Moon is full some craters seem to sprout systems of bright radial lines or rays. This detailed digital close-up of the full Moon features two prominent ray craters , Copernicus (upper left) and Tycho (lower right), each with extensive ray systems formed of light colored debris blasted out by the crater-forming impacts. In general, ray craters are relatively young as their rays overlay the lunar terrain . ... NASA Official: Jay Norris. ...