So far this is one of the most fascinating objects I have observed on the moon. These chains of craterlets were formed when rubble following the Copernicus impact rained down on Mare Insularum. At average seeing only the biggest craterlets were visible, but when the seeing stabilized the full range of the bombardment came into view. Just south of Copernicus (up in the sketch) is another Lunar 100 object, Copernicus H (L74). Notice also the barely visible sunken crater Stadius, above Eratosthenes.