Looking for a sky event this week? Check out our full Sky This Week column. February 21: A ghostly planetary nebula A lovely crescent Moon is visible nearly all evening, setting around local midnight.

Low, winding ridges run across the Moon’s dark plains like faint seams in cooled wax. They are easy to miss in a wide photo.

In A Nutshell Scientists have mapped 2,634 fault segments across the Moon’s volcanic plains that could generate moonquakes These faults are consistent with shallow moonquakes detected by Apollo ...