Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2000 December 28 Moon Mare and Montes Credit & Copyright: Peter Armstrong

Explanation: This arresting image of the third quarter moon in the excellent skies above the Pine Crest Farm Observatory, Dell Prairie, Wisconsin, was recorded with a 24 inch telescope and digital camera on October 19. Marvelously detailed, especially along the terminator or shadow line between lunar night and day, this cropped version of the full mosaicked image shows the cratered north polar region (top) and the broad smooth Mare Imbrium. Notable at the northern edge of the Mare Imbrium (Sea of Rains) is the 95 kilometer wide dark crater Plato, while the dramatic straight "cut" to the right of Plato, (toward the terminator) is the Vallis Alpes (Alpine Valley). The long, graceful arc of the lunar Montes Apenninus (Apennine Mountains) in the lower portion of the image sweeps southward along the boundary of the mare toward the left and ends near the bright ray crater Copernicus at the picture's edge. In 1971, Apollo 15 landed near the gap beyond the opposite (northern) end of the Montes Apenninus arc.