At a distance of about 30 million light years from Earth, it is also one of the brightest spirals in the night sky. A composite image of M51, also known as the Whirlpool Galaxy, shows the majesty of its structure in a dramatic new way through several of NASA's orbiting observatories.
Volcanoes shaped the moon's surface until relatively recently. The bright areas are the ancient crust leftover from the moon’s formation, and the dark areas are the relatively newer, smooth plains that formed from all that lava that erupted from the interior. These dark plains are what are called maria, Latin for “seas.”