M51-The Whirlpool Galaxy
Size: 11 x 7 arc minutes
Constellation: Canes Venatici (The Hunting Dogs)
RA: 13h 29.9m
Dec: +47° 12'
M51 is a large, spiral galaxy colliding with a smaller cousin. Thick dust lanes spiral outward from M51's nucleus. One of these dust lanes partially blocks the light from the upper third of the companion galaxy, attenuating the light and coloring it reddish-brown. Careful inspection of the spiral arms in M51 reveals small, bluish knots of light. Some of these features are believed to be globular star clusters similar to our Milky Way's M13.
M51's total mass is estimated to be about 160 billion suns, and its diameter is about 100,000 light years. Its total luminosity is about 10 billion suns.