M101
Messier 101 (M101), also known as the Pinwheel Galaxy, is a face-on spiral galaxy approximately 25 million light-years away in the constellation Ursa Major. Spanning about 170,000 light-years, it is nearly twice the size of the Milky Way and is characterized by its grand design spiral structure.
Source: science.nasa.gov
APODs including "M101"
M101: An Ultraviolet View Credit:
08/06/1997
This giant spiral galaxy, Messier 101 (M101), was photographed by the Ultraviolet Imaging Telescope (UIT). UIT flew into orbit as part of the Astro 2 mission on-board the Space Shuttle Endeavour in March 1995. The image has been processed so that the colors (purple to white) represent an increasing intensity of ultraviolet light. Pictures of galaxies like this one show mainly clouds of gas containing newly formed stars many times more massive than the sun, which glow strongly in ultraviolet light. In contrast, visible light pictures of galaxies tend to be dominated by the yellow and red light of older stars. Ultraviolet light, invisible to the human eye, is blocked by ozone in the atmosphere so ultraviolet pictures of celestial objects must be taken from space.