Hubble Legacy Archive, ESA, NASA; Processing and additional imaging - Robert Gendler
There's no denying it - galaxies are beautiful. M101, also know as the Pinwheel Galaxy, is a particularly sexy set of spiral arms and is 170,000 light-years across (twice the size of our own humble milky way).
The red marbling comes from hydrogen gas and occurs in areas where new stars are formed. The white and blue lights are stars and dust and, behind them, background light and galaxies.
M101 is in the constellation Ursa Major, know to me as a child as the Big Dipper or the Plough which can be seen through most of the year in the northern hemisphere.
Mostly though, it's pretty.