M101 — The Pinwheel Galaxy

Twenty-one million light-years away — so far that the light in this image predates the entire evolutionary line that produced humans. The Pinwheel Galaxy is oriented almost perfectly face-on to us, revealing the full spiral structure that edge-on galaxies hide. The pink knots scattered along the arms are HII regions — clouds of hydrogen gas lit up by newborn stars. The blue patches are associations of young, hot stars. You’re looking at a galaxy roughly the size of the Milky Way, frozen in a moment 21 million years old.