The galaxy M101 (Messier 101, Pinwheel Galaxy) is a swirling spiral of stars, gas, and dust n the constellation of Ursa Major. It is about 70 percent larger than our own Milky Way galaxy, with a diameter of about 170,000 light-years, and sits at a distance of 21 million light-years from Earth. This means that the light we're seeing in this image left the M101 about 21 million years ago, many millions of years before humans ever walked the Earth. X-rays from Chandra (purple) show the hottest and most energetic areas of this spiral galaxy. Release date May 24, 2012.