The Pinwheel Galaxy (also known as Messier 101 or NGC 5457) is a face-on spiral galaxy distanced 25 million light-years away in the constellation Ursa Major, first discovered by Pierre Méchain on March 27, 1781, and communicated to Charles Messier who verified its position for inclusion in the Messier Catalogue as one of its final entries. M101 is a relatively large galaxy compared to the Milky Way. With a diameter of 170,000 light-years it is nearly twice the size of the Milky Way. (Wikipedia)