The Pinwheel Galaxy (also known as Messier 101, M101 or NGC 5457) is a face-on spiral galaxy distanced 21 million light-years (six megaparsecs) away from Earth in the constellation Ursa Major. It was discovered by Pierre Méchain on March 27, 1781 and was communicated to Charles Messier.
M101 is a large galaxy, with a diameter of 170,000 light-years. By comparison, the Milky Way has a diameter of 100,000 light years. It has around a trillion stars, twice the number in the Milky Way