Spiral galaxy M101 is a giant with a diameter on the order of 170,000 light-years. It lies in the constellation Ursa Major the Great Bear some 23 million light-years away. 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. Discovered by Pierre Méchain on March 27, 1781, it was communicated to Charles Messier who verified its position for inclusion in the Messier Catalogue as one of its final entries.