Messier 101, also known as the Pinwheel Galaxy, is a spiral galaxy located about 21 million light-years away in the constellation Ursa Major. It is notable for its large size, with a diameter of approximately 170,000 light-years, making it one of the largest galaxies in the Local Group. Discovered by Pierre Méchain in 1781, Messier 101 contains several prominent features, including bright star clusters and regions of active star formation. Its spiral arms are rich in gas and dust, which contribute to the ongoing birth of new stars, making it a fascinating object for astronomers studying galaxy formation and evolution.