M101, also known as the Pinwheel Galaxy, is a spiral galaxy located approximately 21 million light-years away in the constellation Ursa Major. It is one of the most prominent galaxies in the night sky and is notable for its well-defined spiral arms and bright core. M101 is classified as a type Sc spiral galaxy and has a diameter of about 170,000 light-years. Discovered by the French astronomer Pierre Méchain in 1781, M101 is part of the M101 Group, which includes several other galaxies. It is often studied for its active star formation regions and contains numerous H II regions, where new stars are born. M101 is also a popular target for amateur astronomers due to its striking appearance.