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 and well-defined spiral structure, making it a popular target for amateur astronomers. The galaxy has a diameter of approximately 170,000 light-years, which is about 1.5 times larger than our Milky Way. Discovered by the French astronomer Pierre Méchain in 1781, Messier 101 is classified as a type Sc spiral galaxy. It contains numerous bright star clusters and regions of active star formation, contributing to its striking appearance. The galaxy is also part of the M101 Group, which includes several other galaxies.