M101

M101, also known as the Pinwheel Galaxy, is a face-on spiral galaxy located in the constellation Ursa Major. It is approximately 21 million light-years away from Earth, making it one of the closest large galaxies to our own Milky Way. M101 is classified as a grand design spiral galaxy, characterized by its well-defined spiral arms.

The galaxy spans an impressive 170,000 light-years in diameter, making it larger than the Milky Way. Its spiral arms are studded with numerous bright H II regions, which are areas of active star formation. These regions give M101 its characteristic appearance of having many bright knots and extensions along its arms. The galaxy's total mass is estimated to be around 100 billion times that of the Sun, with a significant portion of this mass likely being dark matter.

M101 was discovered by Pierre Méchain in 1781. It is a popular target for amateur astronomers due to its brightness and size, though its low surface brightness can make it challenging to observe under light-polluted skies. The Pinwheel Galaxy has been the subject of extensive study, providing valuable insights into galactic structure, star formation processes, and the distribution of matter in the universe. Its relatively close proximity allows astronomers to study its features in great detail, contributing significantly to our understanding of galactic evolution.