M81

Messier 81 (M81), also known as Bode's Galaxy, is a grand-design spiral galaxy in the constellation Ursa Major. It lies about 11.8 to 12 million light-years from Earth (roughly 3.6 to 3.7 megaparsecs) and is one of the brightest galaxies visible from northern latitudes. M81 spans about 90,000 light-years in diameter and features a prominent, luminous central region with two well-defined spiral arms. The outer disk is rich in neutral hydrogen, and star formation is active along the arms.

Discovery and naming: M81 was observed by Johann Elert Bode in 1774 and later cataloged by Charles Messier as object 81, earning the designation Messier 81 or M81. It is a prominent member of the nearby M81 Group of galaxies.

Interactions and environment: The M81 Group includes nearby galaxies such as M82 (the Cigar Galaxy) and NGC 3077. Gravitational interactions among these members have distorted gas distributions and produced tidal features, including HI bridges linking the galaxies and influencing star formation histories within the group.

Observations and significance: M81 has been studied extensively across the electromagnetic spectrum and serves as a useful laboratory for understanding spiral structure, galactic interactions, and star formation. It hosted supernova SN 1993J, a well-studied Type IIb event. Distance estimates rely on standard candles such as Cepheid variables, contributing to calibrations of the extragalactic distance scale. The galaxy is observable with modest amateur equipment under good conditions.