Messier 109, NGC 3992

Messier 109 is a barred spiral galaxy in the constellation Ursa Major.

Messier 109 was discovered by Pierre Mechain in 1781. In 1783, Charles Messier listed it as his 109th object, but this was not widely accepted as part of the "official" Messier catalog until the 1950s. William Herschel found M 109 independently in 1789, and cataloged it as H IV.61 (incorrectly classifying it as a planetary nebula); from this it entered the New General Catalog as NGC 3992.

M 109 can be seen a hazy spot situated 40' SE of the star γ UMa (Phecda). The galaxy is about 7.5' x 4.5' arc minutes in angular extent, and is of visual magnitude 9.6. Only its bright central region (with the bar), can be seen visually, and appears pear-shaped in smaller telescopes. The inner halo is mottled, and surrounds an irregular bright oval core. M 109 is one of the "Theta"-like barred spirals, classified as Hubble type SBc.

M 109 is about 84 million light years distant, and is receding at 1142 km/sec. It is the brightest galaxy in the Ursa Major Cluster, a group of galaxies identified in 1996 that is over 55 million light years away, and may contain over 79 members. M 109 has three satellite galaxies: UGC 6923, UGC 6940 and UGC 6969.

A type Ia supernova occurred in M 109 in 1956, and reached magnitude 12.3 or 12.8 at maximum brightness. SN 1956A was the only supernova observed in M 109 since its discovery.