Messier 81 is a spiral galaxy located in the constellation Ursa Major. It was discovered at the Berlin Observatory by Johan Bode on December 31, 1774.
Johan also discovered Messier 82 that same evening. It is just 38 arc min or bit more than eyepiece field north of M81. M82 is an irregular, disk galaxy which we view edge on. It was perhaps distorted by an encounter with Messier 81. In large aperture scopes, a prominent dark lane of dust may be seen crossing the irregular core. Bright knots and additional short, dark lanes are also visible.
In infrared light M82 is the brightest galaxy in the sky. It is also prominent in radio telescopes. The galaxy has an unusually high rate of star formation and is an excellent example of a star burst galaxy.
It is included in Halton Arp's list of peculiar galaxies. If you are interested in viewing this and other fascinating galaxies see the Arp Peculiar Galaxy Observing Club.
Image Credit: Alan Jeeter, Longmont Astronomical Soceity http://allenjeter.com/AllenAstro/Welcome.html