M81 and M82 - Galaxies in Ursa Major

M81 - Spiral galaxy in Ursa Major. N.A.Sharp/ NOAO/AURA/NSF [larger image]

M81 is an outstanding Sb spiral galaxy in Ursa Major. Although its magnitude of 7 makes it bright enough to be visible in 7x50 binoculars in suburban skies, M81 it is pretty hard to find because it is located far from any handy reference stars. To find M81 start with a line drawn from Phecda to Dubhe, two bright stars in Ursa Major. Extend that line past Dubhe for the same distance you just traversed, this route passes to within a degree of M81. Watch for 24 Ursae Majoris lying at the right angle of a small triangle. The triangle points southeast and almost directly to M81, just two degrees away.

M81 is an example of a starburst galaxy undergoing a period of rapid star formation. Even in a small telescope it looks disturbed, and in larger instruments it is highly mottled with several bright knots visible.

Found within the same low-power eyepiece field as M81 is M82, a peculiar edge-on galaxy. Although it is a magnitude fainter than its neighbor, M82 offers more structural detail. The most prominent feature is a rift of darkness across its center. Several other dark filaments can be spotted throughout M82, but you need a large telescope for that.

Finder map - field width 15 degrees, stars to magnitude 10.5.