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Messier 81 and 82

Interacting Galaxy Pair

 

M81: R.A. 09h55m33.1s Dec. +6903'56 (2000)
Magnitude 7.8, 21.9' x 10.5'

Distance: 12 myr

M82: R.A. 09h55m52.4s Dec +6940'47" (2000)
Magnitude 9, 9.3' x 4.4' 
Distance: 12 myr

Minimum requirements to detect: any telescope

This famous pair of galaxies is worth looking at again and again. Discovered by Bode in 1774, tthese 7th and 9th magnitude galaxies are fine objects in any telescope, even binoculars.

M81, which is also known as Bode's Nebula (and NGC 3031), is a nearly face on spiral galaxy that spans 25' x 12'. Look for a bright central condensation with a nearly stellar center. Large aperture scopes with wide fields of view may reveal the wispy spiral arms that surround the bright portion of the galaxy.

M82 (NGC 3034) is a nearly edge-on irregular spiral galaxy that spans 10' x 5'. In telescopes smaller than 10" this galaxy appears to be a normal spiral. Larger instruments may reveal bright knots cut by dark lanes.

I observed M 81 & M 82 in my 18-inch Dob. Here are my notes from that session:

M81 & M82 cleared the tree to my northeast and I had a look for the first time in my 18-icnh. I've observed these galaxies in all sorts of instruments, including some much larger, but once again I was stunned by the view in my 18-inch. I don't know if its my location or what, but I've never seen so much detail in M82 before. It was like a photograph. I couldn't get over the contrast in the dust lanes! Whatever the reason, I know I'm very lucky to have such access to the sky from my own back yard. M81 was it's usual, large, smooth self. It may be sort of boring, but if you think about it there is a certain beauty to its regular smoothness.
The observation of rapidly expanding filaments of gas in M82 galaxy lead to the controversial idea of "exploding galaxies" in the late 1970's. This idea, which was quickly abandoned, spawned at least one science fiction story.  We now understand M82 as a Starburst galaxy that is interacting with its neighbor, M81. These two galaxies share a common envelope of neutral hydrogen gas. A Starburst galaxy is a galaxy that has been triggered to form large numbers of stars, typically due to a collision or interaction with another galaxy. In computer simulations, when two galaxies collide the tiny stars simply pass right by one another, but the giant molecular gas clouds from which stars form actually collide. Collisions between giant molecular clouds can occur when two galaxies pass through one another or as a result of gravitational interaction between two nearby galaxies.

The exact interaction is still unknown, but it appears that the gas clouds in M82 have been colliding. The resulting shocks have  triggered a burst of star formation at a much higher rate than in a normal spiral galaxy. Hot, massive, but short-lived stars abound, making the newly formed star clusters much brighter than those found in our own galaxy.


The view in a 6" at 50x. North is down, East is to the right.

Millennium Star Atlas Vol II Chart 538
Sky Atlas 2000 Chart 2
Uranometria 2000 Vol I Chart 23