M82: An Irregular Galaxy

Explanation: Not all galaxies have spiral structure like our Milky Way. Many have smooth elliptical shapes, but also many have irregular shapes such as the bright sky object M82, the 82nd object on Messier's list. The strange structure of this galaxy is thought to be caused by young stars ejecting gas in energetic bubbles, and by lanes of absorbing dust.

For more information on M82 see The Electronic Universe Project's write-up. Many images of Messier objects can be found in The Electronic Universe Project's The Galaxy Gallery: Messier Objects. Many images of Messier objects can be found in The Electronic Universe Project's The Galaxy Gallery: Messier Objects.