M 81, M 82 and Galactic Cirrus
M 81 and M 82 were discovered by Johann Elert Bode in 1774. A few observers have reported that M 81 is visible to the naked eye under perfect conditions. M81 is the main galaxy of a galaxy group neighbored to the local group of galaxies.
The M 81 group of galaxy is quite similar to our local group.Central galaxy is the large bar spiral M 81.
M 82 is the brightest Infrared galaxy of the sky just 125,000 light years away from M 81. A close encounter of both galaxies took place about 600 million years ago. As a result star formation is still ongoing until today. Several Supernovae explosions have created strong winds that carry hot gas out of the center of the galaxy forming Hα filaments. The hot matter cools down and part of it falls back to the center again.On the other hand, M 81 shows no signs of the encounter.
East of M81 the galaxy UGC 5336 (Holmberg IX) appears as a weak patch of light. NGC 3077 can be seen near the edge of the image. Both galaxies as well as PGC 28731 belong to the M 81 group. Most of the other diffuse spots are remote galaxies in the background. The whole image is covered with a very faint nebula sometimes called IFN or Integrated Flux Nebula. Nevertheless “Galactic Cirrus” may be a better name for these faint structures that can be seen on many locations in the sky. They were discovered visually and photographically by Johann Georg Hagen in the 1930'years. It is believed that the galactic cirrus consists of gas and dust reflecting the light of our galaxy. Some of the faint clouds visible in the image are intergalactic rims between M 81 and M 82.
Very faint objects like the IFN can normally not be photographed from light polluted areas especially when the radiated light is more or less uniformly distrubuted over the visible spectrum. Only with a combination of a fast telescopes and very long exposure times such objects became visible.