M 81

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Observation place


TelescopePlanewave 431mm - 17 ″, 2mm FL, f / 939
MountParamount ME
Imaging cameraSBIG STL-11000M - regulated at -20o Celsius
Image typeL (RGB) (Vs for synghetic green)
ExhibitionLuminance (7 x 6,67 'bin 2 × 2), R and B (3 x 3' bin 3 × 3 each)
PretreatmentMaxim DL
TreatmentPhotoshop and PixInsight
Specific treatmentCreate a synthetic green image

Object description

Object typeSpiral galaxy
ConstellationBig bear
Visual magnitude6,9
Distance11,8 million light years
Diameter60000 light years
Dimension seen from Earth26,9 x 14,1 arc minutes
M81 is a spiral galaxy with a relatively modest diameter of 60000 light-years. In 1993, its observation by the Hubble telescope made it possible to estimate the distance of the galaxy at 11,8 million light-years, which makes it one of the closest to ours. This galaxy has a perfect spiral structure. It is part of the same group of galaxies as M82. This group is part of the Virgo supercluster, as is our local group. The core of the galaxy would house a black hole.  

A few tens of millions of years ago, which is relatively recent on a cosmic time scale, the galaxies M81 and M82 found themselves very close to each other. M81, larger and more massive, deeply deformed M82 by gravitational interaction. This encounter also left visible traces on M81, despite its size and brilliance, first by enhancing the overall appearance of its spiral arms and then in the form of a dark linear bar located in the lower left of the central core. The two galaxies are still close since the distance from their centers is only about 150000 light-years.  

In a site with little light pollution, M81 is clearly visible with binoculars due to its magnitude of 6,9. In a 114mm telescope, the nucleus appears bright and surrounded by a diffuse halo. A 350 mm instrument is needed to detect the spiral arms of the galaxy.  

In my image, which solves M81 very well, we can appreciate the great beauty of this galaxy which is presented in beige tones in its center and in blue tones on its spiral arms.   
Richard Beauregard
Sky Astro - CCD
My impression "We cannot be alone in this gigantic universe"