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M 81  (NGC 3031),  In  Ursa  Major


     M81 was discovered in 1774 and, with M82, is one of the brightest in its galaxy group. A low resolution film image of both M81 and M82 may be seen here. These galaxies are outside the local galaxy group, lying approximately 10-12 million light years away. M81 is 24 x 13 arc minutes in size and relatively bright at 6.9 visual magnitude. Its absolute size is estimated at 70,000 light years diameter and equivalent to 17 billion suns in luminosity. Compared to M31 and M51, it is relatively low in contrast, so the spiral arms are rather faint.

The above image  involved luminance enhancements in MaxIm, followed by combination with RGB in Photoshop. Luminance enhancements included histogram linearization, DDP, and unsharp masking. Note the additional detail brought out by this processing compared to the image below. This image would still benefit from additional exposure time to increase the signal-to-noise ratio. For full details see table at the bottom of the page.

An earlier version from the same data (below) was created with all enhancement (levels, curves) carried out in Photoshop:

 Date  2002-04-12

 Astro-Physics 130 EDF at f6 on A-P 1200GTO mount; ST-4 guiding

 Meade 416XTE CCD camera with 616 color wheel controlled with MaxIm DL/CCD v3           

 Exposures  L=12x300 sec, R=10x300 sec, G=10x300 sec, B=10x300 sec, all unbinned      

 Calibrated in AIP4WIN, assembled in MaxIm, stretched and unsharp masked in PhotoShop. 

 Additional processing in the second image as described above the image. R, G, and B frames were

 weighted 1:1:2.5.