Messier 31, the Andromeda Galaxy is the closest spiral galaxy to the Milky Way. It is also, I believe, the farthest object from Earth that can be seen with the naked eye. This time of year, if you look to the East North-East you will see the constellation of Andromeda. From even a slightly dark site, you can see a smudge of light which is M-31. With a modest pair of binoculars, you can see M-31 stretch across the whole field, as well as its companions M-32 and M-110.

You would think that it being such a bright object, it would be easy to get a photograph of M-31, and you would be right. Getting a good photograph of it is another story. First off, it's huge compared to other astronomical objects. The photo below was taken at a relatively short focal length of 685mm, and it still fills the frame. Not only is it huge, it's got a very large dynamic range. Which means if you get the fine details of the spiral arms, you tend to completely overexpose the core. Expose for the core and details are hard to bring out. Getting a good photograph of M-31 is all about balancing the exposures between the core and outer arms.

I hadn't tried to photography M-31 with the CCD camera, so I just took a stab at the proper exposures. Still without a luminance filter, I had to substitute Hydrogen Alpha. This is a composite of twenty 2-minute exposures for each channel, hAlpha, red, blue and green. I blended the hAlpha and red images to bring out the red, star forming regions that can be seen in the outer arms. Also, the Ha and red were blended for the luminosity channel.

Date: August 7, 2010
Location: Sugar Grove Nature Center, Funk's Grove, Illinois
Telescope: AT106LE, AT2FF
Camera: SBIG ST8300M, FW5-8300
Filter: Baader hAlpha, RGB
Mount: Celestron CGE
Guider: Orion ST80, SSAG
20 X 120 seconds, each channel Ha,R,G,B
Individual channels stacked in Deeps Sky Stacker
Red channel blended with hAlpha for red and luminosity using Photoshop CS4