M31, The Andromeda Galaxy

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Published also on APOD!
The Andromeda Galaxy is the most wonderful galaxy in the sky, excluding our Milky Way. It lies 2.5 million light years from us and is visible by naked eye even under moderately light polluted cities. This image was obtained at about 1 meter focal length and the camera was rotated so that the galaxy lies on the diagonal; however its external arms are a little outside the corners.

Technical Data
Optics TEC 140
Focal Length
 1011 mm
Focal Ratio f/7.2
Exposure Time 2 h 44 min (composed of 15 exposures of 10 min, plus 7 exps of 2 min at reduced ISO for the bulge)
CCD Canon EOS 5D with Baader filter
Sensitivity 800 ISO (10 min subs) and 400 ISO (2 min subs)
Location Bogli (PC, Italian Apennines) at 1350 m height
Date
 16 November 2012
Mount Gemini G-41
Tracking Lodestar on an 80mm f/5 refractor
Temperature and humidity T= -2 °C, RH=45%
Sky brightness at zenith (with SQM-L) 21.2 mag/arcsec^2
Notes North at top-left. Very good sky over a layer of clouds at about 1000 m height.

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