Combination of 15, 3 minute images.
STL-1001E CCD. 20" f/6.8 Dall-Kirkham cassegrain at prime focus.
Abell 31 is a very large, and very low surface brightness planetary nebula in Cancer, about 3 degrees south of the open cluster M 67. The magnitude is quoted as 12.2, but the light is spread out over and area 16.2 arc minutes in diameter. No hint of the planetary was visible in a 17.5" telescope.
Abell planetaries have a reputatiuon of being some of the toughest objects for the visual observer and Abell 31 is a perfect example of this. It is even a tough challenge for the CCD imager. In the image below, only the vaguest hints of nebulosity are visible below left of the double star near the satellite streak. Yet there are a number of anonymous galaxies in the image, the brightest of which is fainter than 16th magnitude! Clearly much more exposure time is needed for this object.
