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32. NGC 7331 spiral galaxy
Notes: The image combines sets from three nights for a total of 9 hours. This nameless spiral galaxy is the most distant deep sky object we have imaged. About the size of the Milky Way, it has it's own cluster of galaxies. The stars you see are all in our own galaxy, no more than about 75 thousand light years distant, so we see NGC 7331 through a light veil of stars. If you zoom in, you can see three or four galaxies just above it, another cluster of three or four in the lower left corner, and others scattered here and there. We mapped 19 including NGC 7331. There is a beautiful little face-on spiral near the upper left corner. The little cluster including NGC 7317-20 is known as Stephan's Quintet. NGC 7318B has fallen into the middle of the group and created a shockwave. It appears that a bit of this wave can be seen at the top of NGC 7318B in our image. The numbers on the axes of the map refer to pixels. We have also plotted the galaxies on the coordinates of declination and right ascension, creating an atlas map for the NGC 7331 sector.
We can use the visible galaxies to make our own estimate of the number of galaxies in the universe. Depending on what assumptions we make to calculate the distances to the farthest ones and the volume of space that they occupy, it comes to 40 to 100 billion. This is based on an estimated diameter of the universe of 93 billion light years. It is claimed that Hubble is capable of detecting 80 billion galaxies. The number is based on extrapolations from counts made in Hubble's field of view, which is a tiny fraction of the total volume of the universe. Our even tinier fraction agrees within an order of magnitude and brackets the Hubble estimate. And it cost only one millionth as much to obtain. See (27) for more on galaxy distances.
Technical notes: We used the Wikisky Site (Inhabited Sky tab) to find a map of the neighborhood of NGC 7331. Our map is rotated 90 degrees clockwise from the Wikisky map, which has the appropriate orientation for reading declination and right ascension. The identifications were made using this map. Our #11 does not appear on the Wikisky map. Their map also has three objects (PGC 141041, 214856, and 2045849) that don't appear on our map.
The sky was clear and dark. The guide scope is slightly defocussed. The PHD integration time was set to 1. Our polar alignment was good, but seemed to grow worse with time. We can detect no effect on the tracking, which has been good since we adjusted the position of the telescope on the mount to shift the weight slightly to the camera end. Zoom in/out with ⌘↑(+/-) (Mac), ctrl (+/-) (PC).