M101 is another prominent spring galaxy that I have wanted to do properly for a few years now. It was one of the first images I took with my equatorial mount and faster Newtonian, but I was still pretty green back then. This time, I took 33 hours of data over five nights. I had a dust mote that disappeared after the first two hours of data, which was a little strange, but I was able to fix that up.
UPDATE: My first processing of this image left something to be desired. After staring at it for a good while, I couldn’t help but wonder where all of the HII regions are. I went back through my processing step by step, and I found that PhotometricColorCalibration was the culprit. It really squashed all the colors out of the galaxy. I reprocessed the image using the regular ColorCalibration on the core of the galaxy, and I am much happier with the results.
M101 is a face-on grand design spiral galaxy 21 million light years away. It is just east of the end of the handle of the Big Dipper. Compared to other nearby galaxies, it is relatively faint, with an average surface brightness of 14.6 magnitude. Even with so much exposure, you can only begin to see the very faint ends of the spiral arms. It is quite large at 170,000 light years in diameter, and is estimated to contain one trillion stars. To the bottom left is a bright dwarf galaxy that is orbiting M101, NGC 5477.
Here is an annotation using the M, NGC, IC, and PGC catalogues,
Using the SDSS QSO catalogue, this image contains at least 100 quasars in the background. The farthest is SDSS J140053.75+543012.1, which has a redshift z = 4.26281. This gives it a light travel time of 12.277 billion years, and, as of right now, it is 24.460 billion light years away.
