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16. M101, Pinwheel Galaxy
Notes: See 15 for notes on the galaxy and the four companion galaxies visible in this image. This is the same subject as 15, but taken with 34 sub-exposures at 7 minutes each. Compare to 9 sub-exposures at 17 minutes each for 15. The longer sub-exposures in 15 revealed more detail in the spiral arms and in the companion galaxies. There appears to be much more noise in this image. Also, the stars are rounder, but still not perfect. We reduced the sampling intervals of the guide camera from 2.0 sec to 0.5 sec. This seemed to result in better tracking, but we are still getting a bit of periodic error which appears to be backlash on the RA axis. The guide star was faint and we had to recapture it twice. There was no moon. Zoom in/out with ⌘↑(+/-) (Mac), ctrl (+/-) (PC).