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31. M92 open cluster in Hercules
Notes: Wikipedia puts the age of M92 at 14.2±1.2 billion years, which makes it as old as the universe itself (en.wikipedia.org/wiki/Messier_92) and possibly older than the Galaxy (en.wikipedia.org/wiki/Milky_Way). The age is estimated from the very low percentage of iron in the stars. The cluster is located 16,000 light years from the Galactic plane and 33,000 light years from the Galactic center. These figures put it well within the halo of the Galaxy. One wonders how an older cluster would end up within the younger Galaxy. We suppose that it is actually the same age, or that it wandered into the Galaxy's gravity field and was captured.
Technical notes: The night was clear and quiet. There was a gibbous moon in the SE at 8:40 pm. M92 was in the west. Longer subexposures would bring out more stars, but longer subs create difficulties. Doubling the time from two to four minutes for 30 subs could mean that the scope will tip over the mid point of the mount and require slewing and recalibration of the guiding. Depending on when one begins imaging, it might crowd the time needed for shooting darks. It generally means staying up later to attend to the position of the mount and make sure that it is guiding properly. Long sessions can be wearing if done for several nights in close succession. The small image below was created by taking a second set of 4 min subexposures, making a stack, and stacking this stack with the 2 min stack after norming the intensities of the two stacks. A few more stars are visible, but the washout in the core is enlarged. It seems the only way to get even intensities is to cut and paste the better parts of multiple images.
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