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NGC 6791

NGC 6791 is one of the most studied open clusters in the sky. This object lies in the constellation Lyra the Harp and has a mass of about 5,000 times that of our Sun. It is an old cluster, at about 8 billion years, but it contains some unusual younger stars (4 and 6 billion years old). It is also metal-rich (“metals” in astronomy refer to elements other than hydrogen and helium); old open clusters are usually metal-poor. It covers an area about half the width of the Full Moon. Look around the cluster, and you’ll spot a few galaxies that lie far in the background. (10-inch Astro Systeme Austria astrograph at f/6.8, SBIG STL-11000M CCD camera, RGB image with exposures of 110, 110, and 90 minutes, respectively)
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