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Meade RCX 400 16", SBIG 8Xme with AOL, ALT AZ mount with derotator
The HR diagrams for globular clusters M13, M5 and M3 shows stars distribution out of the main sequence, with few blue bright stars, proving the age above 10 billion years of these clusters. M3 appears specifically low in numbers of hot blue stars, one of the oldest cluster. I was inspired by your article in S&T of December 2010, from R.J.Vanderbei, "Sequencing the Stars", so I started pointing my scope to GCs and calculating their HR diagrams. All cluster's pictures were taken in the same night, with the same exposure (LRGB 30MIN total) and same elaboration, to allow comparison. Maxim DL for elaboration, Astroart for star identification and PS for final display. Plenty of fun...