M3, which is about 34,000 light-years from us, contains an estimated 500,000 stars packed into a 220 light-year space. M3 is notable for having more variable stars than any other cluster, at least 274 of them. While it is estimated to be 8 billion years old, there are surprising numbers of "apparently" young blue stars. M3 and M13 are similar in many respects, including chemical composition. But the Hubble Space Telescope data
Ferraro has shown there are dramatic differences in blue horizontal-branch (HB) and blue straggler star populations: M3 has a frequency of blue stragglers 3 times that of M13.
Data
This represents 4.5 hrs of 9 x 600s SBIG RGB filtered subs using the RCOS 16" f/8.9 (3550mm focal length) Robotic Telescope at Sierra Remote Observatories, Auberry, California and a SBIG STX16803 16MP (4096 x 4096) CCD Camera.
Processing
I calibrated and stacked in DeepSkyStacker; did L(synthetic)RGB composting, stretching, HDR, deconvolution, color calibration and noise reduction in StarTools; and final touches in PhotoShop.
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