M12: A globular cluster is a group of ancient stars (M12 is thought to be about 12.7 billion years old; by comparison, our sun is about 4.6 billion years old; our galaxy is about 13.5 billion years old, and the universe is thought to be 13.8 billion years old), gravitationally bound to each other, orbiting the core of its associated galaxy.

M12 is somewhat less densely packed with stars than most globular clusters; M12 was once thought to be a tightly concentrated open cluster, but now is known to be a globular cluster. M12 has fewer low-mass stars than expected; astronomers suspect that gravity has ripped many low-mass stars from M12 as the cluster passed through denser regions of the Milky Way during its orbit around the galaxy’s center. M12 is thought to have lost up to one million stars this way; it has about 250,000 stars remaining (for comparison, there are estimated to be no more than 2,000 stars within 50 light years of earth, which is a considerably larger bubble than the size of M12).

M12 is about 23,000 light years from Earth, and is about one-fifth of the angular size of the full moon when viewed from very dark skies; it is roughly 75 light years across. It shines at magnitude 7.7 (not quite visible with the naked eye even in the darkest skies, but easily seen with binoculars).

Technical Information:

LRGB: 210:60:60:117 (about 7-1/2 hours of light-frame exposures); luminance layer consists of 36 five-minute images and 30 one-minute images; RG channels consist of the combination five-minute images, while B was a group of 6.5-minute images.

Equipment: RC Optical Systems 14.5 inch Ritchey-Chretien carbon fiber truss telescope, with ion-milled optics and RCOS field flattener, at about f/9, and an SBIG STX-16803 with internal filter wheel (SBIG filter set), guided by an SBIG AO-X, all riding on a Bisque Paramount ME German Equatorial Mount.

Image Acquisition/Camera Control: Maxim DL, controlled with ACP Expert/Scheduler, working in concert with TheSky X.

Processing: All images calibrated (darks, bias and sky flats), aligned, and combined in Pixinsight. Some finish work (background neutralization, color calibration, gradient removal, HDR Multiscale Transform (lessening the dynamic range), Multiscale Linear Transform, done in Pixinsight; some finish work (Neat Image noise reduction, LRGB combination, contrast and saturation adjustment) was done in Photoshop CC.

Location: Data acquired remotely from Sierra Remote Observatories, Auberry, California, USA.

Date: Images taken on five consecutive nights in mid-May of 2021. Image posted June 13, 2021.

Date: Image scale of full-resolution image: 0.56 arcseconds per pixel.

Seeing: Generally good, with calibrated luminance images varying from 1.7 to 2.4 arcsecond FWHM

CCD Chip temperature: -25C

Copyright 2021 Mark de Regt

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