M3: A globular cluster is a group of ancient stars (M3 is thought to be about 11.4 billion years old--although some estimate the age as 8 billion years; 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.

M3 is about 34,000 light years from Earth, and is about two-thirds the angular size of the full moon when viewed from very dark skies; it is roughly 220 light years across. It shines at magnitude 6.2 (which might be visible to the naked eye in absolutely dark skies). It has a mass equal to about 800,000 times that of our sun, and contains as many as 500,000 stars (for comparison, there are estimated to be no more than 14,000 stars within 100 light years of earth, which is a bubble about that same size). It has an unusual concentration of blue-straggler stars (stars that are much less old than the other stars in the cluster, probably formed from collisions or other interactions between stars in the cluster), and its core is unusually dense.

Technical Information:

LRGB: 179:105:105:117; luminance layer consists of 26 five-minute images and 49 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. Color combine in Pixinsight. Some finish work (background neutralization, color calibration, gradient removal, deconvolution, Multiscale Linear Transform, lessening the dynamic range) 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 many nights in May 2020. Image posted June 9, 2020.

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

Seeing: Generally excellent, with uncalibrated luminance images varying from 1.4 to 2.0 arcsecond FWHM

CCD Chip temperature: -25C

Copyright 2020 Mark de Regt

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