M92: A globular cluster is a group of ancient stars (M92 is thought to be 13.8 billion years old, gravitationally bound into a spherical shape; 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 only slightly older than M92), orbiting the core of its associated galaxy.

M92 is about 26,700 light years from Earth, and is about one-half of the angular size of the full moon when viewed from very dark skies. It is roughly 108 light years across. It shines at magnitude 6.4 (barely visible, in very dark skies, to the naked eye, but easily seen with binoculars). It has a mass equal to about 330,000 times that of our sun (for comparison, there are estimated to be no more than 2,000 stars within 50 light years of earth, which is a similar-sized bubble); it would be a very bright "night sky" on a planet in the midst of that cluster!

Because all the stars in a globular cluster are essentially the same distance from us (relative to the absolute distance from us), it is interesting to create a Hertzsprung-Russell diagram ("HR Diagram") of the members of the cluster. To learn about HR Diagrams, click here. I have done just that for this ancient cluster; those charts are here (absolute magnitude) and here (apparent magnitude). In addition to the interesting science, this is an interesting way to validate the colors the software created for the cluster from my data.

I last imaged this cluster 20 years earlier. To see what a combination of better equipment, better skies, better software, and better skills does, click here

Technical Information:

L:R:G:B: 266:140:135:196 (a total of over 12 hours of light-frame exposure time); here's a chart showing the various subexposures I used in the image:
Luminance: 49 five-minute and 31 one-minute
Red: 24 five-minute and 20 one-minute
Green: 23 five-minute and 20 one-minute
Blue: 27 six-and-one-half minute and 20 one-minute

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 STX guider, 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, NoixeXTerminator, BlurXTerminator, 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 during many nights in late June and July of 2025. Image posted October 26, 2025.

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

Seeing: Generally good

CCD Chip temperature: -25C

Copyright 2025 Mark de Regt