Globular Cluster M15


In November 2018, a few moonless nights with low humidity and calm winds allowed some relative deep-sky imaging.  The C11-Edge telescope was mounted on my MyT Paramount in my suburban backyard, with estimated naked-eye limiting magnitude about 4. A Celestron 0.7x focal reducer produced a focal length about 1960mm.  A ZWO 1600 monochrome CMOS camera was used, resulting in 0.41 arcsec per pixel resolution. A luminance filter was used in the 15second exposures.  Dark frames and a twilight flat were used to calibrate the image.  The ZWO gain was set at 50, giving about 2.8 electrons/ADU. This camera uses a 12-bit digitizer.


The first image is a cropped view of most of the cluster, with DEC increasing in the vertical and RA increasing to the left.  The second image is a close-up of the central core, with less image stretching.  The measured stellar resolution in both images is 5.2 pixels, or 2.1 arcseconds.  The best 149 images (out of 200 images) were aligned and stacked, providing 37 minutes total exposure.





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