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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