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M3 - Globular Cluster in Canes Venatici M3 - Globular Cluster in Canes Venatici ©2015 Frederick Steiling
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Target Information
Main Target Designations M3 / NGC5272
RA Center 13h 42m 10.800s
DEC Center +28° 22' 47.66"
Rotation -0.658°
One-shot color 15x480" (ISO1600)
One-shot color [HDR] 8x120" (ISO1600)
Total Integration 2hrs 16min
Date(s) of acquisition 28Mar2015
Location Whiteside, MO
Imager Olympus E-P5
Telescope/Lens Orion 8" f/3.9 Astrograph
Mount Celestron CGEM
Guiding Apparatus Orion ST80 (piggyback)
Guiding Camera Orion SSAG
Coma Corrector Baader MPCC Mark III
Collimator Orion LaserMate
Focusing Bahtinov mask
Acquisition Manual (remote shutter)
Guiding PHD2
Processing PixInsight 1.8

At a "paltry" distance of only 36,000 light years sits one of the more unique types of objects we'll find out there.  Globular clusters, as their name indicates, are densely packed spherical collections of stars.  In this photo, M3 (Messier 3) proudly displays its pack of 500,000 stars, a handful of which are real treats for research.  M3 is known for its unusually high number of variable stars -- stars which vary to and fro in brightness.  274 of these variable stars have been identified in this cluster, more than have been found in any other cluster to-date.  For this reason, M3 is not only considered one of the most beautiful globular clusters in our sky, it is also one of the most intriguing as well.

This relatively quick 2 hour integration was done as a test of a composition method called HDR.  High-dynamic-range compositions can be done with objects that have very high brightness in parts, but also have important dim details.  I first used 8 minute subexposures (my current baseline for deep space photos) to expose the entire cluster, including its outer extents.  However, in doing so and because the core of the cluster is so bright, the core was oversaturated and clipped, leaving poor full-white data in the middle of the frame.  To counter this, I next used 2 minute subexposures to get better detail on the core (though the outer reaches were less defined).  Using HDR composition, I was able to extend the range of the 8' image and replace details of the oversaturated core with the details found in the 2' composition.  The result is better detail across the entire cluster, from the edges to the middle.

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