M13 Hercules Globular Cluster

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2012/04/29 - M13 is the second global cluster that I captured this night. This second light of the QSI is quite successful, 3 objects in one night. I know it's beter to focus on one object over several nights, but I'm still exploring the QSI.

Messier 13 is a globular cluster of about 300,000 stars in the constellation of Hercules. M13 was discovered by Edmond Halley in 1714, and catalogued by Charles Messier on June 1, 1764. It is located at right ascension 16h 41.7m and declination +36° 28'. With an apparent magnitude of 5.8, it is barely visible with the naked eye on a very clear night. Its diameter is about 23 arc minutes and it is readily viewable in small telescopes. Nearby is NGC 6207, a 12th magnitude edge-on galaxy that lies 28 arc minutes directly north east. A small galaxy, IC 4617, lies halfway between NGC 6207 and M13, north-northeast of the large globular cluster's center.

M13 is about 145 light-years in diameter, and it is composed of several hundred thousand stars, the brightest of which is the variable star V11 with an apparent magnitude of 11.95. M13 is 25,100 light-years away from Earth.

Object information
Name : M13 Hercules Globular Cluster
Type : Globular cluster
Constellation : Hercules
Distance : 22.200 light-year
Apparent dimensions : 20'
Apparent magnitude : 5.80

Image information
Image date : 2012/04/29
Right ascension : 16:41:34.921
Declination : 36°24' 32.27"
Focal length : 1504.85 mm
Focal ratio : f/5.92
Image resolution : 0.740 arcsec/pixel
Field of view : 43' 43.1" x 29' 9.0"
Sensor temperature : -25°C
Light frames : 14 minutes, 30 seconds total exposure time
12x 20 sec. luminace unbinned
14x 15 sec. RGB 2x2 binned
Image acquisition scripted with Nebulosity v3
Auto-guiding with PHD
Bias frames : 100x unbinned
50x 2x2 binned
Dark frames : Bap pixel map
Flat frames : no flats
Processing : PixInsight for calibration (bias frames, bad pixel map and flat frames), alignment and integration.
Adobe Photoshop CS6 for final touch.

Equipment information
Telescope : Sky-Watcher BKP250 10" 1200mm f/4.8 Newtonian
Corrector : Guan Sheng Optical 2" coma corrector and field flattener
Focuser : Moonlite CR newtonian focuser with DC motor and USBnFocus adapter
Mount : Sky-Watcher NEQ6-Pro german equatorial mount controlled with EQMOD via HiTec Astro EQDir
Camera : QSI 683wsg-8 cooled CCD camera with Kodak KAF-8300 sensor and Off Axis Guide (OAG) port
Guidecamera : Starlight Xpress Lodestar autoguider
Filters : Astrodon Tru-Balance E-Series LRGB & Astrodon 3nm H-α, 3nm O-III, 3nm S-II and 3nm N-II
Observatory site : Etten-Leur, The Netherlands