M13 - Hercules Globular Cluster

M13 - Hercules Globular Cluster: This globular cluster in Hercules is one of the most prominent in the northern hemisphere. On dark summer nights it can be seen with the naked eye.

The name "globular" cluster, coined by William Hershel, is very descriptive of their appearance - a glob of stars. There are fewer than 200 globular clusters known around the Milky Way, and unless you are familiar with specific ones, they all look very similar. These clusters condensed while the Milky Way was still forming, and reside in a spherical halo around the disk. Unlike objects in the disk, which have a mostly orderly rotation about the galactic center, the orbits of globular clusters are random. It was the three dimensional distribution of globular clusters that Harlow Shapely used to find the center of the Milky Way. All large galaxies are observed to have globular clusters in a halo. Globular clusters are ancient. Generally comprising what are called Population II stars (old ones with fewer heavy elements), there are no longer any luminous, blue, main sequence stars, and the remaining distribution of stars is noticeably redder than that found in open clusters in the spiral arms. Lots more information can be found here: http://en.wikipedia.org/wiki/Globular_cluster

Messier: 13
Right Ascension: 16h 42m
Declination: 36° 27.6'
Apparent Magnitude: 5.8

Date: May 2013
Equipment:
Telescope: Meade 16" Schmidt Cassegrain with f6.3 reducer
Camera: SBIG ST-10XE
Guiding: Meade 5" refractor/DSI Pro/PHD
Exposure: L: 18x3m binned 1x1; R: 5x3m; G: 5x3m; B: 4x3m binned 2x2
Processing Notes: Captured in CCDSoft; Reduced and aligned in CCDStack; Combined in Sigma; RGB was combined in CCDStack, but after import to Photoshop, color balance was adjusted by inspection. Luminosity file was noise reduced and sharpened. Color was added as another layer. One region had an additional artificial flat field to correct for an imperfect flat file. Several stars that were over-saturated were not repaired.
Scale: ~.54"/pixel

Additional Comments: Although the original data was collected in May 2013, final processing was not completed until March 2014. An image of M13 taken at the FLC Observatory in 2008 can be found here: http://www.fortlewis.edu/observatory/image_detail.asp?ID=62

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