M56


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M56: This relatively unremarkable globular cluster in the constellation Lyra, is not often imaged. As with all globular clusters, it formed around the same time as the Milky Way galaxy, and comprises very old stars. This cluster is approximately 30,000 light years away.

Messier: 56
NGC: 6779
Other Catalogs: GCI 110
Right Ascension: 19h 16.6m
Declination: 30° 11'
Apparent Magnitude: 8.3

Date: September 2010
Equipment:
Telescope: Meade 16" Schmidt Cassegrain with f6.3 reducer (used at ~ f6.1)
Camera: SBIG ST-10XE
Guiding: AO-8

Exposure: L: 31x1 minutes binned 1x1
RGB: 4x5 minutes binned 2x2
The camera was at -30°

Processing Notes: Data acquisition with CCDSoft. Reduced and aligned in CCDStack. Subs combined in Sigma Combine. Arcsine stretch import of L into Photoshop. Adjusted curves and levels, reduced noise and slight Gaussian blur of the dim areas, and applied an unsharp mask. RGB combined in AstroArt at 1:1.03:1.65 ratio. Imported TIFF into Photoshop, adjusted curves and levels, and reduced noise of dimmer areas. Slight Gaussian blur. L was combined with RGB using three layers: Luminance on the bottom; RGB as a multiply(30%) layer; and RGB as a color layer on top. Final curve tweak on the flattened image in Photoshop.
Scale: 0.52"/pixel on highest resolution

Links to images of this object on other sites:
http://en.wikipedia.org/wiki/File:Messier_56_Hubble_WikiSky.jpg
http://www.caelumobservatory.com/gallery/m56.shtml

Additional Comments: M56 was somewhat a target of opportunity. Because it is a much less impressive globular cluster than many others that are visible, it is often overlooked. This time it's proximity to the nearby M57 ring nebula worked in it's favor to attract attention. The size is well matched to the combination of focal length and camera sensor size.

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

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