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Catalogue and alternative designations M 55, NGC 6809 


Type Globular Cluster 
Position 19 40 00, -30 57 53
Constellation Sagittarius
Camera and Telescope STXL6303 and 36.8cm RCOS Ritchey Chretien
Focal Ratio F9
Exposure Details A LRGB shot with L=R=B=50 minutes. A synthetic green channel was created by combining the red and blue. All exposures used Astrodon filters and were unbinned.


Description M 55 is one of the many globular clusters in Sagittarius but perhaps less well known than some of the others. The apparent magnitude is 6.3 and the dimensions are 19 arcminutes. The distance is 17,600 light years.  M 55 is one of the less condensed globulars having a concentration class of 11. It is thus easily resolved into stars with relatively small telescopes.