M 56
55 of 111

M 56

February 18, 2005
Globular Cluster M56 (NGC 6779), class X, in Lyra

Right Ascension: 19 : 16.6 (h:m) Declination: +30 : 11 (deg:m) Distance: 32.9 (kly) Visual Brightness: 8.3 (mag) Apparent Dimension: 8.8 (arc min)

Discovered by Charles Messier in 1779.

M56 is located about half-way between Beta Cygni (Albireo) and Gamma Lyrae. It is one of the less bright Messier globulars, especially lacking the bright core which most globulars have. Nevertheless it is not too difficult to resolve, even at its rather large distance. This led to its classification in concentration class X. At its distance of 32,900 light-years. its diameter of 8.8 arc minutes corresponds to a linear extension of about 85 light years. Visually, only about the inner third of this great ball, of about 3' diameter is visible. While the NGC mentions "stars of 11th to 14th magnitude", more modern measurements have shown that the brightest stars in this cluster are of about 13th magnitude, and the horizontal branch level is at magnitude 16.2 (according to the Deep Sky Field Guide to Uranometria 2000.0). Helen Sawyer Hogg gives an average magnitude of 15.31 for the 25 brightest stars, an overall spectral type of F5, and a color index of -0.04.

Globular cluster M56 was found by Harlow Shapley to be elongated with ellipticity 8 (E2) at position angle 45 deg. He found only 1 variable star in it, and even until today, only about a dozen of variables were identified in M56. This stellar swarm is approaching us at the high velocity of 145 km/sec.

M56 was one of Charles Messier's original discoveries; he saw it first on January 23, 1779 and describes it as a "nebula without stars," like most globular clusters. It was first resolved into stars by William Herschel around 1784.

This globular cluster lies in a nice low-power Milky Way field.

comments powered by Disqus