Globular cluster Messier 30, at about 26,000 light years distance and 90 light years across, appears to us under an angular diameter of around 12.0 arc minutes.  It is fairly dense (as its concentration class V indicates), and a fine visual object in even small telescopes.  Its brightest red giant stars are of apparent visual magnitude 12.1, its horizontal branch giants shine at magnitude 15.1.  The core of M 30 exhibits an extremely dense stellar population and has undergone a collapse, similar to at least 20 other of the 150 globulars in the Milky Way Galaxy, including M 15, M 70 and possibly M 62.  Consequently, M 30's core is very small in extension, only 7.2 arc seconds, corresponding to a linear diameter of 0.9 light years and its half-mass radius is 1.15 arc min (8.7 light years).  Thus, half of this cluster's mass is concentrated in a spherical volume of a radius equal to the distance of Sirius from us, or 17.4 light years diameter.

Click here or on the image for a higher resolution version.  The field of view is  37 x 25 arcminutes with north towards the upper left (300°).