Globular star clusters are a symmetrical collection of ancient stars (up to a million such stars). Recent estimates indicate that about 150 globulars exist in the Milky Way with only three being readily visible to the naked eye (the Andromeda Galaxy has been estimated to contain approximately 500 globular clusters). Since most of the globular clusters are more common in the southern hemisphere, scientists have deduced that our sun must lie away from the galactic core of the Milky Way. One of the most beautiful such globular clusters is M13 in Hercules.

Note: This impressive cluster in Hercules was first observed and described by Johann Elert Bode (1777) and later catalogued by Charles Messier (1781). It is believed to be comprised of a few hundred thousand stars and has been measured to lie 26,700 light-years away and with an apparent diameter of approximately 109 light-years. In spite of being an impressive globular cluster by its own right, it takes a backseat to the Great Cluster in Hercules (M13) which lies to the northeast and which is both larger in apparent diameter and slightly brighter.

As with all globular clusters, M92 in Hercules is best observed using narrow-field high-power views where, for example, the white and hot member stars provide a stunning view and similar to a large collection of diamonds against the background sky. Owing to its naked eye visibility under favourable skies, the cluster can be easily located lying between ι- and η-Her and is best observed during late spring and early summer when it is directly overhead around midnight. A few degrees to the northeast of M92 lies the stunning globular cluster within Hercules known as M13 (NGC 6205).

Note: For an excellent article on globular clusters, see S&T (Mar/2006: 30-36) as well as the article dedicated to M13 in Astronomy Magazine (May/2007: 64-67).