Hercules Globular Cluster

Hercules Globular Cluster is Messier 13 or designated NGC 6205, a globular cluster of several hundred thousand stars in the Hercules constellation. For many stargazers, M13 is the finest globular cluster in the northern half of the heavens. It is in a star pattern Keystone– an asymmetrical square in the constellation Hercules that is in between Vega and Arcturus, the two brightest stars of northern spring and summer. With over 100,000 stars whirl within the globular cluster M13, it appears like a shiny flake sparkling in a snow globe and is one of the brightest star clusters visible from the Northern Hemisphere.

Located 25,000 light-years from Earth, an apparent magnitude of 5.8, and about 145 light-years in diameter, this glittering metropolis of stars in the constellation Hercules has drawn the eyes of many astronomers and spectators since its discovery in 1714. You can spot it most easily with a pair of binoculars, especially in July.

An English astronomer Edmond Halley discovered M13 in 1714, and Charles Messier it to his catalog in 1764 as he was convinced that the nebulous object did not contain any stars. The M13 is so compacted that its individual stars were not resolved until 1779. Near its core, all the stars’ density is about a hundred times greater than that of the sun’s neighborhood. These stars are so crowded that they attract each other and even form a new star- “blue stragglers” that appear to be younger than the other stars in their immediate vicinity and are of great scientific interest to astronomers.

Halley described the cluster as a little patch that shows itself to the naked eye when the sky is serene, and the Moon is absent. In 1974, Messier 13 was the target of a symbolic Arecibo radio telescope message communicating humanity’s existence to possible extraterrestrial intelligence. However, according to several recent studies, in the dense environments of globular clusters, planets are scarce to exist.

Messier 13 was also used in a novel written in 1959 entitled The Sirens of Titan written by Kurt Vonnegut. And to quote a particular line from that novel, Vonnegut wrote: “Every passing hour brings the Solar System forty-three thousand miles closer to Globular Cluster M13 in Hercules — and still there are some misfits who insist that there is no such thing as progress.”

Visibility of M13

a wider surrounding view of the Messier 13

Although it’s not the easiest to be seen in the night sky, using a telescope at mid-northern latitudes, the M13 cluster can be seen for at least part of the night all year round. A portion of it is visible in the night in April and all night long in May, June, and July. In August and September, the Hercules cluster is still very much a night owl, staying up till after midnight. When you see M13 or other globular, you see stars about 12 to 13 billion years old, almost the same age as the universe.

About one-third of the way from Vega to Arcturus, locate the four modestly bright stars forming the Keystone of Hercules. On the Keystone’s Arcturus side, M13 is found between the stars Eta Herculis and Zeta Herculis.

Although telescopes with great light-gathering capability can fully resolve the stars of the Cluster, M13 can still be seen by the naked eye given good circumstances. With a low-power telescope, Messier 13 looks like a comet or fuzzy patch. The cluster is visible throughout the year from latitudes greater than 36 degrees north, with the longest visibility during Northern Hemisphere spring and summer.

A typical binocular field measures 5 to 6 degrees in diameter, and the Hercules cluster can be spotted about 2.5 degrees south of Eta Herculis. With the naked eyes on a clear night, one can perceive the Hercules cluster as a faint and possibly fuzzy light point. Binoculars are also helpful to see this fuzzy globular much easier.

Generally, globular clusters move around the Milky Way outside the galactic disk at tens of thousands of light-years away. Contrary, the relatively nearby Pleiades and Hyades open star clusters exist within the galactic disk, usually harbor a few hundred to a thousand stars. Telescopes with large aperture can let you see much clearer details of the globular cluster however, with a low-power telescope, the Hercules Globular cluster looks hazy. It looks like a comet in appearance.

In traditional binoculars, the Hercules Globular Cluster appears as a round patch of light. At least four inches of telescope aperture will allow resolving the stars in M13’s outer extents as small pinpoints of light. However, only larger telescopes allow resolving stars further into the center of the cluster.