The Great Globular Cluster in Hercules

The Great Globular Cluster in Hercules — also known as M13 in the Messier catalogue or NGC 6205 in the New General Catalogue — is one of the best examples of a globular star cluster to observe with a small telescope in the Northern Hemisphere.

M13 contains several hundred thousand stars and is around 6,800 parsecs (approximately 22,000 light years) from Earth orbiting the Milky Way outside of the galactic disk. The cluster is around 44 parsecs (145 light years) in diameter (see Astronomical Distance Measurements).

M13 Great Globular Cluster in Hercules — Hubble Space Telescope image of the centre of the Great Globular Star Cluster in Hercules. Credits: NASA, ESA, and the Hubble Heritage Team (STScI/AURA); Acknowledgment: C. Bailyn (Yale University), W. Lewin (Massachusetts Institute of Technology), A. Sarajedini (University of Florida), and W. van Altena (Yale University) source: https://www.nasa.gov/feature/goddard/2017/messier-13-the-hercules-cluster

M13 was discovered by Edmond Halley in 1714 and added by Charles Messier to his catalogue in 1764 so he wouldn’t mistake it for a comet, as individual stars in the cluster were not resolvable by telescopes until 1779.

The brightest stars in the cluster are older red giant stars (see Types of Stars), some of which are 12 to 13 billion years old – almost as old as the universe. Younger stars include “blue stragglers”, which are formed from collisions between the stars.

Location

M13 has an apparent visual magnitude of 5.8 — just visible to the unaided eye in good viewing conditions — and can be located about two thirds of the way between Zeta and Eta Herculis in the constellation of Hercules.

The equatorial coordinates of M13 are: Right Ascension: 16h 41m 41.24s, Declination: +36° 27′ 35.5″.

To find the current position of M13 in the sky from your location, visit our Night Sky Simulator.

Astronomy, Cosmology, Space and Astrophysics