A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of member stars, all orbiting in a stable, compact formation. Globular clusters are similar in form to dwarf spheroidal galaxies, and the distinction between the two is not always clear. Their name is derived from Latin globulus. Globular clusters are occasionally known simply as "globulars".
A blue straggler is a type of star that is more luminous and bluer than expected. Typically identified in a stellar cluster, they have a higher effective temperature than the main sequence turnoff point for the cluster, where ordinary stars begin to evolve towards the red giant branch. Blue stragglers were first discovered by Allan Sandage in 1953 while performing photometry of the stars in the globular cluster M3.
NGC 6397 is a globular cluster in the constellation Ara that was discovered by French astronomer Nicolas-Louis de Lacaille in 1752. It is located about 7,800 light-years from Earth, making it one of the two nearest globular clusters to Earth. The cluster contains around 400,000 stars, and can be seen with the naked eye under good observing conditions.
Messier 15 or M15 is a globular cluster in the constellation Pegasus. It was discovered by Jean-Dominique Maraldi in 1746 and included in Charles Messier's catalogue of comet-like objects in 1764. At an estimated 12.5±1.3 billion years old, it is one of the oldest known globular clusters.
Messier 53 is a globular cluster in the Coma Berenices constellation. It was discovered by Johann Elert Bode in 1775. M53 is one of the more outlying globular clusters, being about 60,000 light-years (18.4 kpc) light-years away from the Galactic Center, and almost the same distance from the Solar System. The cluster has a core radius (rc) of 2.18 pc, a half-light radius (rh) of 5.84 pc, and a tidal radius (rtr) of 239.9 pc.
Messier 62 or M62, also known as NGC 6266 or the Flickering Globular Cluster, is a globular cluster of stars in the south of the equatorial constellation of Ophiuchus. It was discovered in 1771 by Charles Messier, then added to his catalogue eight years later.
Messier 70 or M70, also known as NGC 6681, is a globular cluster of stars to be found in the south of Sagittarius. It was discovered by Charles Messier in 1780. The famous comet Hale–Bopp was discovered near this cluster in 1995.
47 Tucanae or 47 Tuc is a globular cluster located in the constellation Tucana. It is about 4.45 ± 0.01 kpc (15,000 ± 33 ly) from Earth, and 120 light years in diameter. 47 Tuc can be seen with the naked eye, with an apparent magnitude of 4.1. It appears about 44 arcminutes across including its far outreaches. Due to its far southern location, 18° from the south celestial pole, it was not catalogued by European astronomers until the 1750s, when the cluster was first identified by Nicolas-Louis de Lacaille from South Africa.
NGC 1818 is a young globular cluster in the north-west part of the Large Magellanic Cloud, about 3.2 kpc from the center. It was discovered by Scottish astronomer James Dunlop in 1826, and has since been well studied.
NGC 3201 is a low galactic latitude globular cluster in the southern constellation of Vela. It has a very low central concentration of stars. This cluster was discovered by James Dunlop on May 28, 1826 and listed in his 1827 catalogue. He described it as "a pretty large pretty bright round nebula, 4′ or 5′ diameter, very gradually condensed towards the centre, easily resolved into stars; the figure is rather irregular, and the stars are considerably scattered on the south".
NGC 5986 is a globular cluster of stars in the southern constellation of Lupus, located at a distance of approximately 34 kilolight-years from the Sun. It was discovered by Scottish astronomer James Dunlop on May 10, 1826. John L. E. Dreyer described it as, "a remarkable object, a globular cluster, very bright, large, round, very gradually brighter middle, stars of 13th to 15th magnitude". Its prograde–retrograde orbit through the Milky Way galaxy is considered irregular and highly eccentric. It has a mean heliocentric radial velocity of +100 km/s. The galacto-centric distance is 17 kly (5.2 kpc), which puts it in the galaxy's inner halo.
NGC 6723 is a globular cluster in the constellation Sagittarius. Its magnitude is given as between 6 and 6.8, and its diameter is between 7 and 11 arcminutes. It is a class VII cluster with stars of magnitude 14 and dimmer. It is near the border of Sagittarius and Corona Australis.
NGC 6934 is a globular cluster of stars in the northern constellation of Delphinus, about 52 kilolight-years distant from the Sun. It was discovered by the German-born astronomer William Herschel on 24 September 1785. The cluster is following a highly eccentric orbit through the Milky Way along an orbital plane that is inclined by 73° to the galactic plane. It may share a common dynamic origin with NGC 5466. As of 2018, it has been poorly studied.
NGC 2808 is a globular cluster in the constellation Carina. The cluster currently belongs to the Milky Way, although it was likely stolen from a dwarf galaxy that collided with the Milky Way. NGC 2808 is one of our home galaxy's most massive clusters, containing more than a million stars. It is estimated to be 12.5-billion years old.
NGC 1851 is a relatively massive globular cluster located in the southern constellation of Columba. Astronomer John Dreyer described it as not very bright but very large, round, well resolved, and clearly consisting of stars. It is located 39.5 kilolight-years from the Sun, and 54.1 kilolight-years from the Galactic Center. The cluster is following a highly eccentric orbit through the galaxy, with an eccentricity of about 0.7.
NGC 1261 is a globular cluster of stars in the southern constellation of Horologium, first discovered by Scottish astronomer James Dunlop in 1826. The cluster is located at a distance of 53 kilolight-years from the Sun, and 59 kilolight-years from the Galactic Center. It is about 10.24 billion years old with 341,000 times the mass of the Sun. The cluster does not display the normal indications of core collapse, but evidence suggests it may have instead passed through a post core-collapse bounce state within the past two billion years. The central luminosity density is 2.22 L☉·pc−3, which is low for a globular cluster. Despite this, it has a Shapley–Sawyer Concentration Class of II, indicating a dense central concentration.
NGC 6352 is a globular cluster of stars in the southern constellation of Ara, located approximately 18.3 kly from the Sun. It was discovered by Scottish astronomer James Dunlop on May 14, 1826. The cluster has a Shapley–Sawyer Concentration Class of XI:. A telescope with a 15 cm (5.9 in) aperture is required to resolve the stars within this loose cluster.
NGC 6541 is a globular cluster in the southern constellation of Corona Australis. It is estimated to be around 14 billion years old.
NGC 121 is a globular cluster of stars in the southern constellation of Tucana. It is the oldest globular cluster in the Small Magellanic Cloud (SMC), which is a dwarf satellite galaxy of the Milky Way. This cluster was first discovered by English astronomer John Herschel on September 20, 1835. The compiler of the New General Catalogue, Danish astronomer John Louis Emil Dreyer, described this object as "pretty bright, pretty small, little extended, very gradually brighter middle". The cluster is located at a distance of around 200,000 light-years (60 kpc) from the Sun.
NGC 6441, sometimes also known as the Silver Nugget Cluster, is a globular cluster in the southern constellation of Scorpius. It was discovered by the Scottish astronomer James Dunlop on May 13, 1826, who described it as "a small, well-defined rather bright nebula, about 20″ in diameter". The cluster is located 5 arc minutes east-northeast of the star G Scorpii, and is some 43,000 light-years from the Sun.
