An open cluster is a type of star cluster made of tens to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and many more are thought to exist. Each one is loosely bound by mutual gravitational attraction and becomes disrupted by close encounters with other clusters and clouds of gas as they orbit the Galactic Center. This can result in a loss of cluster members through internal close encounters and a dispersion into the main body of the galaxy. Open clusters generally survive for a few hundred million years, with the most massive ones surviving for a few billion years. In contrast, the more massive globular clusters of stars exert a stronger gravitational attraction on their members, and can survive for longer. Open clusters have been found only in spiral and irregular galaxies, in which active star formation is occurring.
Star clusters are large groups of stars held together by self-gravitation. Two main types of star clusters can be distinguished. Globular clusters are tight groups of ten thousand to millions of old stars which are gravitationally bound. Open clusters are more loosely clustered groups of stars, generally containing fewer than a few hundred members, that are often very young. As they move through the galaxy, over time, open clusters become disrupted by the gravitational influence of giant molecular clouds. Even though they are no longer gravitationally bound, they will continue to move in broadly the same direction through space and are then known as stellar associations, sometimes referred to as moving groups.
Coma Berenices is an ancient asterism in the northern sky, which has been defined as one of the 88 modern constellations. It is in the direction of the fourth galactic quadrant, between Leo and Boötes, and it is visible in both hemispheres. Its name means "Berenice's Hair" in Latin and refers to Queen Berenice II of Egypt, who sacrificed her long hair as a votive offering. It was introduced to Western astronomy during the third century BC by Conon of Samos and was further corroborated as a constellation by Gerardus Mercator and Tycho Brahe. It is the only modern constellation named after a historic person.
Messier 13 or M13, is a globular cluster of several hundred thousand stars in the constellation of Hercules.
This is a list of lists, grouped by type of astronomical object.
Philibert Jacques Melotte was a British astronomer whose parents emigrated from Belgium.
Robert Julius Trumpler was a Swiss-American astronomer.
The Carina Nebula or Eta Carinae Nebula is a large, complex area of bright and dark nebulosity in the constellation Carina, located in the Carina–Sagittarius Arm of the Milky Way galaxy. The nebula is approximately 8,500 light-years (2,600 pc) from Earth.
The Antennae Galaxies are a pair of interacting galaxies in the constellation Corvus. They are currently going through a starburst phase, in which the collision of clouds of gas and dust, with entangled magnetic fields, causes rapid star formation. They were discovered by William Herschel in 1785.
NGC 6633 is a large bright open cluster in the constellation Ophiuchus. Discovered in 1745-46 by Philippe Loys de Chéseaux, it was independently rediscovered by Caroline Herschel in 1783 and included in her brother William's catalog as H VIII.72. Bright enough to be seen with the naked eye, the cluster is considered a fine object for binoculars or small telescopes.
NGC 6231 is an open cluster in the southern sky located half a degrees north of Zeta Scorpii. NGC 6231 is part of a swath of young, bluish stars in the constellation Scorpius known as the Scorpius OB1 association. The star Zeta1 is a member of this association, while its brighter apparent partner, Zeta2, is only 150 ly from Earth and so is not a member.
The Heart Nebula is an emission nebula, 7500 light years away from Earth and located in the Perseus Arm of the Galaxy in the constellation Cassiopeia. It was discovered by William Herschel on 3 November 1787. It displays glowing ionized hydrogen gas and darker dust lanes.
The Collinder catalogue is a catalogue of 471 open clusters compiled by Swedish astronomer Per Collinder. It was published in 1931 as an appendix to Collinder's paper On structural properties of open galactic clusters and their spatial distribution.
Carina OB1 is a giant OB association in the Carina Nebula, which is home to some of the most massive and luminous stars in the Milky Way Galaxy. It includes the young star clusters Collinder 228, NGC 3293, NGC 3324, IC 2581, Trumpler 14, Trumpler 15 and Trumpler 16, the last being the home of Eta Carinae. It also includes another massive and luminous star, HD 93129A. It is approximately 2,680 parsecs (8,700 ly) from Earth.
NGC 1980 is a young open cluster associated with an emission nebula in the constellation Orion. It was discovered by William Herschel on 31 January 1786. Its apparent size is 14 × 14 arc minutes and it is located around the star Iota Orionis on the southern tip of the Orion constellation.
NGC 957 is a loosely bound open cluster located in the constellation Perseus. It has an apparent magnitude of 7.6 and an approximate size of 11 arc-minutes. It is young at less than 11 million years old.
Melotte 186 is a large, loosely bound open cluster located in the constellation Ophiuchus. It has an apparent magnitude of 3.0 and an approximate size of 240 arc-minutes.
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