Stars can cluster together in groups rather than be spread out like the Sun is to its neighbours.
There are two main groups of star clusters :-
Open Cluster
Globular Cluster
What is a star Cluster?
The term refers to groups of stars that are either tightly clustered together (Globular) or loosely (Open). The most well known and famous of clusters must be the Seven Sisters or Pleiades in the constellation of Taurus. They should not be considered as being unique to our galaxy, the Milky Way. A global cluster has been found in NGC 4874 Springer
What is a Globular Star Cluster?
Globular clusters tend to be old clusters of stars that can range in numbers from 10,000 to anything up to several million. The shape of Globular Clusters are roughly spherical in nature hence where its name comes from (Globe). As mentioned, they tend to be old stars, born not that long after the the beginning of the universe. Although the vast majority of Globular Clusters contain white and yellow stars, they have been a few blue stars in amongst clusters.
Globular Clusters tend to be found nearer the Galactic Centre of the galaxy whereas Open ones tend to be further out. The Pleiades Cluster is a good example of an open Cluster, they are in the opposite direction to the centre of the Galaxy, Sagittarius A*. For the opposite, Messier 80 is a Globular Cluster in the constellation of Scorpius.
Some galaxies do not have a Supermassive black hole at its heart, some will have a Globular Cluster at the heart instead.
Omega Centauri, Largest Globular Cluster
The largest Globular Cluster in the galaxy is Omega Centauri located in Centaurus galaxy. The Globular Cluster is estimated to have at least 10 millions stars of different colours and sizes. The combined mass is equivalent to four million solar masses. The picture below is taken from the Hubble space telescope. Some of the blue stars are likely to be blue stragglers, or vampire stars.
What is an Open Star Cluster?
Stars in an Open Cluster tend to be younger stars compared to Globular Clusters and they don't tend to be as tightly compact. Open Cluster stars all tend to be made of the same material and can be of different ages. At the birth of the Open Cluster, all the stars will be of the same age but they can die at different rates. All the stars aren't the same size but be varying sizes. They don't all stay clustered together as they can different away from one another.
Of the two types of cluster, these are the more common of the two types with as many as 1000 having been discovered. An Open Cluster whilst it can loose stars as they move away, it can replace the lost stars with new stars from the same material. This is something that a Globular Cluster is unable to do, that is replace a star which is lost. When a Globular Star is lost, its lost and irreplaceable thereafter.
Hyades, Local Star Cluster
The Hyades open star cluster is a local star cluster to us at around 153 light years. The cluster is located in the constellation of Taurus, the bull. The Hyades includes some of the well know Taurian stars such as Ain also known as Epsilon Tauri. Although located near Aldebaran, Aldebaran is not a member of the Hyades. Ain is of particular interest because has an orbiting exoplanet.
Age of a Cluster
You can determine the age of the star cluster by looking at the colour of the stars that exist in the cluster. All the stars should be roughly the same age. If the cluster is relatively blue then the stars are hot and young and will only last millions of years. If the cluster is yellow then the cluster will last billions of years. If the cluster is red then the cluster is old and can last trillions of years.
If the cluster is predominantly red but there are some blue stars in amongst the stars then its a good sign that there are Vampire Stars in amongst the cluster. These vampire stars are referred to as Blue Stragglers. In short, vampire stars suck material and fuel from a close star and as they feed and grow, the Vampire Star can appear blue and younger than other stars in the cluster. Ref: Science Channel
Name Type Constellation
Messier 2 (NGC 7089)Globular ClusterAquarius
Messier 72 (NGC6981)Globular ClusterAquarius
Messier 73 (NGC6994)Star Cluster (4 Star System)Aquarius
Westerlund - 1Star ClusterAra
Messier 36 (NGC1960)Open ClusterAuriga
Messier 37 (NGC2099)Open ClusterAuriga
Messier 38 (NGC1912)Open ClusterAuriga
Praesepe, the Beehive Cluster (M44, NGC2632)Open ClusterCancer
Messier 67 - King Cobra ClusterOpen ClusterCancer
Messier 3 (NGC5272) Globular Cluster Canes Venatici
Messier 41 (NGC2287) Open Cluster Canis Major
Messier 30 (NGC7099) Globular Cluster Capricornus
Westerlund - 2 Star Cluster Carina
Pincushion Cluster, Football Cluster, Wishing Well Cluster, Caldwell 91 Star Cluster Carina
NGC 3114 Open Cluster Carina
NGC 7789 Open Cluster Cassiopeia
NGC 1027 Open Cluster Cassiopeia
Owl Cluster Open Star Cluster Cassiopeia
Messier 103 (NGC581) Open Cluster Cassiopeia
Messier 52 (NGC7654) Open Cluster Cassiopeia
Omega Centauri Globular Cluster Centaurus
Pearl Cluster Cluster Centaurus
NGC 7160 (Open Galactic Cluster) Open Galactic CLuster Cepheus
Messier 53 (NGC5024) Globular Cluster Coma Berenices
Jewel Box Star Cluster Open Cluster Crux
Messier 39 (NGC7092) Open Cluster Cygnus
Cooling Tower Nebula (M29, NGC6913) Open Cluster Cygnus
NGC 7006 Globular Cluster Delphinus
NGC 1866 Globular Cluster Dorado
Tarantula Nebula (NGC2070) Globular Cluster Dorado
NGC 2158 Open Star Cluster Gemini
Messier 35 (NGC2168) Open Cluster Gemini
The Great Hercules Globular Cluster (M13, NGC6205) Globular Cluster Hercules
Messier 92 (NGC6341) Globular Cluster Hercules
Messier 68 (NGC4590) Globular Cluster Hydra
Messier 48 (NGC2548) Globular Cluster Hydra
NGC 1466 Globular Cluster Hydrus
Messier 79 (NGC1904) Globular Cluster Lepus
NGC 2419 Globular Cluster Lynx
NGC 6791 Open Cluster Lyra
Messier 56 (NGC6779) Globular Cluster Lyra
Messier 50 (NGC2323) Open Cluster Monoceros
Caldwell 50 Open Cluster Monoceros
Messier 12 (NGC6218) Globular Cluster Ophiuchus
Messier 14 (NGC6402) Globular Cluster Ophiuchus
Messier 19 (NGC6273) Globular Cluster Ophiuchus
Messier 9 (NGC6333) Globular Cluster Ophiuchus
Messier 10 (NGC6254) Globular Cluster Ophiuchus
Messier 62 (NGC6266) Globular Cluster Ophiuchus
Messier 107 (NGC6171) Globular Cluster Ophiuchus
NGC 1981 Open Cluster Orion
NGC 6752 Globular Cluster Pavo
Messier 15 (NGC7078) Globular Cluster Pegasus
Messier 34 (NGC1039) Open Cluster Perseus
NGC 884 Open Cluster Perseus
Messier 46 (NGC2437) Open Cluster Puppis
Messier 47 (NGC2422) Open Cluster Puppis
Messier 93 (NGC2447) Open Cluster Puppis
Messier 71 (NGC6838) Globular Cluster Sagitta
Messier 75 (NGC6864) Globular Cluster Sagittarius
Messier 69 (NGC6637) Globular Cluster Sagittarius
Messier 70 (NGC6681) Globular Cluster Sagittarius
Messier 54 (NGC6715) Globular Cluster Sagittarius
Messier 55 (NGC6809) Globular Cluster Sagittarius
Messier 28 (NGC6626) Globular Cluster Sagittarius
Messier 18 (NGC6613) Open Cluster Sagittarius
Messier 21 (NGC6531) Open Cluster Sagittarius
Facies, Messier 22 (NGC6656) Globular Cluster Sagittarius
Messier 23 (NGC6494) Open Cluster Sagittarius
Sagittarius Star Cloud (M24) Milky Way Patch Star Cloud with Open Cluster Sagittarius
Messier 25 Open Cluster Sagittarius
NGC 6723 Globular Cluster Sagittarius
NGC 6388 Globular Cluster Scorpius
Butterfly Cluster (M6, NGC6405) Open Cluster Scorpius
Ptolemys Cluster (M7, NGC6475) Open Cluster Scorpius
Messier 4 (NGC6121) Globular Cluster Scorpius
Messier 80 (NGC6093) Globular Cluster Scorpius
Wild Duck Cluster (M11, NGC6705) Open Cluster Scutum
Messier 26 (NGC6694) Open Cluster Scutum
Messier 5 (NGC 5904) Globular Cluster Serpens
Pleiades (M45) Open Cluster Taurus
Hyades Open Star Cluster Taurus
47 Tucanae Globular Cluster Tucana
NGC 346 Open Cluster Tucana
Winnecke 4 (M40) Star Cluster (Double Star) Ursa Major
NGC 2547 Open Cluster Vela
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