Star cluster
Globular clusters are tight groups of ten thousand to millions of old stars which are gravitationally bound.
As they move through the galaxy, over time, open clusters become disrupted by the gravitational influence of giant molecular clouds.
Unlike the spherically distributed globulars, they are confined to the galactic plane, and are almost always found within spiral arms.
[3] Establishing precise distances to open clusters enables the calibration of the period-luminosity relationship shown by Cepheids variable stars, which are then used as standard candles.
Cepheids are luminous and can be used to establish both the distances to remote galaxies and the expansion rate of the Universe (Hubble constant).
[4][5] Embedded clusters are groups of very young stars that are partially or fully encased in interstellar dust or gas which is often impervious to optical observations.
[6] The embedded cluster phase may last for several million years, after which gas in the cloud is depleted by star formation or dispersed through radiation pressure, stellar winds and outflows, or supernova explosions.
With the loss of mass in the cloud, the energy of the system is altered, often leading to the disruption of a star cluster.
However, nearly all freely floating stars, including the Sun,[8] were originally born into embedded clusters that disintegrated.
[7] Globular clusters are roughly spherical groupings of from 10 thousand to several million stars packed into regions of from 10 to 30 light-years across.
In 1917, the astronomer Harlow Shapley made the first respectable estimate of the Sun's distance from the Galactic Center, based on the distribution of globular clusters.
However, greatly improved distance measurements to globular clusters using the Hipparcos satellite and increasingly accurate measurements of the Hubble constant resolved the paradox, giving an age for the universe of about 13 billion years and an age for the oldest stars of a few hundred million years less.
They are characterized by their large size compared to globular clusters and a ringlike distribution around the centres of their host galaxies.
These clusters, especially the young ones can explain the star formation process that might have happened in our Milky Way Galaxy.
Nearly all stars in the Galactic field, including the Sun, were initially born in regions with embedded clusters that disintegrated.
This means that properties of stars and planetary systems may have been affected by early clustered environments.
In 1979, the International Astronomical Union's 17th general assembly recommended that newly discovered star clusters, open or globular, within the Galaxy have designations following the convention "Chhmm±ddd", always beginning with the prefix C, where h, m, and d represent the approximate coordinates of the cluster centre in hours and minutes of right ascension, and degrees of declination, respectively, with leading zeros.
