Star Clusters
A star cluster is an area of greatly increased density of stars compared to the surrounding area of a galaxy.
A globular cluster is a special type of star cluster consisting of a large number of stars arranged in a spherical distribution around a common centroid.
These clusters are held together by gravity and are usually found outside of a galaxy's plane, mostly in the halo region around spiral galaxies.
Globular clusters have some distinctive features:
1. Compact Spherical Shape
The stars in a globular cluster are densely packed, forming a nearly spherical structure. The stars are relatively close together compared to the average distances between stars in a galaxy.
2. High Star Density
Globular clusters can contain hundreds of thousands or even millions of stars concentrated in a relatively small volume. This high star density is one of the reasons globular clusters can appear so striking and impressive in the sky.
3. Old Stars
Most stars in a globular cluster are very old. They are among the oldest stars in the universe and were often formed at a time when galaxies were still forming.
4. Small amounts of interstellar gas and dust
Unlike younger star clusters, globular clusters contain only small amounts of interstellar gas and dust. This is because, over time, these materials have been consumed by the stars or ejected from the cluster.
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Asterisms
Asterisms are conspicuous stellar constellations that are not considered constellations in their own right. They are a superset of the 88 formally defined constellations.
