ABSTRACT
Galaxies are gravitationally bound systems that consist of a huge number of stars. The number of stars in a galaxy vary over a wide range, roughly 107
to 1014. For example, the Milky Way galaxy contains more than 200 billion stars. There are at least 100 billion galaxies in the Universe. The galaxies themselves group together to form larger structures called groups or clusters of galaxies. The largest structures seen in the Universe are called superclusters, which contain a large number of clusters. The scale of the largest supercluster is found to be about 100 Mpc. For comparison, the size of the observable Universe is a few Gpc.
