Geography - Our Universe
The study of universe is known as Cosmology.
Cosmo (universe) + Logos (science)
Definition: The universe is the name given to the totality of existence of everything. It includes all physical matter, visible and latent energy, the planets, stars, galaxies and the contents of intergalactic space. The universe or the cosmos as perceived today, consists of millions of galaxies.
A galaxy is a huge congregation of stars which are held together by the force of gravity. Most of the galaxies appear to be scattered in the space in a random manner but these are many others which remain clustered into groups.
Milky Way or Akash Ganga
Our own galaxy called the Milky Way or Akash Ganga, which appears as a river of bright light flowing through the sky, belongs to a cluster of some 24 galaxies called the ‘Local Group’.
The Big Bang theory is the prevailing cosmological model for the universe from the earliest known period through its subsequent large scale evolution. The model describes how the universe expanded from a very high density and high temperature state.
Stars are self-luminous bodies situated at enormous distant from the solar system. The distant of the stars are expressed in light years. The nearest star to the earth is sun, which is the source of most of the energy on earth.
Different kinds of stars are following:
Star Clusters: Star Clusters or Star Clouds are group of stars.
Two types of star cluster can be distinguished:-
Stellar Association: it is a loose group of open clusters of stars. That are moving in the same direction but these are not gravitationally bounded to each other. The most highly visible type of stellar association is dominated by young massive stars and is called an OB association.
The Big Dipper: The Big Dipper, also known as the Plough or the Saptarishi in India , is a group of seven stars distinctly visible near the North Pole star called the Polaris.
Ursa Major: these are also known as the Great Bear, is a constellation of stars near the North Celestial Pole. It is visible throughout the year in most of the northern hemisphere. Big Dipper or Saptarishi is a part of Ursa Major.
Ursa Minor: Ursa Minor also known as Little Bear, Ursa Minor is a constellation in the northern sky. Like the Great Bear, the tail of the Little Bear may also be seen as the handles of a lade, hence the name little dipper.