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 milky way is made up of over a hundred billion sparkling stars, which through quit distant from one another, seem from the earth as having been placed close together.
- Milky Way galaxy was formed 5 billion years after the Big Bang.
- It is a spiral galaxy that contains 100-400 billion stars and an estimated 50 billion planets, 500 million of which could be located in the habitable zone of their parent star.
- Latest known galaxy is the Dwarf Galaxy.
- Andromeda is our nearest galaxy.
- The sun is one of the stars in the Milky Way galaxy.
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.
- The Big Bang theory is about how the universe started, and then made the stars and the galaxies….
- The universe began very hot, small and dense with no stars atoms, forms or structure.
- Then about 13.8 billion years ago space expanded very quickly. This started the formation of atom, which eventually led to the formation of stars and galaxies.
- In 1927, Georges Lemaitre was first noted that an expanding universe could be traced back in time to an originating single point. The universe is still expanding today, but getting colder as well.
- Fred Hoyle called the theory “The Big Bang” on his radio show.
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:
- Fixed stars: These are stars which do not appear after their relative position in the sky. These are also called the dog stars.
- Binary stars: These are group of two stars revolving round each other under mutual gravitational attraction.
- Temporary stars: Temporary stars are those which suddenly flare up to greatly increased brightness and fade after a short time.
- Variable stars: Variable stars are stars the brightness of which varies from time to time.
- Dwarf: These are small stars; the brightest among these are blue dwarf and the dimmest are red dwarf.
- Novae: Novae are stars which seem to appears out of nowhere and later disappear. Ancient Chinese Astronomers called them guest stars. They are also known as New (Nova) stars.
- Red Giant: Red Giants are stars which have consumed about 10% of their hydrogen on account of which they appears reddish.
Two types of star cluster can be distinguished:-
- Globular clusters: These are tight groups of hundreds of thousands of very cold stars which are gravitationally bounded.
- Open clusters: these are more loosely clustered group of stars, generally contain fewer then a few hundred members, are often very young.
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.