• It is all of time and space and its contents. It includes planets, stars, galaxies, the contents of intergalactic space, the smallest subatomic particles, and all matter and energy.
  • The study of universe is called as Cosmology.
  • The age of universe is approximately 13.8 billion years (13.8 x 109 years).

  • The observable universe is a spherical volume of space. The observable universe is about 91 billion light years in diameter.
    • Earth was the center of the Universe and the Sun, the Moon, and the other planets are orbited the Earth. – Aristotle and Claudius Ptolemy
    • Sun was the center of the Universe. – Aristarchus, Nicholas Copernicus and Galileo

    • Johannes Kepler stated that the sun is the center of solar system and not the universe.
    • In 1924, the existence of galaxies was fist demonstrated by Edwin Hubble.

    Evolution of Universe

    Big Bang Theory

    • This theory was proposed by Georges LeMaitre.
    • In 1920s, a theory that the universe was created by a huge explosion, and all matter in the universe is still flying away from that explosion at enormous speeds. This theory named as the Big Bang Theory around 1930.

    Steady State Theory

    • It states that the counting of the galaxies in our Universe is constant and new galaxies which are forming continuously are filling the empty spaces which are created by those heavenly bodies which have crossed the boundary lines of observable Universe.
    • It was developed in 1948 by Fred Hoyle, Thomas Gold and Hermann Bondi.

    Pulsating Theory

    It states that it is the possibility that after some passage of time the expansion in the universe may stop. Then their may be the possibility of contraction. When this contraction will approaches to a particular size. Again the explosion will take place. As a result of this explosion the expansion of universe will start again. Hence it results in a pulsating universe in which there is alternate expansion and contraction of universe.


    • Galaxies are formed by group of starts, gases, and dust particles all are together by strong gravitational forces.
    • Galaxies are classified into three main types: spiral galaxies, elliptical galaxies, and irregular galaxies.
    • Milky Way (Akash Ganga) is the galaxy that contains our Solar System.
    • The Milky Way is a barred spiral galaxy.
    • The Andromeda Galaxy (also known as NGC 224 and M31) is the nearest spiral galaxy to our Milky Way galaxy.
    • MACS0647-JD is the farthest known Galaxy in the Universe.


    • Stars are glowing heavenly bodies. It emits light due to their high temperatures. It can be seen on a clear night.
    • The nearest star to us the sun. It is the brightest star.
    • The second brightest star is Alpha Centauri. The approximate distance of the star Alpha Centauri from earth is near about 4.3 light years.
    • Oldest start : HE 1523-0901 about 13.2 billion years old
    • Biggest star : VY Canis Majoris, 1,540 times the size of the Sun.
    • Smallest star : Gliese 623b. One tenth the mass of the sun.

    Black Hole

    • Black holes are the cold remnants of former stars, so dense that no matter—not even light—is able to escape their powerful gravitational pull.
    • While most stars end up as white dwarfs or neutron stars, black holes are the last evolutionary stage in the lifetimes of enormous stars that had been at least 10 or 15 times as massive as our own sun.
    • When giant stars reach the final stages of their lives they often detonate in cataclysms known as supernovae. Such an explosion scatters most of a star into the void of space but leaves behind a large “cold” remnant on which fusion no longer takes place.




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