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on April 27, 2012

                 What is the universe ?

We will try to understand the meaning of universe by taking an imaginary journey through space. your spaceship is now blasting off into space.

You are now 1.6 million (1.6 x 10 6) kilometers into space . The earth looks big and bright  in the darkness of space. The moon looks small.

         How was the universe formed ?

In the beginning , there was just a point of infinite density and energy. Some 15 billion years ago, a fiery explosion now called the “big bang “  occurred . Immediately after the explosion , the universe  expanded rapidly from the size of a pin to about 2,000 times the size  of the sun.When the universe  was less then a second old , it was dense as iron and it was also opaque . After 500,000 years , the universe gradually cooled to ~ 3,000oK. The elementary particles  fused to formed hydrogen and helium gas – the life in blood of the universe .  Hydrogen and helium formed gas pockets at random .In these pockets proto-galaxies  began to form . Between one and two billion years after the big bang , the proto-galaxies gave birth to galaxies, stars and another member of the universe.

         Is the universe expanding ?

The ever expanding universe

Till the early part of the twentieth century, astronomers believed that the universe was infinitely large , but did not change size or shape.

However , towards the end of the 1920’s, Edwin p. Hubble showed that , the galaxies were moving away from each other and moving in all directions. That is, the universe is expanding all the time in all directions.

     Edwin Powell Hubble (1889 – 1953)

Hubble is considered to be the founder of extragalactic astronomy – the branch of astronomy that studies the existence of other galaxies . He was  the first to observe the evidence of the expansion of the universe . He discovered that all nebulae in the sky are not part of the Milky Way galaxy . until his observation in 1924 , astronomers believed that all the nebulae were part of our galaxy.

Hubble is made his second major discovery – In 1927 – that all galaxies he observed were  moving away from our galaxy . In 1927 – the universe was expanding. H u b b l e  received many honors for his outstanding contributions to astronomy . The most advanced telescope to study intergalactic world is named after him.

After the Big Bang, Big crunch ?

Will the universe expand forever ?Or will it collapse at some point of time signify the end?

The density of the hydrogen atoms/m3 and the fate of the universe

Some, modern astronomers believe that : if the density of the universe is less than 3 hydrogen atoms/m3, its gravity is not enough to hold the matter together; i.e the universe will expand forever . If its density is more than this , the gravity will cause the collapse of the universe and the big crunch will occur.

           The sun – our nearest star

The distance between the sun and the earth is ~ 150,000,000 km. So , the light rays from the sun have to travel 150,000,00 km to reach earth. Astronomers have found that a ray of light from the sun covers this distance in 8.3 minutes.


Ancient sky- watchers or astronomers noticed that “stars”  that did not twinkle “wandered” through the sky . They called these “stars”, wanderers or planet (Greek word).

They named them after their gods – Venus,jupiter,Mars. According to them ,  the sun and the moon were also planets ! Now we know better. planets “shine” steadily . They do not have light of their own .They merely reflect sun’s light. They do not “twinkle”, because their flat discs reflect a lot of light. We can view the surface of a planet through a telescope .


Galaxies are system or families containing millions of stars . In addition to stars , galaxies also contain cosmic dust and gases .Sir William Hershel, the famous 18 th century  astronomer , called them “island in the sky”. There are millions of galaxies in the universe . Galaxies are millions of light – years apart from each other . There is vast empty space between them.

                  Milky Way galaxy


The Milky Way galaxy contains around 200 billion stars. The stars are too far away from us to be seen  individually or by the naked eye . The light from these stars forms a glowing haze in the sky as their light blends with the inter-stellar dust and gas.

This glow obviously has been seen by people from the early times.  The ancient Egyptians called it Road of Souls and the bushmen of the Kalahari desert called it the Blackbone of Night. In India, it is called Akash Ganga. Astronomers call it the Milky Way galaxy , our home in the vast universe.


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