UNIVERSE // Big Bang // Galaxy// Milky way

 About the Universe 

On a fine bright night when you look uo at sky , it seems to be studded with stars . Little do you realise that each of the STARs is far bigger than the earth on which we live . Some of the larger ones have been estimated to be many millions of times the size of earth . These stars are not scattered regularly in space ; they appears in clusters , better describes as Galaxies or nebulas . Each galaxy may contain as many as 100 millions stars . 

It is believed that earth own  (the milky way)  alone contain as many as 100000 millions stars.

Definition of Universe : It is defined as the totality of everything that exists , including all physical matter and energy , the planets, stars , galaxies , and the contents of intergalactic space .

The study of universe is known as Cosmology.

The diameter of the universe is 10^8 light years.

Origin of  the Universe

The most popular argument regrading the origin of the universe is the Big Bang Theory . It is also called expanding universe hypothesis. Edwin Hubble , in 1920 , provided evidence that the universe is expanding . As time passes, galaxies move further and further apart. 

  

Theories regrading  the origin the the universe

 

Big-Bang Theory by E.Georges Lamaitre

Steady state Theory by Thomas Gold and Herman      Bondy

Pulsating Universe Theory by Dr. Allen Sundes

InflationaryTheory by Alan H Guth.

BIG BANG THEORY

The BiG Bang theory considers the following stages in the development of the universe.

 1. In the beginning , all matter forming the universe existed in one place in the form of a "tiny ball" (Singular atom ) with an unimaginably and infinite density. 

 2. At the big bang the " tiny ball" exploded violently . This led to a huge expansion . It is now generally accpeted that the event of big bang took place 13.7 billion year before the present.

 The expansion continues even  to the present day . As it grew , some energy was converted into matter. With in first three minutes from the big bang event , the first atom began to form.

 3. Within 300000 years from the big bang  , temperature dropped to 4500k and gave rise to atomic matter. The universe became transparent. 

  The expansion of the universe means increase in the space between the galaxies. An alternative to this was Hoyle s concept  of steady state .It considered the universe , universe , scientific community at present favours argument of expanding universe.

Galaxy 

A galaxy is a vast system of billions of stars , which also contains a large numbers of gas clouds (mainly of hydrogen gas ) and dust , isolated in the space  from similar system.

 There are about 100 billion galaxies in the universe , and each galaxy has , on an average , 100 billion stars  .

So the total number of stars in the universe is 10^22 stars.

The MILKY WAY Galaxy is the home of the earth and our solar system. It is spiral in shape.

Milky way Galaxy was formed 5 billion years after the  big bang. The first person to see this galaxy was Galileo Galilei.

Latest known galaxy is known as Dawrf Galaxy .

Where is earth in milky way:

Earth is located in one of the spiral arms of the Milky Way (called the Orion Arm) which lies about two-thirds of the way out from the center of the Galaxy. Here we are part of the Solar System - a group of eight planets, as well as numerous comets and asteroids and dwarf planets which orbit the Sun.