Big bang theory, Light year, Galaxy and Nebulae (Class - 9)

BIG BANG THEORY

* 15billion years ago, there was a cosmic mass. (smaller than the dot)
* It was made up of hot and dense matter.
* A great explosion shattered the cosmic mass into countless tiny pieces.
* This explosion is known as “Big Bang”.
* The Big Bang resulted in the formation of nebulae.
* In the course of millions of years, the temperature and density of nebulae

increased till thenebulae increased till the nebulae collapsed by itself.
* As a result, new stars were born.
* The hydrogen within these stars got converted into helium, sun, star, was born
in this way.

MILKY WAY OR AKASH GANGA

• On a cloudless night, one can see a cluster of stars forming a narrow band in the sky. This is called MILKY WAY OR AKASH GANGA.It is a galaxy containing as many as 1,00,000 million stars. Sun is a medium sized star in the Milky Way galaxy. There are millions of galaxies in the Universe.

LIGHT YEAR

• Universe is vast in size.
• Distances between heavenly bodies cannot be expressed in units like kms or miles
• If you drive on a highway at 60 k.m.s per hour in one hour you may get to Hiriyuru.
  Steady speed!
  If you keep on driving after 4 hours you would reach Bangalore.Steady speed - no stops
• If we could keep on and on - - ---------
• If you could drive to the Moon at 70 miles per hour, 230,000 miles or about 400,000 km, it would take you 3400 hours, or 140 days.
• A light year is the unit adopted for measuring distances in the Universe. A ray of light travels at a speed of 30,000 km per second.
• Light and heat comes from the Sun.
• It is a long way away ! 146 million km
  If you could drive to the Sun at 70 miles per hour, it would take over 50 000 days.
  = 150 years
  – longer than we live !
• Light travels very, very fast!
• It takes 8 minutes for light to reach us from the Sun!
• Light travels 300 000 kilometres through space every second!
• A light year is the distance, which a ray of light would cover in a year’s time.
• After the Sun, the ALPHA CENTAURI is the nearest star to the earth..
  Also called PROXIMA CENTAURI & 4.3 light years away.

GALAXY

• Galaxy is a collection of billions of stars, found clustered together due to their own gravity. The arrangement of the stars gives rise to different shapes , consisting of varying numbers of stars.

Nebulae

• They are cloud like formations containing dust and hot gases. They appear as misty patches of light spanning the sky.
• They appear as dark patches or bright luminous clouds, depending on the colour of the sky which forms their background