Formation of galaxies & solar system:

(1) The origin of universe occurred by Big-Bang theory, 20 million years ago.

(2) Our universe is formed by thermonuclear explosion of cosmic material.

(3) Our universe has about 100,000 million galaxies, one galaxy has about 10,000 million stars. Sun is also a star. Our galaxy is Akash Ganga or Milky way.

(4) 9 Planets namely – Mercury, Venus, Mars, Earth, Jupitor, Saturn, Uranus, Neptune, Pluto, along with comets, materoids , asteroids, & sun in the centre ,  all constitute the solar system.

(5) Cosmic material from which galaxies were formed is called Nebulae.

(6)The universe is very old – almost 20 billion years old. Huge clusters of galaxies comprise the
universe.

(7)The universe expanded and hence, the temperature came down. Hydrogen and Helium formed sometime later.
The gases condensed under gravitation and formed the galaxies of the present day universe.

(8)Earth was supposed to have been formed about 4.5 billion years back. There was no atmosphere on early earth. Water vapour, methane, carbon-dioxide and ammonia released from molten mass covered the surface.

(9)The UV rays from the sun broke up water into Hydrogen and Oxygen and the lighter H2 escaped. Oxygen combined with ammonia and methane to form water, carbon-dioxide and others. The ozone layer was formed. As it cooled, the water vapor fell as rain, to fill all the depressions and form oceans. Life appeared 500 million years after the formation of earth, i.e., almost four billion years back.