In this chapter you will learn:

  1. The Solar system

  2. What are asteroids and comets?

  3. What is called Red-shift?

  4. What is Big Bang theory?

The Solar system

Our solar system is a small part of the Milky Way galaxy.

There are eight planets in our solar system.

The planets of the solar system are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

All planets move in elliptical orbits around the sun due to its force of gravitational attraction.

Pluto is a dwarf planet. These planets are like objects that orbit stars.

The Sun

The Sun is the biggest and most massive object in our solar system. The Sun was formed from a cloud of dust and gas pulled together by gravitational attraction.

It has a surface temperature of approximately 6000°C. The sun contains 99% of the Solar Systems mass. The Sun is the nearest star to Earth.


Moons are natural satellites that orbit a planet. Many planets have moons. Saturn has more than 50 moons. The Earth has just one moon.


Asteroids are oval shaped lumps of rock or metal that orbit the Sun in the asteroid belt between Mars and Jupiter.


The Solar System also contains some other small objects, such as comets and asteroids. Comets are made up of rocky material, dust, ice and frozen gases. Comets orbit the sun in elliptical paths.


All Star form from a clouds of dust and gas in space, known as a nebula.

A supernova is a massive explosion of a red supergiant. Supernova results from the rapid collapse and violent explosion of a massive star.

Medium mass stars like the sun form red giant. When all the hydrogen has been used up in the fusion process, larger nuclei begin to form and the star may expand to become a red giant. Stars spend approximately a few thousand to 1 billion years as a red giant.

The exploding supernova throws the outer layer of dust and gas in space, leaving a dense core called a neutron star.


The Milky Way is a barred spiral galaxy that contains over 200 billion stars.

The size of orbit depends on object's speed. The stronger the gravitational force, the faster the object needs to travel to remain in orbit.


The dark lines in the spectra from distant galaxies show that the radiation has undergone an increase in wavelength. They are moved or shifted towards the red end of the spectrum. This is called red-shift.

More distant galaxies have greater red-shift than nearer ones.

More distant galaxies are moving faster than nearer ones.

Big Bang theory

The Big Bang theory suggests that about 13.8 billion years ago the whole Universe used to be a very small, extremely hot and dense region. From this point, the whole universe expanded rapidly outwards as it is now.