Friday, 7 December 2012

5.1 The Solar System

The Constituents Of The Solar System
1) The Solar System consists of:
  • the Sun
  • planets
  • natural satellites
  • asteroids
  • meteors
  • comets
2) (a) The Sun is the centre of the Solar System.
    (b) It is a star because it gives out light and heat. It is the only star in
         the Solar System.

    (c) The Sun is the biggest body in the Solar System. It consists af a ball
          of hot gases.

Planets Of The Solar System

1) Planets are bodies in the Solar System that move round the Sun.
    (a) A planet does not give out its own light and heat.

    (b) We can see other planets from Earth because they reflect light
          from the Sun.

2) There are nine planets in the Solar System:
  • Mercury
  • Venus
  • Earth
  • Mars
  • Jupiter
  • Saturn
  • Uranus
  • Neptune
  • Pluto (Since 24 August 2006, Pluto is classified as a dwarf planet.)
3) Each planet moves in a large oval path called an orbit. It also rotates on its
    own axis.

                                                  The orbit of the Earth round the Sun
  • The planets that are nearer to the Sun take a shorter time to move around the Sun because they have smaller orbits.
  • The planets that are further from the Sun take a longer time to move around the Sun because they have bigger orbits.
  • For example, Mercury takes about 88 days to move around the Sun while Neptune takes about 165 years.
4) When a planet is further away from the Sun, its orbit is bigger. For example,
     the distance between Jupiter and the Sun is longer than the distance between
     the Earth and The Sun.

5) The time taken by the planets to make one complete movement round the Sun
    depends on their distance from the Sun.

 Positions of planets from the Sun

Natural Satellites

1) Some planets have large bodies that orbit around them. These bodies are
    called natural satellites.

2) The Moon is the only natural satellites of thw Earth. It is smaller than the
    Earth. It orbits round the Earth and the Sun.

3) Mercury and Venus do not have their own natural satellites. Some planets
    have more than one natural satellites.

4) Natural satellites do not give off light or heat. They reflect light from the
    Sun and can be seen from Earth.


1) Asteroids are bodies made up of metals and rocks.

2) Most asteroids are found in the asteroid belt between the orbits of Mars
    and Jupiter.

3) More than 10000 asteroids and more are discovered every month. Ceres
    is the first asteroid to be discovered. It is the largest asteroid.

4) Some asteroids come near the orbit of the Earth. Someday, one of these
    asteroids could hit the Earth.

5) An asteroid hit Earth 65 million years ago in Mexico.



1) A meteoroid is a piece of rock or metal that floats in space.
    (a) Meteoroids come in many shapes and sizes but most of them are small.
    (b) There are millions of meteoroid in space.

2) When a meteoroid enters the atmosphere of the Earth, the friction between
     the meteoroid and the air causes it to glow and give off light. It is called a


3) A meteor looks like a streak of bright light that is seen across the night sky.
    It is also commonly called a shooting star.

4) (a) A meteor that has landed on the surface of the Earth is called a meteorite.
     (b) When a meteorite hits the Earth, a crater or a hole is formed in the ground.

                                                       A crater formed by a meteorite


1) A comet is a lump of ice which consists of frozen gases and dust.

2) Comets move around the Sun in long orbits. They take years to complete
    one orbit.

3) Most comets spend their time beyond the Solar System. When they enter
    the Solar System and come near the Sun, they can be seen from Earth.

4) When a comet comes near the Sun, the heat of the Sun causes the ice at its
    centre to melt. This causes the comet to glow and a long tail of gas and dust
    is visible.

5) The most famous comet is Halley's Comet.

                                                                 A Halley's Comet

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