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5.3 The Perfect Placement Of The Earth In The Solar System

Planets In The Solar System

1) The nine planets in the Solar System are at different distances from
    the Sun.

2) The Sun gives out heat and light which reach the planets.

3) The inner planets
    (a) Mercury, Venus, Earth and Mars are four planets that are nearest to
         the Sun.
    (b) These planets are made of rocks.
    (c) Each inner planet has an atmosphere.

4) The outer planets
    (a) Jupiter, Saturn, Uranus, Neptune and Pluto are called the outer planets
         or gas glants.
    (b) They are mainly made of gases.

                   Very hot                                                                                                   Very Cold
                                                                    Distance increases
                                                               Temperature decreases


Mercury




 ~ Nearest to the Sun.
 ~ Its temperature is too high to support
    life.








Venus





~ Second planet from the Sun and the nearest
   planet to Earth.
~ The hottest planet in the Solar System as a
    large amount of heat is trapped in its atmosphere.






Earth

~ Third planet from the Sun.
~ The only planet where there is life.
~ Has air, water and a suitable temperature.








Mars

~ A cold planet where almost all its water is
   frozen. No life exists here.
~ Its surface is covered with a thin atmosphere
   of carbon dioxide.
~ Also called the red planet because its surface
   is covered with red dust.





Jupiter

~ The largest planet.
~ All other planets can fit inside it.
~ Made up of gas.
~ Too cold to support life.







Saturn

~ The second largest planet.
~ The most beautiful planet as it is
   surrounded by three wide rings.
 ~ Made up of gas.
~ Colder than Jupiter and too cold to
   support life.





 Uranus

~ A greenish blue planet because of the
   presence of methane in its atmosphere.
~ Surrounded by narrow rings.
~ Lies on its side as it orbits the Sun.
~ Much colder than Saturn.







Neptune





~ Surrounded by a faint ring system.
~ Covered with a blue ocean of liquid
   methane.
~ As cold as Uranus.








Pluto

~ The smallest planet and furthest from
   the Sun.
~ The coldest of all the planets.








5) The placement of Earth in the Solar System makes it a perfect planet
     to support life. As the third planet from the Sun, it receives enough
     light and heat from the Sun.

 ~ Moderate surface temperature
~ 70% of the Earth's surface is covered
   with water.
~ A layer of atmosphere surrounds the
   Earth






6) The temperature of the Earth is suitable to support life because it is not too
    hot or too cold.

7) The Earth's surface contains enough water for the survival of living things.

8) The atmosphere of Earth consists of gases in the correct composition to
    support life.
    (a) Oxygen is needed for breathing.
    (b) Carbon dioxide is needed for plants to make food.
    (c) It protects the Earth from harmful rays of the Sun.

9) (a) The other planets either receive too much or too little heat.

    (b) The atmosphere of the other inner planets is too thin and poisonous to
          living things. For example, 95% of the atmosphere on Mars consists of
          carbon dioxide. The atmosphere of the outer planets is also not suitable
          to support life.

    (c) These planets connot support life because they

• are either too hot or too cold
• do not have enough air and water

10) If the Earth were much further from the Sun:         

• The temperature on Earth would drop drastically. It would be very much cloder.
•  Huge sheets of ice would cover most parts of the Earth.
• All living things would die.

11) If the Earth were nearer to the Sun:

• The temperature on Earth would rise and the condition would become hotter.
• Water on Earth would evaporate. Deserts would be formed.
• All plants and animals would die because there would be no water.

5.2 The Relative Size and Distance Between The Earth, The Moon anf The Sun

1) The Sun is very huge when compare to the Earth and the Moon.

2) The ratio of their diameters is as follows:

the Sun

the Earth













the Moon























       Ratio of diameter:  400 : 4: 1

• The Sun is 400 times bigger than the Moon.
• The Sun is 100 times bigger than the Earth.
• The Earth is 4 times bigger than the Moon.

3) The ratio of the diameters is only a rough estimate.

4) The actual diameters of the Sun, the Earth and the Moon are as follows:

	The Sun	The Earth	The Moon
Diameter (km)	1391016	12756	3480

• The Earth is not round. The diameter from the north pole to the south pole is 12714 km.
• The diameter at the equator is 12756 km.
• The ratio of  the diameter of the Sun to the diameter of the Earth is actually about 110 : 1.

The Relative Distance From The Earth To The Sun And From
The Earth To The Moon

1) The following are the distances between the Sun, the Earth and the Moon.

Distance	Between the Sun and the Earth	Between the Earth and the Moon
Distance (km)	150 000 000	382 500

2) The relative distance of the Earth to the Sun and of the Earth to the Moon is as follows:

                                   Earth to Sun               :              Earth to Moon

Approximate
ratio of distance:            400                          :                       1

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.

Asteroids

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.

                                                                    Asteroids


Meteors

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
     meteor.




Meteor







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


Comets

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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