◄Unit 2: Elements of a mapUnit 4: The structure of the earth►

Unit 3: The Earth in relation to the universe

  • Unit 3: The Earth in relation to the universe

    h

    By the end of this unit, you must be able to analyse the impact of the earth’s position and movements in the solar system.

    Unit objectives

    By the end of this unit, you must be able to:
    (a) identify different components of the universe
    (b) describe the earth and the solar system
    (c) state the earth’s movements and their consequences
    (d) show the relationship between longitude and time
    (e) define latitude and longitude.

    Components of the universe

    h

    Do this in groups of four under the guidance of your teacher.
    1. Go outside your classroom for five minutes.
    2. Observe the sky.
    3. Write down what you have observed.

    4. Let each group member say what is seen in the sky at night.
    5. Write down your points.
    6. Compile your points and share them with other members in a class presentation.

    y

    Do this individually and share the findings with other members of your class.

    Study the pictures shown below.

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                    Fig 3.1
    k

                     Fig 3.2

    1. Compare the two pictures showing the sky at different times.

    2. Write down the differences that you can observe.
    3. Explain why you think there is a difference in the sky at night and at day time.
    4. Share your findings with the rest of the class.

    Definition of the universe

    The term universe refers all of space including everything that exists in it. This includes the stars, the galaxies, the planets, matter and energy . It also has empty space with particles and interstellar gas. The universe is also known as the cosmos. During day time, it is common to see the sun. This is one of the heavenly bodies that exist in space. However this depends on one’s geographical location. The universe has no specific shape. It is endless space. Scientists have not fully explored the universe due to its vast and seemingly unending nature. They are still making discoveries in order to understand the universe better.

    j

    Do this in groups of five.
    1. Use the Internet, geography textbooks and photographs to find out the elements that constitute the universe.
    2. Write down notes on your findings.
    3. Choose a group leader who will share the findings of your group with other class members in a class presentation.

    Components of the universe

    a

    Do this in groups of three.
    1. Using the Internet and geography textbooks, find out other heavenly bodies found in the universe.
    2. Write them down in your notebooks.
    3.The universe is made up of planetary bodies that move or revolve around the sun. They
    include the following. Present your findings in class.

    • Stars
    • The sun
    • Clusters
    • Galaxies
    • Planets
    • Earth
    • Moons
    • Asteroids
    • Meteors
    • Comets

    (a) Stars
    Stars are luminous heavenly bodies that give out light. In most cases, stars have very
    high temperatures. There are many stars in the universe. Each star is associated with planets and moons.

    e

         Fig 3.3 Stars in the sky at night

    (b) The sun
    The sun is one of the stars that are found in the universe. It is the only star that gives out its own light. Other stars in our universe reflect light from it. It is located in the middle of the solar system. The sun is near the earth’s atmosphere. All the known planets and other heavenly bodies revolve
    around it. The planets and heavenly bodies revolve around the sun following specific paths
    known as orbits. This revolution occurs because the sun pulls them towards it. They also use their own gravitational force to pull towards their centres and end up being in a circular motion.

    y

    Fig 3.4 The earth orbits the sun

    (c) Clusters
    Star clusters are a group of stars that share a common origin. They are held together by
    the force of gravity.

    f

           Fig 3.5 A cluster of stars.

    (d) Galaxy
    A galaxy is a large collection of gas, dust and billions of stars held together by gravity. One galaxy can have hundreds of billions of stars and be as large as 200,000 light years across. These stars are still held together by the force of gravity. For example, our planet, Earth is found in the Milky Way galaxy. It derived its name from its milky, appearance of a dim glowing band arching across the night sky. There are also other galaxies in the universe.

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         Fig 3.6 The Milky Way galaxy.

    (e) Planets
    These are heavenly bodies that revolve around a star following specific orbits.

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               Fig 3.7 Planets in the solar system

    The solar system consists of eight planets and the sun. The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The Earth is the only planet that has been known to support life. 

    y

    Work in pairs.
    1. Go outside the classroom. Describe what you can see on planet earth that makes it able to support life.
    2. Write down your findings in your notebooks.

    3. Present your work in a class discussion.

    (f) Moons
    The moon is another heavenly body that is found in the universe. It is a natural satellite of the earth. There is only one moon that attends to our planet Earth. Other planets also have satellites that attend to them. It is estimated that there are about 179 satellites that attend to all the planets and planetoids. These satellites form part of the universe.

    h

      Fig 3.8 The moon as observed from the earth

    (g) Asteroids
    Asteroids are small, airless rocky bodies revolving around the sun between Mars and Jupiter. They are too small to be called planets. This is because they never fully developed into planets. They are sometimes referred to as planetoids or dwarf planets. They range in size from tiny particles to large bodies hundreds of kilometres in diameter. It is not easy to see the smallest asteroids. Since they have little gravity, they are irregular in shape. Asteroids are minor members of the solar system. They form part of the universe.

    w

          Fig 3.9 Asteroids in space

    heart Meteors
    Meteors are fragments of rock and metal that fall to Earth from space. They are known to fall as they break away from other bodies such as asteroids. They are of different sizes. Some are as small as a fraction of a millimetre. Others are as big as a football pitch or bigger. The Earth’s gravitational force causes the meteorites to accelerate to over 11.2 kilometres per second. As they enter Earth’s thick atmosphere, they rapidly slow down due to the friction. They then glow, flashing across the sky like fireworks, before finally crashing to the ground.

    Meteors are popularly known as shooting stars. When they enter the Earth’s atmosphere, they appear as short-lived long thin lines of light. This light suddenly disappears into vapour or ash.
    This happens before the meteors reach the Earth’s surface. The bright light is formed out of friction between the meteor and the atmospheric air. Meteors are minor members of the solar system. They form part of the universe.

    c

        Fig 3.10 Meteors in outer space

    Meteors that fail to vapourise or burn up reach the Earth’s surface as rocks. They are referred to as meteorites. Some hit the Earth’s surface with a great impact forming craters. When meteorites reach the Earth’s surface, they cause great damage. However, in most
    case the meteors fail to enter the Earth’s atmosphere. This is because of the following
    reasons.

    • Most of them burn up before they reach on the Earth’s surface. This is due to the high speeds and powerful friction.
    • The moon safeguards the Earth from meteoroids. Therefore, most of them land onto the moon’s surface. This is why there are many craters on the moon’s surface.

    a

    Do this in groups of three.
    1. Using space photographs, the Internet and textbooks, find out what would happen to our environment if meteors hit the Earth’s surface.
    2. Come up with appropriate measures that humans could take to ensure that we protect our  environment should that happen.

    (i) Comets

    Comets are small heavenly bodies that revolve round the sun along very elongated orbits. They are made up of frozen gases, ice and lumps of rocks. Comets cross the orbits of other planets as they move towards the sun.

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             Fig 3.11 Comets in space.

    When they get closer to the sun, the heat vapourises the frozen gases. This produces a glowing head called coma and a tail.The tail extends for millions of kilometres. This tail points away from the sun. As thencomets move away from the sun, the gases condense and the tail disappears.

    Task 1.

     (a) Define the term universe.
    (b) Outline the components of the universe.
    2. (a) Describe the phases of the moon.
    (b) Explain the meaning of a satellite.
    3. (a) What is an orbit?
    (b) Why should planetary bodies revolve around the sun?
    5. Describe the difference between the sun and other stars.
    6. (a) With specific examples, define the term planet.
    (b) Explain the characteristics of the moon that is attendant to planet Earth.
    7. Describe the following terms as used in geography.
    (a) Asteroids       (b) Planetoids
    (c) Meteors        (d) Meteorites
    (e) Comets         (f) Shooting stars

    Constellations and galaxies

    o

    Work in pairs. Your teacher will provide with two photographs.
    1. Using the Internet and geography textbooks, find out the meanings of the following:
    (a) constellations
    (b) galaxies.

    2. Look at the photographs that yourbteacher provided you with and state the differences between the two.
    3. Write down the differences in your notebook.
    4. Present your findings in class.

    Constellations

    A constellation is a group of stars that forms a pattern in the sky. This is as seen when viewed from the earth.
    There are 88 constellations in our solar system. The Southern Cross commonly referred to as a Crux is the brightest while Hydra is the biggest. The following pictures show different constellations and their appearances in the sky.

    d

          Fig 3.12 The big dipper

    e

             Fig 3.13 Orion.

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    ng

    kj

    c

    Do this in groups of four.
    1. Go outside the classroom.
    2. Using threads and short sticks, demonstrate the patterns of the following constellations:

    (a) The big dipper
    (b) The Southern Cross (Crux)
    (c) Orion
    (d) Pegasus.

    Galaxies

    s

    Do this in groups of three. Use the Internet, geography textbooks and journals to do the
    following.
    1. Define the term galaxy.
    2. Name and describe different galaxies.
    3. Find out whether the Milky Way galaxy is spiral, elliptical or irredula.
    4. Write down your findings in your notebook.
    5. Share your findings in a class discussion.

    As you learnt earlier, galaxies form part of the universe. A galaxy is a big collection of gas, dust and billions of stars held together by gravity. One galaxy can have hundreds of billions of stars. It can also be as large as 200,000 light years across.
    (a) The Milky Way galaxy – This galaxy has a bright central core with a high density of stars and a flattened disk surrounding it. Its name “milky” is derived from its appearance as a dim glowing band
    arching across the night sky. This galaxy contains our solar system.

    v

               Fig 3.20 The Milky Way galaxy.

    (b) The Andromeda galaxy – This galaxy gets its name from the area of the sky in which it appears, the constellation of Andromeda. It is the closest big galaxy to the Milky Way.

    f

           Fig 3.21 The Andromeda galaxy.

    (c) Black Eye galaxy – It has a spectacular dark band of absorbing dust in front of the galaxy’s bright nucleus, giving rise to its nicknames of the “Black Eye” or “Evil Eye” galaxy.

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           Fig 3.22 The Black Eye galaxy.

    (d) Bode’s galaxy – This is named for Johann Elert Bode who discovered this galaxy in 1774.

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             Fig 3.23 The Bode’s galaxy.

    (e) Cartwheel galaxy – Its visual appearance is similar to that of a spoked cartwheel.

    b

           Fig 3.24 The Cartwheel galaxy.

    (f) Cigar galaxy – This galaxy appears similar in shape to a cigar.

    f

    Fig 3.25 The Cigar galaxy

     (g) Comet galaxy – This galaxy is named after its unusual appearance, looking like a comet.

    p

             Fig 3.26 The Comet galaxy.

    heart Tadpole galaxy – The name comes from the resemblance of the galaxy to a tadpole. This shape resulted from tidal interaction that drew out a long tidal tail.     

    e

                 Fig 3.27 The Tadpole galaxy .

    (i) Whirlpool galaxy – From the whirlpool appearance this gravitationally disturbed galaxy
    exhibits.      

    c

              Fig 3.28 The Whirlpool galaxy

    Task 3.2

    1. What is a constellation?
    2. Give the names of the following.
    (a) The brightest constellation.
    (b) The biggest constellation in our solar system.
    3. Give the names of specific examples of constellations.
    4. Define a galaxy.
    5. Name any three examples of galaxies.

    The earth and the solar system

    d

    Do this in pairs.
    1. Go outside your classroom and observe the sky.
    2. Record what you see in your notebook.
    3. Explain the importance of the sun to human beings and to the environment.
    4 Share your findings in a class discussion.

    When you go outside, you can see a bright heavenly body that gives us light. The heavenly body is known as the sun. We have already learnt that we have stars in the universe. The most important star is the sun. Plants, animals and human beings all depend on the energy provided by the sun. The sun is a star that is at the centre of the solar system. It is the only star that gives out its own light.

    k

    Do this in groups of three.
    1. Discuss the importance of the sunshine.
    2. Explain what would happen to our environment if:
    (a) the sun did not produce light
    (b) the sun gave too much heat.

    The solar system

    r

    Work in pairs.
    1. What is the meaning of the solar system?
    2. Name the components of solar system.
    3. Name the heavenly body that holds planets in the solar system.

    The word solar is derived from a Latin word sol that means the sun.

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                          Fig 3.29 The composition of the solar system.

    The solar system is a composition of the sun, the eight planets and other heavenly bodies. In the solar system, the planets and the heavenly bodies revolve around the sun. The eight planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. They occur in that order from the sun. Jupiter is the largest planet while Mercury is the smallest. Other heavenly bodies are
    smaller than the planets. They include; satellites, meteors, asteroids, satellites, comets and meteorites, gas and dust. The solar system exists in the universe. It is one of the components of the universe.

    The sun
    The sun is a star. A star has a bright sphere of hot gas. There are millions of stars in the space. The sun was formed about 4 to 6 billion years ago. It forms the central part of the solar system. All the bodies of the solar system revolve around the sun. The gravitational field of the sun holds elements of the solar system in orbit. The sun rotates in an anticlockwise direction on its axis. It takes about 25 days to complete a rotation at the equator. It also takes about 34 to 35 days to rotate at the poles. The sun is mainly made up of hydrogen and helium which are burning gases.
    The planets.

    The planets

    h

    Work in groups.
    1. Go outside your classroom to the playground.
    2. Draw eight different circles on the ground using chalk. The circles should be inside each other with spaces of about 2 metres apart.

    3. Choose some students to run as they go round the circles in an anticlockwise direction. They should begin at a slow speed and increase the speed gradually.
    4. Observe what happens. Explain why the above learners did not collide as they ran around.
    5. What is the geographical name given to the paths that the learners followed?
    6. What do you think would happen if the learners did not have specific paths to follow?

    A planet is a heavenly body which:
    (a) is made up of rocky solids
    (b) is oval in shape
    (c) is suspended in space
    (d) rotates on its own axis
    (e) revolves around the sun.
    The planets are grouped into two:

    (a) The inner planets: These are also referred to as the terrestrial planets. They are made up of silicate rock mantles. Their cores are composed of iron. They are the planets that are nearer the sun.They are:
    . Mercury           .Venus

    . Earth               . Mars

    (b) The outer planets: They are also called Jovian planets. They are:

                Jupiter        Uranus
                Saturn        Neptune

    Jupiter and Saturn are composed of gas while Uranus and Neptune are composed
    of ice. The planets revolve around the sun in an anticlockwise direction along paths known as orbits. The orbits are oval or elliptical in shape. Different planets take different lengths of time to make complete revolutions round the sun. This is because of their various distances from the sun. The period taken by a planet to make a complete revolution round the sun is known as a year. The earth takes 365 ¼ days to make a complete revolution round the sun. This period is one year on the Earth. Mercury takes 88 days to make a complete revolution round the sun. This is because it is near the sun. This is the shortest time taken by a planet to go round the sun. While revolving around the sun, the planets also rotate on their own axes. The planets and heavenly bodies are held in place by the gravity of the sun.

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    (a) Name the planets in the solar system.
    (b) Which planet supports life?
    (c) Suggest ways that humans can make planet Earth fit for human habitation.

    Table 3.1 The known planets of the solar system.

    Planet
    		 Key features
    Mercury
    		 • It is the smallest planet.
    • It is the nearest planet to the sun.
    • It completes its revolution in 88 days.
    • It is moonless.
    • It is about 70 million kilometres from the sun when it is at its farthest.
    When it is closest to the sun , it is at 47 million kilometres away.
    Venus
    		 • It is slightly smaller than planet earth.
    • It is one of the brightest planets in the universe.
    • It is almost similar to the earth.
    • It is moonless.
    • It is 108.9 million kilometres from the sun.
    • It takes 225 days or 0.165 Earth years to complete its revolution
    around the sun.
    Earth
    		 • It is the third planet from the sun.
    • It is the only planet known to support life .
    • It is 146 million kilometres from the sun.
    • It has one moon.
    • It takes 365 days to complete a revolution around the sun.
    Mars
    		 • It is slightly cooler than other planets.
    • It is 228 million kilometres from the sun.
    • It has 2 moons.
    • It takes 686.971 Earth days to complete a revolution around the sun.
    Jupiter
    		 • It is the largest planet.
    • It has 63 moons.
    • It takes 12 Earth years to complete one revolution round the sun.
    • It is 779 million kilometres from the sun.
    Saturn
    		 • It has a ring around it making it unique.
    • It has 62 moons.
    • It is 1.4 billion kilometres from the sun.
    • It takes 29.4 Earth years to complete a revolution around the sun.
    Uranus
    		 • It is the 7th planet in the universe .
    • It is the 8th 2.5 billion kilometres from the sun.
    • It has 27 moons.
    • It takes 84.3 years to complete a revolution around the sun.
    Neptune
    		 • It is the 8th planet from the sun.
    • It is 4.5 billion kilometres from the sun.
    • It has 13 moons.
    • It takes 164.79 Earth years to complete a revolution around the sun.

    (c) Satellites

    w
    Your teacher will provide you with photographs of satellites.
    (a) Classify the satellites as natural or artificial.
    (b) Write down the differences between the two in your notebook.
    (c) Share your findings with your classmates in a class presentation.
    • A satellite is an object that moves around a larger object. The moon is a satellite because it moves around Earth. Some planets are moonless meaning they have no satellites while others have many moons. In total, the solar system has 179 satellites. There are two types of satellites in our universe.
    • (a) natural satellites
    • (b) artificial satellites.

    • Natural satellites

    • These are heavenly bodies that float around planets passing through specific paths called orbits. They occur naturally in the outer space. A good example is the moon. It is a natural satellite.

    • d
    •         Fig 3.30 The moon is a natural satellite.

    • Artificial satellites

    • These are smaller objects in the outer space made by humans. They move around planets or moons. They are mostly used for scientific research, communication, weather monitoring and military purposes.

    • u
    •         Fig 3.31 An artificial satellite in space.

    • k
    • Use the Internet and geography textbooks:
    • 1. Find the relationship between the solar system and the universe.
    • 2. State the importance of the solar system in the universe. Write down your findings in your notebook.
    • 3. Share your findings with the rest of the class.

    • Task 3.3

    • 1. Explain what a planet is.
    • 2. Distinguish between the inner planets and outer planets.
    • 3. List examples of terrestrial planets and explain why they are called so.
    • 4. With the aid of a diagram, list the planets of the solar system in order of occurrence.

    • The moon
      The moon is a natural satellite of the earth.Moonlight is the illumination of the sun’s light. The moon does not produce any light of its own.

    • The moon’s diameter is approximately 3,476 kilometres. It is egg-shaped with the smaller end pointing towards the earth. It rotates on its axis. It also revolves round the earth in 27 days, 7 hours and 43 minutes. It takes 29 days, 12 hours and 44 minutes to get to a new moon. The moon therefore, completes its rotation and revolution at about the same time


  • Phases of the moon

    • r


    • Do this in pairs.
    • 1. From your own observation, how would you describe the changing appearance of the moon at different times ? Write these down in your notebook.
    • 2. Share with your classmates in a class discussion.

    • The moon has different phases. These phases refer to the different shapes of the illuminated part of the moon. These phases are as seen from Earth. The moon changes its phase in relation to the reflected sunlight depending on its position.

    • The following are the main phases of the moon.
    • 1. Primary phases.
    • • New moon
    • • First quarter
    • • Full moon
    • • Last quarter

    • 2. Intermediate phases.
    • • Waxing crescent
    • • Waxing gibbous
    • • Waning gibbous
    • • Waning crescent

    • New moon
      The new moon is completely dark on the first day. This happens when the side of the moon that receives sunlight faces away from the earth. The new moon appears when the moon is aligned with the sun and the Earth. During this period, the sun and the moon rise and set about the same time. The new moon is usually dark.


    • t
    •      Fig 3.32 The new moon.

    • Waxing crescent moon

    • Between the 1st and the 6th day after the new moon, the moon changes. The part that faces the earth begins showing a silver bright crescent shape. This happens to the moon as it moves around the earth.This shape continues to increase in size as days go by.

    • y
    •         Fig 3.33 Waxing crescent moon.

    • The first quarter moon

    • Seven days after the new moon, the moon completes a quarter of its journey around the earth. This is when we are able to see the half of it that receives sunlight. This happens when the moon is at a 90° angle to the earth and sun. This is the part that is illuminated. The other half is in theshadow. 
    •  z  
    •      Fig 3.34 The first quarter moon.
  • Waxing gibbous moon
  • This is the moon that appears between day 8 and 13. This phase appears when the part of the moon that receives sunlight grows bigger.

    • y
         Fig 3.35 The waxing gibbous moon.

    At this point, we view a bigger bright part of the moon as illustrated in Figure 3.35.
    Full moon
    Fourteen days after the new moon, the moon completes half of its revolution around the earth. During this phase, we see a complete circle of the moon exposed to sunlight

    v
              Fig 3.36 The full moon.

    Waning gibbous moon

    This phase appears between 15 to 21 days after the first phase of the new moon. From the earth, we see the lit disk of the moon decreasing or waning. This continues to decrease as days go by.

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         Fig 3.37 Waning gibbous moon.

    Last quarter

    This phase appears three weeks after the new moon. From the earth, we see half of the moon that is lit and half that is completely dark.

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    Waning crescent

    This phase occurs 23 to 28 days after the new moon. In this phase, the dark part of the moon is bigger than the lit side. From the earth, a bright crescent is seen. It keeps on decreasing until the whole disk of the moon is dark. This leads to day 0 when another new moon occurs.

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         Fig 3.39 Waning crescent moon.

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                      Fig 3.40 A summary of the phases of the moon.

    k
    Do this in pairs.
    1. Collect a used DVD disk and a torch.
    2. Hold the disk as you face your classmate.
    3. Ask your classmate to hold a brightly lit torch pointing towards the disk.
    4. Continue changing the position of the disk as you observe the light.
    5. Note down your observations.
    6. Discuss your observations with your classmate.
    7. Compare this to the different phases of the moon.

    Characteristics of the moon

    z

    Do research in pairs. Use the Internet and other geographical documents.
    1. Find out the unique characteristics of the moon as a component of the universe.
    2. Write down your findings in notebooks.
    3. Share your findings in a class presentation.

    The moon has the following characteristics.

    (a) It has a cold surface. Although it gives out light, the temperatures on its surface are so low. It does not produce its own light. It reflects light from the sun that is projected onto planet Earth.

    (b) It is a dry globe. It has neither rain nor water bodies. This means it has no moisture in its environment.
    (c) Its surface is dominated with craters.Craters are depressions or holes. They are caused by other heavenly objects that fall on it with great force.

    (d) Its landscape is made up of rocks and dust. When other heavenly objects fall onto the moon, they break the rocks on the surface. As they break,they are crushed into dust.

    (e) It has no or low gravitation force. On most parts of the moon, there is very little gravity. On other parts, there is no gravity at all. The gravitational force of the moon causes periodic rising and falling of sea and oceanwaters. This causes tides.

    (f) Its atmosphere is very limited.This means that there is little air surrounding it.

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    Fig 3.41 The surface of the moon is full of
    craters.

    Eclipse

    b
    Do this in groups of three.
    (a) Collect a torch and a football. The ball represents a heavenly body while the torch represents the sun.
    (b) One of you should hold the ball and the other one the lit torch.
    (c) Hold the lit torch and the ball aligned in a straight line.
    (d) Note down your findings.
    (e) One group member should stand in front of the source of the lit torch.
    (f) Observe what happens to the ball.
    (g) Write down your observation in your notebook.
    heart Answer the following questions in your group.
         (i) What happened to the ball when the torch was lit?
         (ii) What happened when an obstacle came in between the source of light and the ball?

    The answers to the questions in Activity 3.20 explain what happens between the sun, moon and the earth. This happens when the moon moves around the earth. The word eclipse comes from the Greek word ekleipsis which means abandonment.
    An eclipse is the blocking off of the light of a heavenly body. This light is blocked by another heavenly body that passes in front of it.
    An eclipse occurs when the sun or moon is hidden from an observer on earth. The sun is larger than the earth and the moon.
    This results in the formation of zones of shadows. The inner total shadow is called the umbra. The outer partial shadow is called the
    penumbra.

    Types of eclipse

    There are two types of eclipses.
    •  The eclipse of the moon (lunar eclipse).
    •      The eclipse of the sun (solar eclipse).
    Eclipse of the moon (lunar eclipse)

    This occurs when the earth comes between the moon and the sun. The earth blocks the sun’s light from reaching the surface of the moon. The earth casts its shadow on the moon, making it
    completely dark.
    During the eclipse, the moon may be visible but without its bright illumination. The moon remains in darkness for about two hours. This is because the earth is larger than the moon. It therefore takes a longer period to move the path of the sunlight. Lunar eclipses take place at night and only during
    the full moon.
    h 

    Eclipse of the sun (solar eclipse)

    This eclipse occurs when the moon comes between the earth and the sun. The moon casts its shadow on the Earth’s surface. It obscures or hides the Earth from the sunlight. Only a small section of the Earth experiences a total solar eclipse. It lasts for about seven and half minutes. The solar eclipse occurs at daytime.

    k
                 Fig 3.43 (a) A drawing showing the lunar eclipse.
    c
                      Fig 3.44 (b) An illustration of the solar eclipse.


    n

    b
    Do this in pairs. Use the encyclopedia, the Internet and geography textbooks.
    1. Carry out further research on the occurrence of the solar and lunar eclipses.
    2. Compile a report of your findings.
    3. Share your findings in a class presentation.

    The characteristics of the Earth

    The Earth is one of the eight planets in the solar system. It is the third planet after Mercury and Venus. It is believed that the earth was formed about 4,600 million years ago. It was formed when
    hot gaseous material broke away from the sun. When this happened, the denser materials consolidated first. They collected at the centre to form a core. The less dense materials collected around the core to form the mantle and the crust. The crust cooled at a faster rate than both the mantle and the core. It therefore hardened. The interior of the earth still maintains very high
    temperatures.
    The earth is surrounded by a thin layer of gases that is called the atmosphere. The atmosphere is held into place by gravity.About 71% of the total surface of the Earth is occupied by water. Only 29% is occupied by land.

    Elements of the earth

    b
    Do this in pairs.
    1. Use the Internet and geography textbooks to critically study the components of the earth.
    2. Compare them with those of other planets in the solar system.
    3. Find out the components that make the earth unique.
    The earth is made up of the following.
    • The core
    • The mantle
    • The crust
    • The atmosphere
    • The hydrosphere

    The core

    The core of the earth is made of dense material. This material collected during the formation of the earth. The core consists of an outer and an inner core.

    The mantle

    This part lies between the crust and the core. It consists of hot, dense, semi-solid rock. It is about 2,900 kilometres thick.

    The crust

    It is the outermost layer of the earth. It is made of a variety of igneous, sedimentary
    and metamorphic rocks.

    The atmosphere

    This is the thin layer of gases that surrounds the earth. It is held onto the earth by the force of gravity. It consists of a mixture of gases like nitrogen, oxygen, water vapour and carbon (IV) oxide.

    The hydrosphere

    This is composed of all the water on the earth’s surface. The oceans and seas cover 71% of the earth’s surface. This accounts for about 97% of the total waters on earth.
    v

    Uniqueness of the earth

    The earth is the only planet that is known to support life. This is because it has liquid water
    on its surface. The water is in amounts that are conducive to life evolving. The earth has plates that move over an underlying mantle.
    It also has an atmosphere. The atmosphere shelters it from the sun’s rays. These attributes make it unique among the other planets.

    m
    Do this in groups of three.
    1. Go outside the classroom.
    2. Identify evidences of the factors that support the Earth’s uniqueness.
    3. Suggest ways in which humans can conserve the environment to make the Earth remain habitable.
    4 Use the findings of your discussion to make a class presentation.

    The shape of the earth
    b
    Do this in groups of five.
    Your teacher will provide you with whole pumpkins. Follow the instructions given below. After the activity, write down the findings in your note book for class discussion.

    1. Cut off the top and bottom parts of the pumpkin. Name the top part North Pole and the bottom part South Pole.

    2. Use a thread and ruler to measure the circumference of the pumpkin. Record your findings.

    3. Measure the latitudinal distances around the pumpkin, 5 cm from each pole.

    4. Determine the middle part of the pumpkin and draw a line using a marker. This represents the equator. Measure its distance from the poles and note down your findings.

    5. From your findings, state the similarities and the differences between the two parts of the
    pumpkin.

    6. Use your findings to describe the shape of the earth.

    In the past, the shape of the earth was thought to be flat. Later on, scientific studies showed that it is almost spherical in shape.
    However, the shape of the earth does not make a perfect sphere. It is oblate spheroid or a geoid. It is flattened along the polar regions and bulges along the equator. It is therefore not an actual sphere.
    The dimensions of the Earth along the equator, the poles and the meridians give a hint about the shape of the Earth.

    Evidence to show that the shape of the Earth is not a perfect sphere

    (a) The polar diameter (12,722 km) is shorter than the equatorial diameter which stands at 12,762 kilometres.

    (b) The circumference of the polar and equatorial areas differ. The circumference at the equator is bigger than that at the polar regions.

    (c) There is great gravitational pull at the poles than at the equator. This is because areas along the equator are far from the centre of the Earth.

    (d) Modern satellites show that the Southern Hemisphere is slightly larger than the northern hemisphere.

    Evidence to show that the earth is not flat
    m
    Do this in pairs.
    1. Describe the shape of each of the following:
    (a) Eggs
    (b) Oranges
    (c) Watermelon
    (d) Football
    (e) A square wooden board
    2. Write down your points for a class discussion.
    3. Which one of the above items perfectly represent the shape of the earth?

    The above activity should help you prove that the shape of the Earth is spherical. The evidence listed below show that the Earth is not flat.
    (a) Aerial photographs taken using satellites from high altitudes show the earth is round.

    (b) The shadow cast onto the moon during the lunar eclipse shows the earth is round.
    (c) Several voyages taken around the earth have all proven that the earth is round. Movement on the earth along a straight path in one direction brings you to your starting point from the opposite direction.
    (d) Places on the Earth’s surface do not receive sunshine at the same time.
    (e) The sun keeps changing its altitude at different times of the day. In the morning and evening, the sun seems to be at a low altitude. At noon, the sun’s altitude is at a high altitude. This is illustrated below:
    n

           Fig 3.47 The sun at various altitudes.

    (f) The Earth’s horizon is curved. This is evidenced by approaching ships. The smoke, funnels and mast appear on the horizon, before the rest of the ship is seen from the coast.
    (g) The polar star looks bigger at the poles and smaller away from the poles.
    heart All the planets in the solar system are spherical. The Earth being one of the planets has a similar shape.

    The size of the earth
    Earth is the fifth largest planet in the solar system. It has a surface area of 510 million square kilometres. It is a member of the terrestrial planets and is the largest in the group. It is also the densest planetary body in the solar system. Table 3.2 shows the dimensions of the earth.

    Table 3.2 Dimensions of the earth.

    Measurement
    		 Kilometres
    Equatorial diameter

    		 12,762 km
    Equatorial circumference

    		 40,075.16 km
    Polar diameter
    		 12,722 km
    Meridional circumference

    		 40,009 km
    Surface area
    		 510,000,000 km2

    Position of the earth in the solar system

    As you earlier learnt, the Earth is the third planet in the solar system. It is about 150,000,000 million kilometres from the sun. It lies between Venus and Mars. It is the largest of the four terrestrial planets.

    b
    Do this in pairs.
    1. Using the Internet, encyclopaedias and other geography textbooks, describe other characteristics of the earth.
    2. Write down your findings in your notebook.
    3. Present your findings in a class discussion

    The Earth’s movements and their consequences

    There are mainly two types of the Earth movements.
    (a) Rotation of the Earth.
    (b) Revolution of the Earth.

    Rotation of the Earth on its axis
    n
    Do this in pairs. You will require an orange and a sharp stick. You can also use a globe if it is available.
    1. Hold the orange in your hand.
    2. Pierce the sharp stick through it. Ensure that the stick goes through both ends of the orange.
    3. Hold the stick with the orange on hand. Rotate it in a west to east direction.
    4. Compare this with the rotation of the earth on its axis.
    5. If you use a globe, rotate it to a west to east direction. Observe what happens.

    Definition of rotation

    Rotation is the act or process of turning around a centre or an axis. The earth is not static. It is always moving round its axis. The earth rotates in an anticlockwise direction from west to east. It rotates at a speed of 1680 kilometres per hour or 28 kilometres per minute.
    The earth’s axis is an imaginary line believed to cut across the centre of the earth. It cuts from the North Pole to the South Pole. The earth’s axis is inclined at 23° perpendicular to its orbital plane. The axis has two ends, namely:
    (a) North Pole
    (b) South Pole.

    m
            Fig 3.48 Rotation of the earth.
    The earth’s rotation takes 24 hours in which it is able to complete 360°. This means that
    for every 1° , the earth takes 4 minutes. This is calculated practically as shown below.
    360°=24 hours
    z
    Therefore, the Earth completes one degree in 4 minutes.
    b

    The consequences of the earth’s rotation

    The rotation of the earth has the following effects.
    (a) Day and night.
    (b) The rising and falling of ocean tides.
    (c) Differences in time between longitudes
    (d) The deflection of winds and ocean currents.
    (e) Variations in atmospheric pressure over the earth’s surface.
    (f) It influences the revolution of the moon round the earth.

    Day and night

    m
    You will require a torch and a ball or globe.
    1. One of you should hold the ball or globe and the other one the torch.
    2. The student with the lit torch should focus the light to one spot . You can focus it to the centre of the ball or globe.
    3. The student with the ball or globe should rotate the ball in a slow motion.
    4. Observe what happens and write it down.
    5. Present your findings in a class discussion.

    You will observe that the side of the ball facing the light is bright. The other parts facing away from the light are dark.
    v

    This is exactly what happens as the earth rotates.
    The side of the earth that faces the sun receives sunlight and thus experiences daytime. The opposite side of the Earth experiences darkness in the form of night.

    The rising and falling ocean tides

    A tide is defined as a rhythmic rise and fall of the sea level. This is caused by gravitational
    forces between the moon, the sun and the earth.

    When the earth is rotating, areas facing the sun are pulled by the sun’s gravitational force. However, the solid parts of the earth do not positively respond to this force. The mobile elements of the earth respond in particular the hydrosphere or water bodies. It influences the water levels causing sea levels to rise. When these specific areas move away from the sun, the sea levels go
    back to normal. These are referred to as solar tides.

    Parts of the earth that face the moon at night are subjected to the moon’s gravitational force. This causes lunar tides.
    At times, the moon and sun are aligned at the same position in a linear order. At such times, strong tides called spring tides are formed.
    The occurrence of tides can be observed at a shore. At high tide, the ocean water rises and covers most of the shore. At the low tide, the water flows back into the ocean. 
    Time differences between longitudes Longitudes are imaginary lines drawn on a map from the North Pole to the South Pole. They are geographic coordinates that specify the east–west position of a point on the earth’s surface. Longitudes are sometimes referred to as meridians. They
    are measured in degrees east or west of the Prime or Greenwich Meridian. This is a line that is marked 0° up to 180° both to the west and east.

    Longitudes are expressed in degrees. They cover 3600 of the globe. The difference
    between longitudes is 150 which is equivalent to 1 hour.
    The major longitudes are:
    (a) Prime or Greenwich Meridian
    (b) International Date Line.

    How to determine local time using longitudes

    The Prime Meridian is important in determining the local time. This is in reference to the usage of other longitudes. Calculation of time is in reference to Greenwich. Therefore, when calculating
    time away from the Greenwich Meridian, it is important to know the time at Greenwich.

    Example

    Calculate the time at Alexandria located
    at 30° east when the time at Greenwich is noon.

    Solution

    Step 1:

    Determine the difference in degrees between the two longitudes.
    The Prime Meridian and 30°.
    0° + 30°= 30° east.

    Step 2:

    Find the time based on the difference in degrees between the two longitudes. In this case, if the earth takes 360° to make a complete rotation in 24 hours, then:

     360°= 24 hours
    15° = 1 hour
    15°= 60 minutes
    1° = 4 times
    Therefore, 30° = 30° X 4 minutes
    =120 minutes
    Convert the 120 minutes into hours.
    1 hour = 60 minutes
    b

    Step 3:

    Alexandria is located east of Greenwich. This implies that the time there is ahead of that
    at Greenwich. Therefore;2 hours + time at Greenwich 
    2 hours +12:000 GMT =14:00 hrs (24 hour clock) or 2:00 p.m (12 hour clock)

    The time at Alexandra is 14:00 hrs (24-hour clock) or 2:00 p.m (12-hour clock) when it
    is noon at Greenwich.

    g
    Do this individually.
    Determine the time of various places using the longitudes given.
    (a) It is 2:00 pm at Greenwich, what is the time at Kinshasa which is located at 15° east?

    (b) It is 4:00 am at Greenwich; calculate the time at Mogadishu which is located at 45° east?

    The standard time and time zones

    The standard time
    This is the time recorded by all the countries found in the same geographical region. It is
    a time that is agreed by all the countries in a given region. For example, Uganda, Tanzania and Kenya have the same time. Standard time is important for the following reasons:
    (a) It helps in making schedules of transport systems.
    (b) It helps in creating schedules of meetings.
    (c) It gives a country a standard time that it is known for internationally

    Time zones
    A time zone is a region that observes a uniform standard time. This is important for legal, commercial, and social purposes. Time zones follow the boundaries of countries and their subdivisions. This is because it is convenient for areas close to each other to keep the same time.
    Each time zone is 15 degrees of longitude wide (with local variations). The local time is one hour earlier than the zone immediately to the east on the map. There are 24 time zones in the world.

    The International Date Line 

    As earlier discussed, the longitudes are measured from 0° (Greenwich) to 180° east or 1800 west. International Date Line refers to an imaginary line of longitude on the earth’s surface. It is located at about 180 degrees east (or west) of the Greenwich Meridian. It marks the change from one calendar day to the next. At any moment, there are two days on earth with the same time. A new day begins at midnight on the International Date Line. If one travels across the International Date Line, the date would change either forward or backward.

    At 12:00 a.m at Greenwich on Monday, it will be 12.00 a.m on Tuesday across the 180° east longitude. On the other hand, the time at 180° west would be 12:00 a.m on Sunday. In other words, time does not change; what changes is the date. When going to the east, one adjusts the clock by
    adding 24 hours to the time. When going west, one adjusts the time by subtracting 24 hours to the time.

    The deflection of winds and ocean currents

    The earth’s rotation from west to east results in winds and ocean currents changing direction. This change of direction is referred to as deflection. 
    Ocean currents are streams of water flowing in a horizontal direction. They are usually associated with seas and oceans.

            Maximum deflection at pole
    b
    Fig 3.50 Deflection of winds and ocean currents in the North and South Hemispheres.
    Winds and ocean currents change direction to the left in the Southern Hemisphere. They deflect to the right in the Northern Hemisphere.

    Variations in atmospheric pressure over the earth’s surface

    When the earth rotates, it causes the air at the poles to move towards the equator. As this air crosses latitudes that are becoming wider, it spreads out over a larger area. It creates low pressure at latitudes 60° north and south.

    Air moving from the equator towards the poles spreads over latitudes which are becoming shorter. As the surface area reduces, the air molecules contract hence having contact with each other. This builds high pressure at latitudes 30° north and south of the Equator. The earth rotates in an anticlockwise direction. It moves from west to east through 360° in 24 hours. In 1 hour, the earth covers 15°. To go through 1° it takes 4 minutes.

    The revolution of the moon round the earth
    c
    Do this in groups of three in the library. Use the Internet, encyclopedias and geography textbooks:
    1. Find out why the position of the sun keeps changing as the day progresses.
    2. Relate this to the rotation of the Earth on its axis.
    3. Write down your findings.
    4. Share your findings in a class discussion.

    The rotation of the Earth round the sun leads to the revolution of the moon round the earth. As the Earth rotates on its axis, it produces a centrifugal force which causes its satellite to move in a circular motion.
    This leads to revolution of the moon around the Earth.

    The revolution of the earth around the sun
    m

    1. Take a globe and rotate it to fully cover 360° in a west to east direction.
    2. Observe what happens.
    3. Compare this to the revolution of the earth round the sun.

    Definition of revolution
    Revolution refers to the motion of the earth on its orbit around the sun. The earth revolves round the sun from west to east.
    The earth takes one year or 365 ¼ days to complete its revolution round the sun. This happens in a normal year. A leap year occurs once after four years where the earth takes 366 days to complete one revolution. The earth is inclined at an angle of 66½°.

    The consequences of the earth’s revolution
    The earth’s revolution results in the following.
    (a) The occurrence of the four seasons.
    (b) Varying lengths of day and night.
    (c) Changes in the position of the overhead sun.
    n
                         Fig 3.51 Earth’s revolution round the sun.
    The four seasons
    b
    Do this in groups of four.
    (a) Analyse and discuss the climate of Rwanda.
    (b) Note down the rainy and dry periods.
    (c) How many climatic seasons does Rwanda experience?
    (d) If you lived in Europe, write down the seasons you are likely to experience

    Seasons are climatic changes that occur in different zones of the earth. They occur due to temperature changes that result from the earth’s position as it revolves around the sun. The earth’s axis is tilted at an angle of 66½°.
    This tilt brings about variations in the sunlight received at different latitude areas on earth. The revolution of the earth also brings variations in the sunlight received at different latitude areas. The seasons are mostly experienced in high and mid-latitude
    regions of the world. They are:

          (a) Summer                 (c) Winter
          (b) Autumn                  (d) Spring

    On 21st March, the sun is overhead at the equator. This time is the start of the spring season in the Northern Hemisphere. During the same period, it is autumn season in the Southern Hemisphere.
    On 21st June the sun is overhead at the tropic of cancer. This time is the start of summer in the Northern Hemisphere. During the same period, there is winter in the Southern Hemisphere.

    On 22nd December, the sun is at the overhead position at the tropic of Capricorn.
    This is summer time in the Southern Hemisphere and winter in the Northern Hemisphere.

    On 21st March and 23rd September the sun is overhead at the equator. During this period,
    days and nights are equal. This is called the equinox.
    The summer season is characterised by warm to hot temperatures because of the long durations of sunlight.
    The winter season is characterised by cool to cold temperatures because nights are longer.
    Spring and autumn are short seasons that mark the changes between winter and summer.
    The order of seasons is such that autumn comes before winter and spring before summer.
    The seasons determine the type of activities that take place at a given time. In winter for example, snow falls covering the ground making it frozen. People engage in indoor activities. Plants also remain dormant throughout winter. However, sports such as skiing and ice skating take place.

    Spring time comes immediately after winter. This is when temperatures begin to warm up springing everything back to life. Leaves sprout on trees, grass and flowers begin to grow and hibernating animals become active.
    The summer season which follows spring is full of activities. Plants and animals become active. Fruits and grains mature and ripen for harvest before autumn sets in.
    In autumn, plants begin to shed their leaves and animals begin to hibernate in preparation for winter.
    These four seasons occur in the temperate zones. These are the regions between the
    tropics and the Arctic and Antarctic circles.
    m
            Fig 3.52 The four climatic seasons in the Northern and Southern Hemispheres.

    Table 3.2: Description of seasons

    Season
    		 Description
    Winter
    		 • Very low temperatures
    • Severe cold
    • Land mostly covered by snow in some areas
    Spring
    		 • Occurs after winter
    • Temperatures begin to increase leading to summer
    conditions
    Summer
    		 • A lot of sunshine
    • High temperatures
    Autumn or Fall
    		 • Occurs when summer is ending
    • Temperatures start falling and decreasing towards very cold
    conditions

    Task 3.4
    1. What is the meaning of the term season?
    2. Name the seasons experienced in Europe.
    3. On which date(s) is the sun overhead the equator?
    4. Mention the date(s) when the sun is overhead at the Tropic of Cancer and Tropic of Capricorn.
    5. Explain the meaning of equinox.
    The varying lengths of days and nights
    The earth’s revolution leads to differences in the lengths of days and nights. During summer, longer hours of sunshine are experienced. Longer hours of darkness are experienced during winter . This means that in summer there are more days of sunshine than darkness. It also means that in winter,
    there are more days of darkness than days of sunshine.

    For example, in December, hours of darkness increase in the Northern Hemisphere. At the same time in the Southern Hemisphere, hours of sunshine increase. As one goes beyond the Arctic circle 66° north, there are days of total darkness.

    Changes in the position of the overhead sun

    The sun’s altitude is the height of the sun above its nearest horizon. The sun changes its altitude in relation to the earth’s revolution as seen in Figure 3.52.
    b
               Fig 3.53 Changes in the position of the overhead sun.
    Task 3.5
    1. List and explain the effects of the earth’s revolution round the sun.
    2. Define the following terms:
       (a) axis           (b) tides.
    3. What is the difference between standard time and time zone?
    4. Give the meaning of International Date Line.
    5. What are ocean currents?
    6. Differentiate between the earth’s revolution and earth’s rotation.
    7. State and examine the effects of the earth’s revolution

    Latitudes and longitudes
    m
    Do this in pairs.
    You will require a globe or a ball, thread of different colours and a ruler.
    1. Tie a red thread round the globe or ball. The thread should run vertically from the top to the bottom.
    2. Make 24 other vertical runs of thread of different colours round the globe or ball. Ensure that the space between one thread and the next is equal. Use a ruler to obtain exact measurement. You can use sellotape or glue to ensure that the threads stick in place.

    3. Get a strand of the red thread that you had used before. Determine the centre of the ball or globe using the ruler. Tie the thread horizontally across the ball or globe.
    4. Use threads of a different colours and pass them horizontally round the globe. Ensure that the spacing between one thread to the other is equal. Use the ruler to ensure this. You can use sellotape or glue to ensure that the threads stick in place.
    5. Differentiate between the vertical and the horizontal threads.
    Latitude
    A latitudes is the angular distance of a place north or south of the earth’s equator Latitudes range from 0° at the equator to 90° north or south at the poles. They are measured in degrees, minutes and seconds north or south of the equator. On a map, latitudes are drawn horizontally from west
    to east. Lines of latitudes are referred to as parallels.
    Distance between lines
    The distance on the earth’s surface for each degree of latitude or longitude is about 111 kilometres. This is achieved if you divide the circumference of the earth by 360°.
    It is important to note that this distance reduces as you move towards the poles.This is the direction towards north or south of the equator.
    g
              Fig 3.54 A map of the Great Lakes countries showing latitudes and longitudes.
    Longitude
    A longitudes is the angular distance of a place east or west of the Greenwich Meridian. Longitudes are measured in degrees, minutes and seconds east or west of the Greenwich Meridian. They
    are imaginary lines drawn on a map, from north to south. Lines of longitudes are also referred to as meridians. They help us to determine the time of a given place and locations of different places.
    Latitudes and longitudes are used together on a map. They help in finding the exact locations of places and features easily. In Activity 3.33 on page 88, the vertical threads that you tied on the globe represent the longitudes. The red middle thread represents the Greenwich Meridian which
    is a very important longitude.
    The horizontal threads that you tied represent the latitudes. The red thread that you tied across the globe or ball represents the equator. The equator is a very important latitude. When reading the coordinates on a map, remember the following tips.
    • Latitude is always given before longitude (49° N 100° E).
    • Latitudes are parallel, but longitudes are not.
    • Degrees west and south are sometimes referred to as negative degrees (–12° –23° is the same as 12°S 23°W).
    • The latitude of a place affects its climate, but its longitude does not.
    • Key longitude lines are the Prime Meridian (0°) and the International Date Line (180°).
    • Key latitude lines include the Equator (0°), Tropic of Cancer (23° 26’ N), Tropic of Capricorn (23° 26’ S), the Arctic Circle (66° 33’ N) and the Antarctic Circle (66° 33’ S).
    m
    Use an atlas to do the following.
    1. Distinguish between latitudes and longitudes.
    2. Find the location of Kigali City on a map of Rwanda using latitudes and longitudes.
    3. Determine the coordinates of the location where you were born on a map of Rwanda.
    4. Find the location of Kigali City on a world map using latitudes and longitudes.
    5. Present your work to your teacher.

    Earlier in this unit, you learnt that the rotation of the earth causes differences in time between longitudes. You learnt how to determine time using given longitudes. This is in relation to the Greenwich Meridian.
    In this sub-topic, you will learn how to determine the longitudes of different places. This is done using time in relation to the Greenwich Meridian.
    How to determine the longitude of a place using time

    It is also possible to determine the longitude of a given place using time.
    d
    Do this individually. Make reference to a globe, a map or an atlas.
    1. Determine the longitude of Taipei in Taiwan whose local time is 8:00 p.m when the local time in London is 12 noon.
    2. What is the longitude of Nairobi whose local time is 8:00 a.m, when it is 5:56 a.m in Accra?
    3. Mr. Kamari took a flight from London at 12 noon to Honiara Island that is located at 159°E. What time did he arrive at Honiara?
    4. It is noon at Manaus in Brazil which is situated at 60°W. What would be the
    time in Dhaka located at 90°E?
    This is done in reference to the time at Greenwich and the specific area. Study the
    example shown below.
    Example
    Calculate the longitude of place X whose local time is 10:00 p.m when the local time
    at Greenwich is 1:00 p.m.
    Step 1:
    Find the difference in time between two longitudes.
    Time at Greenwich is 1:00 p.m.
    Time at location X is 10:00 p.m
    1:00 p. m - 10:00 p. m = 9 hours
    Step 2:
    For every hour, the earth rotates through 15°. Therefore, in 9 hours the earth will have
    rotated through 15 × 9 =135°
    Step 3:
    The time at Greenwich is behind that of location X. This means that location X is east
    of Greenwich by 135°. Therefore location X is 135° east of Greenwich.

    Did you know?
    • A huge part of the universe is made up of things we cannot see.
    • The solar system was formed approximately 4.6 billion years ago.
    • The formation of the solar system was by the collapse of a giant cloud.
    • 99.86% of the solar system’s mass is found in the sun.
    • A person would weigh much less on the moon than on earth.
    b
    1. (a) What is the universe?
    (b) List the components of the universe.
    2. Using examples, distinguish between a constellation and a galaxy.
    3. Describe the composition of the solar system.
    4. List four characteristics of the moon.
    5. (a) Name two earth movements.
        (b) Discuss the consequences of the rotation of the earth.
        (c) Discuss the consequences of the revolution of the Earth.
    6. Distinguish between a latitude and a longitude.
    7. With the use of well-labelled diagrams, describe the main types of eclipse.



    Planet
    		Key features
    Mercury
    		• It is the smallest planet.
    • It is the nearest planet to the sun.
    • It completes its revolution in 88 days.
    • It is moonless.
    • It is about 70 million kilometres from the sun when it is at its farthest.
    When it is closest to the sun , it is at 47 million kilometres away.
    Venus
    		• It is slightly smaller than planet earth.
    • It is one of the brightest planets in the universe.
    • It is almost similar to the earth.
    • It is moonless.
    • It is 108.9 million kilometres from the sun.
    • It takes 225 days or 0.165 Earth years to complete its revolution
    around the sun.
    Earth
    		• It is the third planet from the sun.
    • It is the only planet known to support life .
    • It is 146 million kilometres from the sun.
    • It has one moon.
    • It takes 365 days to complete a revolution around the sun.
    Mars
    		• It is slightly cooler than other planets.
    • It is 228 million kilometres from the sun.
    • It has 2 moons.
    • It takes 686.971 Earth days to complete a revolution around the sun.
    Jupiter
    		• It is the largest planet.
    • It has 63 moons.
    • It takes 12 Earth years to complete one revolution round the sun.
    • It is 779 million kilometres from the sun.
    Saturn
    		• It has a ring around it making it unique.
    • It has 62 moons.
    • It is 1.4 billion kilometres from the sun.
    • It takes 29.4 Earth years to complete a revolution around the sun.
    Uranus
    		• It is the 7th planet in the universe .
    • It is the 8th 2.5 billion kilometres from the sun.
    • It has 27 moons.
    • It takes 84.3 years to complete a revolution around the sun.
     Neptune • It is the 8th planet from the sun.
    • It is 4.5 billion kilometres from the sun.
    • It has 13 moons.
    • It takes 164.79 Earth years to complete a revolution around the sun.