By the end of the topic, the learner should be able to:

1. define the solar system
2. explain the origin of the earth
3. explain the effects of rotation and revolution of the earth
4. Describe the structure of the earth.

1. Definition and composition of the solar system
2. Origin, shape, size and position of the earth in the solar system
3. Rotation and revolution of the earth and their effects
4. Structure of the earth
   1. The atmosphere
   2. The hydrosphere
   3. The lithosphere/crust
   4. The asthenosphere/mantle
   5. The barysphere/centrosphere (outer and inner core)

Solar system is the group of heavenly bodies comprising the sun and the nine planets.
The origin of the Solar System
Theories
A theory is a set of reasoned ideas intended to explain facts or events
1. Passing Star Theory
A star with a greater gravitational pull passed near the sun, it attracted large quantities of gaseous materials from the sun, and the materials split, cooled and condensed to form planets, the planets were set in orbit by the passing star
Weaknesses

1. Doesn’t explain the origin of the sun and star.
2. Minimal chance of a star approaching another
3. High temperature, gaseous material drawn from the sun would disperse than condense
4. The gases should have followed the star since it had a greater gravitational pull

2. Nebula Cloud Theory
There was a slowly rotating cloud of dust and gas called Nebula, As the nebula rotated it flattened into a disc with high concentration of materials at the centre, The high concentration of material at the centre condensed to form the sun. Gases such as ammonia and methane condense to form larger planets that is Jupiter, Saturn, uranius and Neptune. Closer to the centre of Nebula, particles of dust and gas bumping into each other formed the inner smaller planets.
Evidence
Rotation and revolution of planets in anticlockwise direction
Weakness

1. The origin of nebular is not explained.
2. Cause of rotation is not mentioned.
3. All planet should rotate in the direction of the rotation of the nebula that is west to east but Venus and uranius rotates from west to east.

3. Collision Theory
Star with greater gravitational pull passed near the sun. It attracted large quantities of gaseous materials. The materials split into portions. Large portions collided with smaller ones and swept them to form planets. The weaknesses are the same as the passing star’s Theory.
4. Supernova/explosion Theory
There was a violent explosion of a star. A cloud of dust (nebular) remained from the star. There was fast movement of the cloud due to the force of explosion. Rotation speed increased due to gravitational attraction. The cloud flattened into a disc. The matter began to accumulate towards the centre to form a proto-sun which later began to shine. The rest of the cloud collapsed to form planets.
Weaknesses

1. Doesn’t explain the origin of the star
2. Doesn’t explain the cause of explosion

1.   The Sun
It’s the centre of the universe.
Characteristics

• It’s a star - A star is a heavenly possessing its own light which it transmits.
• Nebula/galaxy is a cluster of stars.
• The earth is in a galaxy called The Milky Way.
• It’s made of very hot gases mainly hydrogen (70%) and helium (30%).
• Has a diameter of 1,392,000km.
• Surrounded by a layer of gas which has boiled from its surface which is called corona.
• Rotates on its own axis in anticlockwise direction.
• Has gravitational pull which holds all the planets in orbit around it.
• An orbit is a path which a planet or a satellite follows around a star or a planet.
• Temperature at its centre is 15m◦c and at the surface is 5500◦c.
• Radiates solar energy which is very important for all forms of life on the earth.

2.   The Planets
Planets are large spherical celestial/heavenly bodies in space.
There are 9 planets in our solar system.
Characteristics

• Spherical in shape
• Don’t have their own light but reflect it from the sun.
• Revolve around the sun in anticlockwise direction.
• Have their own force of gravity
• Only one is known to support life.
• The following are the planets arranged in order from the one nearest to the sun.

a) Mercury

• Nearest from the sun
• Its 58m km from the sun
• Has no satellites
• Takes approximately 88 earth days to revolve around the sun

b) Venus

• 2nd planet from the sun
• It’s 108m km from the sun
• One of the brightest planets
• Can be seen clearly with naked eyes
• Takes approximately 225 earth days to revolve around the sun
• Slightly smaller than the earth
• Has no satellites
• Together with the earth they are called twin planets due to having many similarities

c) Earth

• The 3rd planet from the sun
• The earth and the heavenly bodies make the universe
• The only planet that supports life
• The home of man
• Approximately 149m km from the sun
• Takes 365 ¼ days to revolve around the sun
• Has one satellite, the moon

a) Mars

• Also called The Red Planet because when it’s observed through a telescope it appears reddish.
• The 4th from the sun
• Slightly smaller than the earth
• Approximately 228m km from the sun
• Takes 687 earth days to revolve around the sun
• Between Mass and Jupiter there are small celestial bodies called planetoids.
• Has no satellite.

b) Jupiter

• 5th planet from the sun
• Approximately 778m km from the sun
• Largest in the universe
• Rotates on its own axis at very fast speed
• Has flattened poles due to its fast speed of rotation
• Has very thick layers of ice on its surface takes 12 earth years to revolve around the sun
• Has 16 satellites

c) Saturn

• 6th planet from the sun
• Second largest planet
• Approximately 1427m km from the sun
• Takes 29 ½ earth years to revolve around the sun
• Has a ring around it
• Has 18 satellites

d) Uranus

• 7th planet from the sun
• About 4 times bigger than the earth
• Approximately 2870m km from the sun
• Also rotates very fast
• Also has flattened poles due to fast speed of rotation
• It appears greenish foe being surrounded by methane gas
• Has 8 satellites
• Takes 84 earth years to revolve around the sun

 e) Neptune

• One of the farthest from the sun
• 8th planet from the sun
• Approximately 4497m km from the sun
• Has 8 satellites
• Takes 165 earth years to revolve around the sun
• Very similar in size, colour and character with Uranus

f) Pluto

• 9th planet from the earth
• Farthest from the sun
• The smallest
• 1/6 the size of the earth
• Approximately 5900m km from
• Takes 248 earth years to revolve
• Has one satellite
• Very little is known about it

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KCSE Topical Questions

• ANSWERS
• QUESTIONS

Classroom Questions on Topic

By end of this topic, the learner should be able to:

1. Define the terms Geography and Environment.
2. Describe the branches of Geography
3. Explain the importance of studying Geography.
4. Explain the relationship between Geography and ​other disciplines

Definition of:

1. Geography
2. Environment

Branches of Geography

1. Physical Geography
2. Human Geography

Importance of studying Geography
Relationship between Geography and other disciplines

1. Scientific study of the earth as a home of man.
2. Study of interrelationship on natural and human phenomena on the earth’s surface.

1. The surroundings
2. All external conditions surrounding an organism which has influence over its behaviour.Environment can be divided into two:

The Physical Environment

• Natural physical conditions of weather, climate, vegetation, animals, soil, landforms and drainage.

 
The Human Environment

• Human activities such as farming, forestry, mining, tourism, settlement, transportation, trade and industry.

1. Physical Geography
Deals with the study of natural physical environment of human kind.
The areas covered include:

1. Geology - study of the origin, structure and composition of the earth. It includes study of rocks.
2. Geomorphology - the study of internal and external land forming processes and landforms.
3. Climatology - the study of climate and weather
4. Pedology - the study of soils
5. Biogeography - the study of soils, vegetation and animals.
6. Hydrology- the study of water bodies
7. Spatial geography -study of space

2. Human and Economic Geography
Study of people and their activities on the earth’s surface.
The areas covered include:

1. Mining
2. Forestry
3. Agriculture
4. Fishing
5. Wildlife and tourism
6. Industry
7. Energy etc.

3. Practical Geography
A smaller branch which equips the learner with practical skills that enhance their understanding and interpretation of human and physical geographical information.
The areas are:

1. Statistical methods
2. Map work
3. Field work
4. Photograph work

1. Facilitates good relationship among nations by studying geography of other regions of the world.
2. it’s a career subject in that it enables one to go for advanced studies in specialised fields e.g. geography teachers, meteorology, surveying etc.
3. Enables us to appreciate other people’s way of life by learning economic activities of different communities within our country and other parts of the world.
4. Enables us to conserve our environment when we learn negative and positive effects of human activities on the environment.
5. Enables us to conserve our resources when we learn wise use of resources in conservation and management of resources e.g. wildlife, forests, energy, etc.
6. Inculcates in us virtues of cooperation and patience as we work in groups.
7. Makes us to appreciate manual work as we are involved in practical geography which may lead to self-employment.
8. Promotion of industry such as tourism by guiding tourists to places of interest by using maps, calculations of distances etc.

1. Mathematics-mathematical techniques are used in drawing graphs and pie charts and mathematical formulae are used in geography to calculate distances, areas, population density, population densities, etc.
2. History-history uses geographical tools like maps, charts and graphs to show where past events took place e.g. the movement of people in the past.
3. Biology-Geography explains the distribution of organisms and factors influencing their distribution on the earth’s surface.
4. Physics-geography uses physics principles and formulae to calculate and describe aspects such as magnetic field, gravity, vibrations of the earth etc.
5. Chemistry-geography applies chemistry in studying chemical composition and chemical changes which take place in soils and rocks.
6. Agriculture-geography studies farming systems, their distribution and factors affecting farming activities.
7. Meteorology-geography uses meteorological information in the study of weather and in classifying climatic regions and mapping them.
8. Geology-geography studies rocks.

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1. Describe how Geography is related to the following subjects:
   1. Mathematics
   2. Physics
   3. Agriculture
   4. Chemistry
   5. Biology
2. What is Geography?
3. Name three branches of Geography giving three examples in each branch.
4. Define the term environment.
5. Explain five reasons why people study Geography.
6. Distinguish between habitat and environment
7. State three areas where Geography is applicable and how it is applicable.