204-10-1.pdf

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Billie Call Christian Institute
1st marking Period Lecture Notes
Grade 10 Geography
The Solar System
THE STRUCTURE OF THE EARTH
The structure of the earth is grouped into two zones. These are the outer structure and the internal structure.
The earth Square miles/miles Square kilometers/km
Total area 196, 672, 000 509, 450, 000
Land area 57, 688, 000 149, 450, 000
Water 138, 987, 000 360, 000, 000
Equatorial circumference 24, 902 miles 40, 075 km
Equatorial diameter 7, 926 miles 12, 756 km
THE OUTER STRUCTURE OF THE EARTH
The outer structure of the earth is made up of four zones or layers. These zones or layers are:
(i) Lithosphere
(ii) Hydrosphere
(iii) Atmosphere
(iv) Biosphere
(a) Lithosphere
Characteristics of Lithosphere
(i) The lithosphere is the solid portion of the earth.
(i) It is the outermost layer or zone of the earth’s crust.
(ii) It is made up of rocks and mineral materials.
(iii)It represents 30% of the earth’s surface.
(iv)It forms the land mass which is about 10-50 km thick.
(v) The outermost layer of the land mass is made up of loose rock materials like gravel, sand, and soils.
Importance of Lithosphere to Man
i. The lithosphere forms the basis of all human settlement.
ii. All mineral resources are derived from the lithosphere.
iii. It aids transportation through the construction of roads, airports airport, etc.
iv. All farming activities are carried out on the lithosphere.
v. Most human activities like mining, trading, etc. are carried out on the lithosphere.

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(b) Hydrosphere
Characteristics of Hydrosphere
(i). The hydrosphere is the liquid portion of the earth.
(ii). It covers about 70% or 2
3
⁄ of the earth’s crust.
(iii). It holds water in various forms-solid e.g., Ice, liquid-like water as gases e.g., Water vapor.
(iv). It includes all forms of fresh water like lakes, rivers, and vapor.
(v). It also includes ocean water which is salty.
(vi). Ocean water accounts for about 97% of the hydrosphere.
Importance of Hydrosphere to Man
(i). Hydrosphere provides water for domestic uses e.g. washing, drinking, cooking, etc.
(ii). It provides a medium of transportation.
(iii). It also provides water for industrial uses.
(iv). It provides food in form of fish, prawns, etc. to man.
(v). It provides employment e.g. fishermen.
(vi). It’s a medium for sports e.g. swimming, diving, etc.
(vii). It can also be used to generate electricity e.g. hydro-electric power.
(viii). It is used in agriculture in form of rain or irrigation.
(ix). It also serves as a tourist center e.g. rivers and beaches.
(c) Atmosphere
Characteristics of Atmosphere
(i). The atmosphere is the gaseous portion of the earth.
(ii). It is a layer of gases surrounding the earth.
(iii). Over 9% lies within 30km of the earth’s surface.
(iv). Its density decreases progressively with elevation.
(v). It contains water in form of vapor in lower layers.
(vi). Weather phenomenon-cloud, rain, and snow-are largely confined in the atmosphere.
(vii). It contains 78% Nitrogen, 21% Oxygen, 0.03% Carbon dioxide and 0.97% rare or inert gases.
Importance of Atmosphere to Man.
(i). The atmosphere is the habitat of some living organisms.
(ii). It provides oxygen for animals and plants for respiration.
(iii). It provides carbon dioxide for photosynthesis by plants.
(iv). It provides oxygen for combustion or burning.
(v). It provides nitrogen for plants (protein synthesis).
(vi). It acts as a greenhouse gas.
(vii). Atmosphere is a medium of communication e.g., air routes.
(viii). It contains no ozone layer which acts as a
protective cover for living organisms against the
burning effects of ultra-violet rays of the sun.
(d) Biosphere
Characteristics of Biosphere
(i). The Biosphere is the zone of the earth occupied
by living organisms.
(ii). It is a layer where life exists on the earth’s
surface and the lithosphere.

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(iv). It is a narrow zone where complex biological and chemical activities occur.
(v). It includes organisms like plants, animals, and microorganisms.
Importance of biosphere to Man
(i). Plants in the biosphere provide food for man.
(ii). It also provides a source of energy like firewood for man.
(iii). Plants also provide clothing materials like cotton and wool for men.
(iv). It provides shelter in form of timber for man.
(v). It provides raw materials like timber, hides and skin, and cotton for industries.
(vi). Activities within the biosphere provide employment for man.
(vii). It aids the balancing and purification of atmospheric gases e.g. Carbon dioxide during respiration and
oxygen, during photosynthesis.
INTERACTION WITHIN AND BETWEEN THE FOUR ZONES
(a). Within the Lithosphere
(i). The rocks withers to form the soil.
(ii). The rocks also change to minerals like coal, petroleum, gold, etc.
(b). Within the hydrosphere
(i). Water from seas and oceans evaporates to form clouds and rainfall.
(ii). Water from rivers, streams, and rainfall combine to form the water in seas and oceans.
(c). Within the Atmosphere
(i). Water vapor combines to form clouds and rain.
(ii). Oxygen is taken in by plants and animals to release carbon dioxide.
(iii). Carbon dioxide is taken in by plants to release oxygen.
(d). Within the Biosphere
(i). Animals depend on plants for their food.
(ii). The decomposition of animals provides manure for plants.
(iii). Microorganisms in the soil promote plant growth.
(iv). Animals provide carbon dioxide for plants during respiration.
(v). Plants provide oxygen for animals during photosynthesis.
Interactions Between the Four Zones
(i). Plants and animals can be found in the lithosphere, atmosphere, and hydrosphere.
(ii). Plants in the biosphere derive their nutrients from the soil (lithosphere).
(iii). Most human activities are mainly carried out in the lithosphere.
(iv). Gases like oxygen and carbon dioxide are made constant in the atmosphere through respiration and
photosynthesis.
(v). Sunlight from the atmosphere is required by plants to carry out photosynthesis.
(vi). Atmosphere contains water vapor from the hydrosphere.
THE INTERNAL STRUCTURE OF THE EARTH
The internal or inner structure of the earth is made up of three
concentric layers which are:
(i). Crust (Lithosphere),
(ii). Mantle (Mesosphere) and
(iii). Core (Barysphere)

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(1). The Crust or Lithosphere Characteristics
The crust is subdivided into upper and lower parts.
(i). The upper part of the earth’s crust consists of granite rocks and forms the continent.
- The main minerals here are silica and aluminum, collectively referred to as sial
- The upper earth crust has an average density of 27.
(ii). The lower part of the earth’s crust consists of basalt rocks and forms the ocean floor.
- It contains minerals like silica, iron, and magnesium collectively referred to as sima,
- The lower crust has a density of 3.0.
- The sial, therefore, is lighter than the sima.
- The sial and sima are 5-6km below the ocean and 48km below the surface of the continent.
- The lithosphere lies above the mantle
- It forms the soil and sustains life.
-
(2). The Mantle or Mesosphere Characteristics
- The mantle is found just beneath the crust.
- It is about 2897km thick.
- It is very dense.
- Its main mineral is olivine.
- It is in plastic and in semi-liquid form.
- Has an average density of about 3.3.
- It is a middle layer that surrounds the core.
(3). The Core or Barysphere Characteristics
- The core is the innermost part of the earth.
- It is about 3476km in radius or width all around.
- It contains two minerals – iron and nickel, collectively referred to as nife.
- The temperature of the core is estimated to be as high as 2000o
c (3500OF
).
- The core is also subjected to constant temperature and pressure.
- It is in a molten state.
- The correct arrangement of the layers of the earth’s crust from the surface to the interior is sial, sima,
mantle, and cone.
STUDY QUESTIONS
1. (a) Name the zones in the outer structure of the earth.
(b) Briefly discuss the importance of two of the zones.
2. With the aid of a well-labeled diagram, describe the structure of the earth.
3. (a) Name the main sources of water in the hydrosphere.
(b) Lost five importance of the hydrosphere to man.
4. (a) Briefly describe the interaction within each zone of the outer part of the earth.
(b) List four possible interactions between the four zones.
5. (a) Describe the main characteristics of each of the following: (i)atmosphere (ii) hydrosphere (iii)bio-
sphere.
(b) Highlight the importance of the atmosphere to living organisms.
6. Draw a well-labeled diagram to show the internal structure of the earth. (ii) Describe the distinguishing
characteristics of any one of the layers shown in your diagram.
(b) Outline the importance of either the hydrosphere or the biosphere to man.
7. Draw a well-labeled diagram to show the internal structure of the earth. (b) Describe the main features of
the two of the parts shown in 7(a) above.

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The Solar System
The solar system consists of the sun and the nine planets with their satellites. (Fig. 3.1)
The nine planets are:
1. Mercury
2. Venus
3. Earth
4. Mars
5. Jupiter
6. Saturn
7. Uranus
8. Neptune
9. Pluto
All nine planets revolve around the sun in elliptical orbits. The path followed by each planet around the
sun is known as its orbit.
• A satellite is a smaller body that moves around the planet, e.g. the moon is the natural satellite of
the earth.
THE SUN
- The Sun is in the center of the planets. It does not in itself move.
- It is stationary while all the planets move around it.
- The Sun is the largest star and has a surface temperature of 6000o
c.
- It is the ultimate source of light and energy to all the planets.
- The planets shine only by the reflected light of the sun.
- The stars which appear singly when viewed from the earth exist in
groups or clusters which are better described as galaxies or nebulas.
THE PLANETS AND THEIR CHARACTERISTICS
The nine planets with their characteristics are discussed as follows:
1. Mercury
- Mercury is the smallest, the hottest, and the closest planet to the sun.
- It contains no living thing because it has the highest surface temperature.
- It takes eight-eight days for mercury to complete its orbit.
- It has the shortest orbit around the sun.
- It distances from the sun is 57,600,000km (36,000,000 miles).
- It has no satellite.
- It has a diameter of 4,800 km.
2. Venus
- Venus is the second closest planet to the sun.
- It also contains no living things
- It is often regarded as the “earth twin” because of its proximity in size, mass, and density.
- It takes Venus 225 days to complete its revolution.
- Its distance from the sun is 107,200,000 km.
- It has no satellite
3. Earth
This is the only planet that supports the existence of plants and animals.

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It has one natural satellite called the Moon which revolves eastward around the earth once in every twenty-
seven days.
It takes 3651
4
⁄ days (a year) to complete its orbit.
The distance between the sun and the earth is 148,629 km.
It has a diameter of 12,762 km.
4. Mars
- Mars is believed to be the next planet after earth to have the possibility of supporting some plants’ life.
- It has two satellites.
- It distance from the sun is 227,200,000 km.
- It takes Mars 687 days to complete its orbit.
5. Jupiter
- Jupiter is the largest planet in the solar system.
- Its surface contains gases such as hydrogen and methane with light and dark bands.
- It has twelve satellites.
- Its distance from the sun is 772,800,000 km.
- It takes Jupiter about 11.9 years to completer its orbit around the sun.
6. Saturn
- Saturn is the second largest planet after Jupiter.
- It has three rings.
- Its distance from the sun is 1,417,600,000km.
- It takes Saturn 29.5 years to complete its orbit.
- It has nine satellites
- It has a diameter of 119,700km.
7. Uranus
- Uranus’ orbit, unlike other planets around the sun, is in a clockwise direction from east to west.
- It has five satellites that revolve around it.
- Its distance from the sun is 2,854,400,000km.
- It takes Uranus 84 years to complete its orbit.
- It has a diameter of 51,000km.
8. Neptune
2) Neptune is very cold.
3) Its distance from the sun is 4,468,800,000km.
4) It takes about 164.8 years to complete orbit.
5) It has two satellites.
6) It has a diameter of 45,000km.
9. Pluto
7) Pluto is the coldest and farthest planet from the sun.
8) It has the longest orbit around the sun.
9) It takes about 247.7 years to complete its orbit.
10) Its distance from the sun is about 5,850,000,000km.
11) It has no satellite.

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12) It has a diameter of 5,800km.
THE MOON
The moon is the only satellite of the earth. It is often seen at night to be the largest and the brightest object
in the sky. It has no light of its own but shines by reflecting the light from the sun. As a result of this, only
half of the moon that faces the sun is lit up. The moon revolves (or moves around) the earth once in every
28 days.
In the same period, it completes one rotation on its axis. Therefore, the same side of the moon is always
facing the earth. There is no air or water on the moon. As a result of this, the moon is very hot (about
120o
c) when heated by the sun and very cold about −180o
C when it is not. The surface of the moon is
made up of mountains, crates, and dry plains. Because the moon does not contain as much material as the
earth, its gravitational pull is less. A person who weighs 70kg on earth will weigh only about 20kg on the
moon. That is why a man can leap to a much greater height on the moon than on the earth. The moon’s
diameter of 3,500km is one-quarter that of the earth. It is about 384,000km away from the earth.
Many people have traveled to the moon from different locations and at different times. Neil Armstrong was
the first man to land on the moon on the 21st
of July, 1969. He traveled there in the company of two other
American astronauts Aldrin and Collins.
Study Questions
1. a) What is Solar System?
b) Name the first four planets and describe their characteristics.
2. a) What is an elliptical orbit?
b) Discuss in detail three planets in the solar system.
3. a) Name three planets that have no satellites.
b) Describe the characteristics of the hottest and the coldest planets in the solar system.
4. a) Describe the solar system.
b) Outline four characteristics of each of the following planets:
Earth, Mars, Jupiter, and Saturn
5. Write short notes on:
a) The sun
b) The Moon
THE EARTH AS A PLANET
The Shape and Size of the Earth
The Shape of the Earth
The earth is not flat but has a spherical shape. It is slightly flattened at the poles to give a nearly spherical
shape; hence the earth’s shape is better described as a geoid which means, the earth’s shape.

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THE Size of the Earth
The earth is the fifth largest planet in the solar system. The surface area of the earth is approximately 443
million square kilometers (197 million square miles). Other important dimensions of the earth are:
1. Equatorial circumference=40,085km
2. Equatorial diameter=12,762km
3. Polar circumference = 39,955𝑘𝑚
4. Polar diameter = 12,722𝑘𝑚
EVIDENCE/PROOF OF THE EARTH’S SPHERICITY
There are many ways to prove or show that the earth is spherical. These include:
1. Circumnavigation of the Earth: it is possible to go round the earth by air, land, and, sea and
return to the starting point as carried out by Ferdinand Magellan and his crew between 1519
and 1522. If the earth is flat, one would come in contact with an abrupt edge and fall off.
2. Sunrise and Sunset: as the earth rotates from west to east, places in the east experience the sun
earlier (sunrise) than places in the west. Also, places in the west see the sun later (sunset) than
places in the east. The whole earth would experience sunrise and sunset at the same time if the
earth is flat.
3. The Circular horizon: when one views a distant horizon from any point of the earth, the shape
is always circular. And as one climbs higher, the circular horizon widens. This type of feature
is seen only on a spherical body.
4. Ship’s visibility: when a ship approaching a port is viewed, the top of the mast is seen first
before the hull and later the rest of the ship’s body. In the same way, if a ship leaves a harbor, it
disappears gradually. If the earth is flat, the ship from a distant view would appear and
disappear at once.
5. Planetary bodies: when the sun, moon, stars, and other planetary bodies are viewed from any
angle, they are all circular in outline. So, the earth cannot be an exception.
6. Driving poles of equal length on the Earth: three poles of equal length driven at the same
depth on the level ground were found to have the center pole projected slightly above the poles
on either side because of the curvature of the earth. If the earth is flat, all the poles would have
the same height.
7. The Lunar eclipse: During a lunar eclipse, the earth casts a circular shadow on the moon.
Only a sphere, like the earth, can cast such a circular shadow. The earth comes between the sun
and the moon and the shadow cast on the Earth is circular.
EARTH’S MOVEMENT (ROTATION AND EFFECTS)
The earth moves in space in two different ways. These are:
a. Rotation;
b. Revolution.
Rotation of the Earth
Definition
Rotation of the earth is defined as the movement of the earth around the sun on its axis.
- The earth moves or rotates on its axis from west to east.
- The rotating earth is inclined at an angle of 23
1
3
o
along its axis.

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- It takes the earth twenty-four hours (i.e. a day) to complete one rotation (i.e. the earth rotates through
360o
every 24 hours).
- The rotation of the earth causes day and night.
- This is why it is said that there are twenty-four hours in a day. That is twelve hours of daylight and
twelve hours of darkness. However, this division does not occur at all times in all places.
- It rotates through 51o
in 2 hours of 1o
in 4 minutes.
➢ Effects of Rotation of the Earth.
1. Day and Night: as the earth rotates, only one part of the earth’s surface facing the sun receives the rays of
the sun and experiences daylight (day) while the other part of the earth backing the sun’s rays will
experience darkness (night).
2. Deflection of winds and ocean current: the rotation of the earth causes winds and ocean current to be
deflected to the right of the direction in which they move in the Northern hemisphere and, to the left of
this direction in the Southern hemisphere;
3. Apparent sunrise and sunset: during the rotation of the earth, part of the earth that emerges from the
darkness into the rays of the sun experiences sunrise while the part that is moving away from the sun’s
rays to darkness will experience the sunset.
4. Time differences from place to place: the earth rotates through 360o
in every 24 hours which means that
for every one hour, it passes through 15o
. since the earth moves from west to east, it means that for every
15o
, the east is always one hour ahead of time while the west is always on hour behind time.
5. Daily rising and falling of the tides: during rotation of the earth, it results in the rising and falling in the
level of water in the seas and oceans. Owing to the rotation of the earth, the tide-producing forces cause
the surface of the water to oscillate, resulting in the rising and falling in the level of water in the seas and
oceans.
6. Dawn and Twilight: Dawn refers to the brief period between sunrise and full daylight while twilight
refers to the brief period between sunset and completer darkness. Dawn and twilight which are the results
of rotation caused by the earth receive diffused reflected light from the sun while it is still below the
horizon.
EARTH’S MOVEMENT (REVOLUTION AND EFFECTS)
DEFINITION
The Revolution of the earth is defined as the movement of the earth around the sun in its orbit.
- The revolving earth is titled or inclined at an angle of 66
1
2
o
to the plane of the ecliptic during its
revolution.
- It takes the earth 365
1
4
days to complete one revolution (ie moves round the sun).
- The revolution of the earth causes four seasons in a year.
- The ¼ days or 6 hours are added up every four years to make an extra day in a leap year. A leap year has
366 days while a normal year has 365 days.
Differences between Rotation and Revolution
Rotation Revolution
i. The earth rotates on its axis It revolves around the sun along its orbit.
ii. The earth rotates through 36o
in 24 hours
(one day)
It revolves around the sun in 365
1
4
days (one year)
iii. The rotating earth is inclined at an angle of
23
1
2
The revolving earth is tilted or inclined at an angle of 66
1
2
o
to the plane of the ecliptic.
iv. Rotation causes day and night Revolution causes seasons.
v. Rotation causes the difference of one hour
between two meridians -15o
apart.
Revolution causes changes in the altitude of the mid-day
sun.

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Effects of Revolution of the Earth

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1. It determines a year: the time taken by the earth to move around the sun (i.e. complete its orbit) is fixed at
365
1
4
days which make up a year.
2. Varying the length of day and night at different times of the year: the length of day and night varies
depending on the position of the earth in relation to the sun. (Fig. 4.7)
In the Northern Hemisphere, during the winter around December 22, as we go northwards, the hours of
darkness increase. At the arctic circle (66
1
2
o
N), the sun never rises and there is darkness for the whole day
(December, 22). But in the southern hemisphere, the period of daylight increases towards the South pole on
December, 22, and the region experiences summer. In the Northern hemisphere, during summer around June
21, the periods or hours of daylight increase as we go towards the North Pole. At the Arctic Circle (66
1
2
o
), the
sun never sets by June 21, and there is a complete twenty-four-hour period of continuous daylight this region
(arctic circle) at this time is called The Land of the Midnight sun. The sun is overhead at the Tropic of
Cancer and no part is in darkness.
Summary of effects of revolution on the length of day and night in the Northern hemisphere.
i. The length of day and night varies depending on the position of the earth in relation to the
sun.
ii. The periods of daylight increase during summer as we move towards the north pole.
iii. At the Arctic Circle (66
1
2
o
N) there is a complete 24 hours period of continuous daylight on
June 21.
iv. The region from Arctic Circle to the North Pole at this time is called “the land of the Midnight
sun”.
v. This period is when the sun is overhead at the Tropic of Cancer.
vi. In the winter period around December 22, the hours of darkness increase towards the North
Pole.
vii. The “Sun never rises at the Arctic Circle.”
viii. There is complete darkness for the whole day on December 22.
ix. During this period, the sun is directly overhead at the Tropic of Capricorn,
x. There is equal day and night during the equinox.
xi. The sun is directly overhead at the equator on March 21 and September 23.
in the Southern Hemisphere, the period of darkness increases towards the South pole on June 21st
, but the
region experiences winter.
It causes seasons: In tropical areas like West Africa, including Nigeria, there are two seasons – the rainy
season and the dry season. But in temperate countries, the revolution of the earth causes four seasons –
winter, spring, autumn, and summer,
Changes in the altitude of the mid-day sun: As a result of the earth’s revolution, the altitude (height) of the
mid-day sun changes, resulting in Equinoxes and Solstices.
a. Equinoxes:
(i) This is the time when the mid-day sun is directly overhead at the equator.
(ii) The equinoxes occur on March 21 and September 23.
(iii) The Equinoxes mean there is equal day and equal night i.e. moon March 21 and September 23.
(iv) There is twelve hours of daylight and twelve hours of darkness.
(v) During equinoxes, all places on the earth have equal days and nights on these two days.
(vi) March 21 is also called Spring Equinox while September 23 is called Autumn Equinox.
b. Solstices
(i) This is the time when the sun is vertically overhead at the Tropic of Cancer or at the Tropic of
Capricorn.
(ii) The solstices occur on December 22 and June 21

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(iii) The solstices mean that the period of day and night is not equal.
On June 21, the sin is overhead at the Tropic of Cancer, resulting in June or Sumer’s solstice.
This means that the northern hemisphere will have its longest day and shortest night.
On December 22, the sun is overhead at the Tropic of Capricorn, resulting in the December winter solstice
which means that the Southern hemisphere will have its longest day and shortest night. The Tropic of Cancer
and the Tropic of Capricorn mark the limit of the overhead sun. Outside these two points, the sun is never
overhead at any time of the year.
Differences Between Equinox and Solstice
During equinox, all places have equal days and equal nights while during the solstice, the places have longer
days in summer and longer nights in winter.
i. Equinox occurs on March 21 and September 22 while solstice occurs on June 21 and December 22.
ii. During equinox, the sun is overhead at the Tropic of Cancer or the Tropic of Capricorn.
iii. Equinox could be spring or autumn while solstice could be summer or winter.
5. Changes in seasonal temperature: It is observed that summers are usually warm and bright, while
winters are cold and dark in the arctic region. The reasons include:
i. During summer, the zenith angle of the sun is higher.
ii. The concentration of heat over a small area leads to high temperatures.
iii. In winter, the oblique rays of the sun fall faintly over a large area.
iv. The little heat makes the temperature remain low.
v. There are twenty hours of daylight in summer solstice and twenty hours of darkness in winter.
vi. Days are longer than nights in summer while in winter, nights are longer.
(a) Reasons why all areas north of the Arctic Circle have 24 hours of daylight on June 21
On June 21,
- The sun is overhead at the Tropic of Cancer.
- In Arctic Circle, sun is seen every
- Where at the same time.
- The earth’s axis is inclined to the elliptical plane at an angle of 66
1
4
.
- No part is in darkness.
(b) Reasons why areas within the tropics have more sunshine than areas outside the tropics
There is more sunshine in the tropics because:
- Apparent movement of the sun is always from one tropic to the other and back.
- The sun is always overhead within the tropics.
- Within the tropics, the angle of incidence is vertical while it is slanting polewards.
- There is more insolation in the tropics than outside the tropics.
- Difference in length of day and night is hardly noticeable in the tropics.
ECLIPSE, DAWN, AND TWILIGHT
ECLIPSE
An eclipse is formed when the three bodies – the sun, the earth, and the moon are in a straight line during the
movement of the earth. The moon revolves around the earth once every twenty-eight days (a month), and the
earth and the moon travel together, making a complete movement around the sun once in a year. During this
movement, there will be a time when these three bodies (earth, sun, and moon) will be in straight line as shown
in Fig. 4.7 and Fig. 4.8. When this occurs, the light from the sun is obscured from reaching either the earth or
the moon. This phenomenon is known as an eclipse.

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Types of Eclipse
There are two types of eclipse. These are: (1) Eclipse of the moon (Lunar eclipse): this occurs within the
earth comes in-between the Moon and the sun. (Fig. 4.8). The earth, being larger than the moon can
completely obscure or cover the sun’s light from reaching the moon. This condition is known as eclipse of
the moon or lunar eclipse. This type of eclipse can lead to full darkness of the moon described as Total or
annular type of eclipse.
DIAGRAM
(2) Eclipse of the Sun (Solar eclipse): This occurs when the moon comes in-between the sun and the earth, Fig.
4.9 in a perfect straight line. The moon is capable of blocking the light from the sun. The moon then casts
its shadow of darkness on the earth. This condition is known as the eclipse of the sun or Solar eclipse. This
type of eclipse can lead to partial darkness of the earth called partial eclipse.
Eclipse is described as total eclipse if the body, e.g. moon is completely covered or shaded from the sun
by the earth. Eclipse is described as partial eclipse if the body, e.g. earth is half covered or shaded from the
sun by the moon. Eclipse is also described as annular eclipse if the body, e.g. earth is covered at centre
with darkness while the outer part is not, as shown in Fig. 4.10.
DIAGRAM
Date Eclipse Type Central Duration Geographic region of
visibility
Sept. 11, 2007 Partial S/America, Antarctica
Aug. 1, 2008 Total 2min. 27sec. N/America, Euro[a,
Asia
(Total) N/Canada,
Greenland, Siberia.
Jan. 26, 2009 Annular 7min. 45sec. Mongolia, China, S/E
Asia, Austra (Annular:
S/India, Sumatra.
Borneo).
July. 22, 2009 Total 6min. 39sec. E/Asia, Pacific Ocean,
Hawaii (Total: India,
Nepal, China C Pacific)
Jan. 15, 2010 Annular 11min. 08sec. Africa, Asia, (Annular:
C/Africa, India,
Malyman China).
July. 11, 2010 Total 5min. 20sec. S/America (Total:
S/Pacific, Easter Island,
Chile, Agentina.
Dawn and Twilight
Dawn refers to the brief period between sunrise and full daylight.
Twilight refers to the brief period between sunset and complete darkness.
- Dawn and twilight occur because the earth receives diffused or reflected light from the sun while it is still
below the horizon.
- In the case of twilight, there is little or no twilight at the equator because the sun rises or sets rapidly.
- The sun rises almost vertically from the horizon at the equator.
- Twilight occurs longer at higher latitudes because the sun sets more slowly.
- The sun rises and sets at a low level.
- Therefore, there are longer periods of twilight than full day light at the arctic circle.
Revision Questions

14
1.(a) Draw a diagram to show the four major positions of the earth during its revolution around the sun.
(b) Describe the effects of the revolution of the earth (SSCE Nov. 1989)
2(a) State three reasons to show that the earth is spherical.
(b) Describe three effects of revolution of the earth.
(c) Calculate the noon altitude of the sun at the Tropic of Capricorn on June 21st
. (SSCE Nov. 1990).
3(a) Distinguish between rotation and revolution of the earth.
(b). highlight any two effects of either rotation or revolution of the earth.
(c) With the aid of a suitable diagram, describe an eclipse of the sun. (SSCE August, 1991).
4(a) Write explanatory notes on the:
i. Equinoxes
ii. Great Circles
b. Explain why the period of twilight is longer along the Arctic Circle than at the Equator. (SSCE June
1992)
1. Highlight any three effects of either rotation or revolution of the earth.
(b) Give reasons why:
i. All areas north of the arctic circle have 24 hours of daylight on June 21st
ii. Areas within the tropics have more sunshine than areas outside the tropics. (SSCE June 1994).
2. With the aid of a diagram, describe the four positions of the earth during its revolution around the sun.
b. Explain why summers are usually warm and bright while winters are cold and dark in the Arctic region.
(SSCE Nov, 1997).
3. Using relevant sketches, distinguish between:
a. Solstice and equinox.
b. The earth’s rotation and revolution.
c. Parallels of latitude and meridians of longitude. (SSCE June, 1997).
4. Write explanatory notes on
i. Rotation of the earth.
ii. Revolution of the earth.
(b). State any three effects of the rotation of the earth. (SSCE Nov, 1997)
9. What is the shape of the earth?
a. With the aid of appropriate diagrams, give four proofs to support your answer in (a) above.
10. Write explanatory notes on each of the following:
a. The Sun
b. Twilight
c. Earth’s orbit
11. Define revolution of the earth.
b. Describe how revolution of the earth affects the length of day and night in the Northern Hemisphere

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