GEOGRAPHY FORM ONE TOPIC 2: MAJOR FEATURES OF THE EARTH'S SURFACE

 
MAJOR FEATURES OF THE EARTH'S SURFACE
Meaning of a Continent
Explain the meaning of a continent
The land surface occupies 29% of the surface of the globe, and the remaining 71% is covered by water. The land surface forms seven continents. A continent is a major landmass rising from the ocean floor. It includes islands adjacent to the continent. There are seven continents namely, Africa, Asia, South America, North America, Europe, Australia and Antarctica. These continents are surrounded by the following oceans: The Indian Ocean, the Atlantic Ocean, the Pacific Ocean, the Arctic Ocean and the Southern ocean.
There is more land surface in the northern hemisphere than in the southern hemisphere but there is more water surface in the southern hemisphere than in the northern hemisphere. The continents are broader in the northern hemisphere. The seven continents that make up the globe are explained below:
  1. Australia: Australia is the smallest continent and it is about a quarter of the size of Africa. Its size is about 8.5 million square kilometres. Australia is approximately 10°S and 40°S and between 115°E and 150°E. The islands of New Zealand to the south east of Australia are part of this continent. The continent is bordered to the west and north by the Indian Ocean, to the east by the Pacific Ocean, and to the south by the Southern Ocean.
  2. Europe: Europe is the sixth continent in size and it is about two-fifth the size of Africa. The size of Europe is 9.8 million square kilometres. Most of Europe lies between 40°N and the 1 Arctic circle, and between 10°W and 60°E. It lies to the west of Asia, separated by the Ural Mountains. Europe is bordered to the north by the Arctic Ocean, to the west by the Atlantic Ocean, and to the south by the Mediterranean Sea.
  3. Antarctica: Antarctica is the fifth continent in size and it is about one-third the size of Africa. Its area is about 11.4 million square kilometres. This is the southernmost continent, forming a circle at the South Pole and extends south of 661⁄2°S. It is surrounded by the southern ocean. The continent is mostly uninhabited.
  4. North America: North America is the fourth continent in size and it is slightly more than half the size of Africa. Its size is about 17.9 million square kilometres. If extends from 10°N to 65°N and from 60°W to 160°W. It is bordered to the west by the Pacific Ocean, to the East by the Atlantic Ocean, and the North by the Arctic Ocean.
  5. South America: South America is the third largest continent and it is about two-thirds the size of Africa. Its size is about 24.3 million square kilometres. It lies between 10°N and 50°S and between 35°W and 80°W. This continent is bordered to the east by the Atlantic Ocean, to the West by the Pacific Ocean, and it is joined to North America by the Isthmus of Panama.
  6. Africa: Africa is the second largest continent with an area of about 3.6 square kilometres. Africa extends from 37°N to 35°S and from 50°W to 50°E and it is crossed by Tropics of Cancer and Capricorn. Thus the greater part, about three quarters of the whole area lies in the tropics. Africa is bordered to the north by the Mediterranean Sea, to the west by the Atlantic Ocean, and to the East by the Indian Ocean.
  7. Asia: Asia is the largest of all continents. It covers more than one third of the land surface of the earth. It is approximately one and a half times the size of Africa. Its total area is about 45.6 million square kilometres. Asia stretches from 0° to 67°N and from 30°E to about 18°E. The Ural Mountains form the boundary between Asia and Europe. This continent is attached to Africa by the narrow Isthmus of Suez which has been dug to form the Suez Canal. The continent is bordered to the North by the Arctic Ocean, to the East by the Pacific Ocean, and to the South by the Indian Ocean.
The following table summarizes the location and area of all seven continents discussed above:
ContinentGeographical locationArea (Million Km2)
Asia0° - 67° N; 30° - 180° E45.6
Africa37° N - 55° S; 15° W - 50° E30.6
South America10° N - 50° S; 35° W - 80° W24.3
North America10° N - 65° N; 60° W - 160° W17.9
AntarcticaBetween the South Pole and 66½ °S11.4
Europe40° N and the Arctic Circle ; 10° W - 60° E9.8
Australia10° S - 40° S; 115° E - 150° E8.5
Major Features of the Continent
Identify the major features of the continent
The surface of the continents is not smooth. It has mountains, hills, rivers and valleys, plateaus, and plains. Mountains are landforms which have high relief generally over 300 metres above the surrounding area. Hills are landforms that have moderate relief generally between 150 and 300 metres above the surrounding area. Plateaus are extensivehighland areas with more or less uniform summit level, bounded by one or more slopes falling steeply away, sometimes rising on one or more sides by steep slopes to mountain ridges. Plains are continuous sketches of comparatively flat land not much above sea level, sometimes gently rolling or undulating.
Mountains
There are four types of mountains. These are the Fold Mountains, Block Mountains, Residual Mountains, and Volcanic Mountains. These mountains are all named according to the way they were formed.
  • Fold Mountains:Fold Mountains are formed by wrinkling or (folding) of the Earth’s crust. Fold Mountains usually form parallel ranges which extend for hundreds of miles across a continent. Thus, Fold Mountains are the most extensive ranges in the world. For example, the Rocky Mountains in North America vary in width from 640 to 1,600 kilometres and are about 5,000 kilometres in length. These types of mountains have some of the highest peaks in the world. Mount Everest in the Himalayas is 8,848 metres above sea level and the Aconcagua in the Andes is 7,003 metres above sea level. Examples of Fold Mountains include the Himalayas in Asia; the Rockies in North America; the Andes in South America; the Alps in Europe; the Atlas in North Africa; the Cape ranges in South Africa; the Appalachians in the USA; and the Great Dividing Ranges in Australia.
  • Block Mountains:Block Mountains are formed when a movement in the earth’s crust forces the rocks to break instead of folding. As a result enormous cracks or faults are formed. When two sets of faults run parallel to each other and the ground between is forced to rise up, a block (fault) mountain is formed. Usually Block Mountains do not extend over wide areas as Fold Mountains do. Examples of Block Mountains are the Usambara, Uluguru and Ruwenzori Mountains in Africa; the Vosges and Black Forest Mountains in Europe; and Mount Sinai in Asia.
  • Residual Mountains:Residual mountains are formed when an area of highland remains standing above the general level of land after the rivers and other natural agents have lowered the surface of the surrounding area. Sometimes such highlands are called mountains of denudation. These mountains may in some cases appear as isolated hills but in other cases they appear as long ridges, generally steep on one side (the scarp slope) and gentle on the other side (dip slope). Examples of residual mountains are the Ahaggar Mountains of central Sahara; the Sekenke hills of Singida in Tanzania; the Admawa mountains of eastern Nigeria; the Highlands of Scotland; the Sierras of central Spain; and the Mesas and Buttes of the western plateau of the United States.
  • Volcanic Mountains:Volcanic mountains are formed from the piling up and cooling of hot molten lava and ashes that are thrown out from the earth’s interior after a volcanic eruption. Some of the volcanic mountains existing today were built up by a single eruption, but others were built by several eruptions. Volcanic eruptions are still taking place in some parts of the earth. Among the existing volcanic mountains, some still experience periodic eruptions, for example, the Vesuvius in Italy; the Krakatoa in Indonesia; the Mufimbiro in Uganda; and the Oldoinyo-Lengai in Tanzania. The Volcanic Mountains that still experience periodic eruptions are called active volcanic mountains.The Volcanic Mountains which erupted once in historical times and are no longer active are said to be dormant. In this group are included the Kilimanjaro and Meru mountains in Tanzania. Those volcanic mountains which have never experienced eruption and have shown no signs of erupting again are said to be extinct (dead). Included in this group are mountains Kenya, Elgon, Ngorongoro and Rungwe in East Africa; and Demavend in Iran.Volcanic mountains are usually conical in shape and mostly contain craters or depressions at their summits, for example, mountains Fujiyama and Kilimanjaro. Sometimes the craters are filled with water to form crater lakes.
Plateaus
In geology and earth science, a plateau (plural: plateaus or plateaux), also called a high plain or tableland, is an area of highland, usually consisting of relatively flat terrain that is raised significantly above the surrounding area, often with one or more sides with steep slopes.
The largest and highest plateau in the world is the Tibetan Plateau, called the "roof of the world”. The Tibetan plateau covers approximately 2,500,000 km2 at about 5,000 m above sea level.
The second-highest plateau is Deosai National Park (also known as Deoasai Plains) at an average elevation of 4,114 m and is located in the Skardu District of Gilgit-Baltistan, in northern Pakistan.
The third-largest plateau is the Antarctic Plateau, which covers most of central Antarctica, where there are no known mountains, but rather 3,000 m or more of ice.
Other plateaus in the world include the Colorado Plateau (North America); the Great Central Plateau, Ahagger Plateau and Fouta Djallon Plateau (Africa); Brazilian Plateau (South America), Mexican Plateau and Laurentian Plateau (North America); Arabian Plateau, Deccan Plateau and Tibet Plateau (Asia).
Plains
A plain is a broad area of relatively flat land. Plains are one of the major landforms, or types of land, on Earth. They cover more than one-third of the world’s land area. Plains exist on every continent except Antarctica. Plains occur as lowlands and at the bottoms of valleys but also on plateaus or uplands at high elevations.
Plains in many areas are important for agriculture because where the soils were deposited as sediments they may be deep and fertile, and the flatness facilitates mechanization of crop production; or because they support grasslands which provide good pasture for livestock.
Plains vary widely in size. The smallest occupy only a few hectares, whereas the largest cover hundreds of thousands of square kilometres. For example, the Great Plains of North America extends from Pyrenees Range on the French–Spanish border across northern Europe and Asia, almost halfway around the world.

The Yellow River winds through the plains of Sichuan, China. Many rivers are surrounded by plains, or broad areas of flat land.

Meaning of a Water Body
Define a water body
A water body is any significant accumulation of water, generally on a planet's surface. The term most often refers to oceans, seas, and lakes, but it includes smaller pools of water such as ponds, wetlands, or more rarely, puddles. A body of water does not have to be still or contained. Rivers, streams, canals, and other geographical features where water moves from one place to another are also considered water bodies.
Oceans and Other Water Bodies
Identify the oceans and other water bodies
An ocean is defined as a body of saline water covering much of the earth. The largest ocean is the Pacific. Its area is about 165.3 million square kilometres. The second largest ocean is the Atlantic, which covers about 82.2 million square kilometres. The IndianOcean, covering about 73.4 square kilometres is the third largest, followed by the Arctic Ocean, covering about 14.0 million square kilometres.
Composition of ocean water
Ocean water contains a number of dissolved mineral salts. These mineral salts include sodium chloride (common salt) which makes up 78% of all salt in the ocean water; and compounds of magnesium, potassium and calcium. Most of the minerals in the ocean are a result of constant accumulation since the formation of the oceans. However, a small amount of the minerals come from the land, having been dissolved by water and brought into the ocean by rivers. But the mineral salts in rivers are only in very small quantities.
The saltiness of the ocean water is not the same everywhere. Saltiness of the ocean water depends mainly on temperature which affects the amount of salt that can dissolve in the water, the amount of fresh water brought into the ocean by rivers and rainfall, and the amount of evaporation taking place from the surface.
Water temperature
Water is heated by the sun’s rays much more slowly than land is. Water also loses heat to the air around it more slowly than the land does. This causes the temperature of the sea water to vary only slightly from season to season. In general, the temperature of the ocean water decreases from the equator, where the surface temperature is 25°C to the polar regions where the water is very cold (-2.2°C). But the decrease in temperature poleward is not uniform because of the occurrence of warm and cold ocean currents. Onthe other hand, water temperature decreases with depth in the tropics up to the depth where the temperature is 1.1°C.
Water movements
Ocean water is constantly in motion. There are two types of movement. One is horizontal movement, which is in the form of ocean currents and tides, and the other is vertical, which is the rising of subsurface water and the sinking of the surface water. The movements of ocean water are a result of density variations in the water which is particularly important in vertical movements and winds which are particularly important in horizontal movements.
An ocean current is the permanent or seasonal movement of surface water in the ocean. There are warm and cold currents, the ocean currents are set in motion by a combination of prevailing winds, differences in density and temperature of the ocean waters, the rotation of the earth, and the shape of landmass.
Tides are the rising and the falling in the level of water in the oceans, seas and lakes. They occur twice a day (in 24 hours). The level to which tides rise and fall varies from day to day. On the days when it rises to its highest level, it also falls to its lowest level. The rising and falling is caused by the pull of gravity of the moon and the sun.
Waves are to and from movements of the surface water. When water is thrown into waves, its surface gets a shape of ups and downs. The highest part of the wave is called the crest and the lowest the trough. The distance from one crest to the next, or from trough to trough is called the wavelength. Waves travel in some definite direction, andgive the impression that they move forward, but in reality only the shape moves forward while the water moves up and down. For example, a cork thrown into the water does not travel with the waves, it moves up and down and to and fro, but not forwards. A wave is driven on the shore by wind, and its height and force are determined by the strength of the wind and the distance of open water over which it has blown.

Water waves
Lakes
A lake is a natural or man-made body of water that is surrounded by land. Lakes lie on land and are not part of the ocean, and therefore are distinct from lagoons, and are also larger and deeper than ponds, though there are no official or scientific definitions. Most lakes are fed and drained by rivers and streams.
Some lakes are artificial (man-made lakes) and are constructed for industrial or agricultural use, for hydro-electric power generation or domestic water supply, or for aesthetic or recreational purposes. Examples of man-made lakes include Lake Nasser (in Egypt), Lake Kariba (Zambia), and Lake Volta (Ghana).
The majority of lakes on Earth are fresh water, and most lie in the Northern Hemisphere at higher latitudes. Most lakes have at least one natural outflow in the form of a river or stream, which maintains a lake's average level by allowing the drainage of excess water. However, some lakes do not have a natural outflow and lose water solely by evaporation or underground seepage or both.
Lakes are not evenly distributed on the earth's surface; most are located in high latitudes and mountainous regions. Although lakes are usually thought to be freshwater bodies, many lakes, especially in arid regions, become quite salty because a high rate of evaporation concentrates inflowing salts. The Caspian Sea, Dead Sea, and Great Salt Lake are among the greatest of the world's salty lakes. The Great Lakes of the United States and Canada is the world's largest system of freshwater lakes. Lake Superior alone is the world's largest freshwater lake with an area of 82,414 sq km. The Caspian Sea is the largest lake in the world, with an area of 372,960 sq km. Lake Titicaca in the AndesMountains of South America is the world’s highest lake at 3,800 m above sea level; while the Dead Sea is the lowest at 425 m below sea level.
Rivers
A river is natural water flowing in a definite channel towards an ocean, sea, lake, desert basin, marsh or another river. In some cases, a river flows into the ground and become dry at the end of its course without reaching another body of water. Small rivers can be referred to using names such as stream, creek, brook, rivulet, and rill.
Rivers are part of the hydrological cycle. Water generally collects in a river from precipitation through a drainage basin from surface runoff and other sources such as groundwater, springs, and the release of stored water in natural ice and snowpacks (e.g. from glaciers).
Examples of rivers in Africa include the Nile, Congo, Niger, Zambezi and Orange. In Tanzania we have rivers like Rufiji, Ruvuma, Ruaha, Pangani, Wami and Malagalasi.
Features of the Ocean Floor
Describe the features of the ocean floor
The floor of the ocean is irregular. The major relief features of the ocean floor are explained below:
  1. Continental shelf:This is a gentle-slope margin of a continent that forms the shallow areas of oceans. These shallow areas extend from the coast to a depth of about 200 metres towards the ocean, and usually end suddenly.
  2. Continental slope:The continental slope is found at the point where the continental shelf forms a steep slope with the lower slope of the ocean floor towards the sea.
  3. Ridge:A ridge is the raised part of the ocean floor. Some of these rides appear above the surface of the oceans as oceanic islands.
  4. Ocean deep or trench:An ocean deep is a long, narrow depression (or trough) found on the ocean floor.
  5. Deep sea plain (ocean plain):An ocean plain is the most extensive, flat area of the ocean floor. It is a monotonous and undulating area. A large part of the plain is covered by mud.

A generalized section across an ocean floor
The Map Showing the Distribution of Continents and Water Bodies
Draw the map to show the distribution of continents and water bodies
The Map showing distribution of water bodies.


GEOGRAPHY FORM ONE TOPIC 1: CONCEPT OF GEOGRAPHY


CONCEPT OF GEOGRAPHY
The Meaning of the Term Geography
Define the term geography
The term Geography is a combination of two Greek words: Geo and Graphein. Geo means Earth and Graphein means to write, draw or describe. These two words together form Geographia, which means to draw, write about or describe the Earth. These meanings led to the development of the early definition of geography which referred to description of the Earth by words, maps and statistics and included both the physical earth and everything found on it such as plants, animals and people. Therefore, Geography is the study of the distribution and interrelationship of phenomena in relation to the Earth surface. Alternatively,Geography can be described as the study of the Earth and its environment.
BRANCHES OF GEOGRAPHY
There are two branches of Geography, namely:
  1. Physical Geography - mainly concerned with land formation processes, weather and climate.
  2. Human and Economic Geography - involves the study of human activities on the Earth's surface
Explain the inter-relationship between different geographical phenomena
Physical and human environments make up the two major geographical phenomena. The word phenomena refers to facts or circumstances observed, or observable within nature. Therefore, a geographical phenomenon is an occurrence or fact in the geographical science. There exists an interrelationship between Geography and other subjects; physical and human environments lead to geographical phenomenon within the two types of environment. There are a variety of other geographical phenomena that are interrelated, for example land resources provide soil that support plants growth. Sun rays generate heat which lead to the evaporation of water; water vapour forms clouds and eventually rain is formed. Climate determines the types of plant and animal species that can survive in a particular geographical area and influences human population distribution. On the other hand, human activities can lead to modification of physical environments, for example soil degradation, land reclamation and forest conservation.
Components of the Solar System
Name the Components of the Solar System
Below are the components that make up the solar system:
  1. The Sun
  2. Planets
  3. Comets
  4. Asteroids
  5. Meteors; and
  6. Satellites
Importance of the Components of Solar System
Describe the importance of the components of solar system
Components of the Solar System are important because:
  1. They produce heat and light potential for living organisms, for example the Sun
  2. The provide habitat for humans and other living organisms, for example the Earth
  3. They form craters which later become attractive sites for tourism activities, for example meteors which produce meteorites that fall on the Earth's surface and form craters


The Sun is a star.
Dimension of the Sun in Relation to Other Space Bodies
State the dimension of the sun in relation to other space bodies
Dimension of the Sun relative to other Space Bodies: The diameter of the sun is 1.4 million kilometers
Characteristics of the Sun
Describe the characteristics of the sun
The Sun is composed of approximately 75% Hydrogen, 23% Helium and 3% other elements. Therefore, the elements which make up the Earth comprise only a small fraction of the materials which form the Sun. These include Carbon, Iron, Oxygen, Silicon etc. The Sun is the only source of light and heat that the planet receives. The temperature of the Sun is estimated to be 20,000,000 degrees Centigrade.

The Term Solar Energy
Define the term solar energy
Solar energy is the heat and light produced from the Sun. The Sun is the source of all energy on the Earth.
Different Uses of Solar Energy
Suggest different uses of solar energy
Some of the different uses of Solar energy include:
  1. Drying clothes, meat, fish, fruits and grains
  2. Photosynthesis ingrowing plants to manufacture their own food
  3. Generation of electricity
  4. Formation of coal, gas and oil
  5. Formation of clouds and rainfall through evaporation of water caused by the heat of the Sun
  6. Giving power to small radios and running small telephone systems by using silicon solar batteries
  7. Source of Vitamin D to human bodies as the bodies absorb Sunlight
  8. For domestic purposes like cooking food, heating, water.
How the Use of Solar Energy Promotes Environmental Conservation
Explain how the use of solar energy promotes environmental conservation
Utilization of Solar energy in manufacturing industries reduces the production of chlorine from industrially produced chlorofluorocarbon gases which cause depletion of the ozone layer. The depletion of the ozone layer causes global warming. Solar energy is used as an alternative source of energy, therefore reducing the depletion of forests for charcoal and firewood.
How Solar Energy May Contribute to Emancipation of Women
Explain how solar energy may contribute to emancipation of women
REDUCED TIME BURDENS LEADING TO HIGHER-EARNING JOBS AND INCREASED ENTREPRENEURIAL OPPORTUNITIES
Women are often disproportionately responsible for household duties. This is particularly acute in rural settings, where women spend considerable time on tasks such as collecting firewood for basic cooking, heating, and lighting needs. Access to energy allows for more efficient products—from those as basic as a solar lantern to those as advanced as a washing machine. These products can reduce the time burdens of domestic responsibilities and create time for more productive, formal engagement in the local economy outside the home. Empirical studies that have examined the impact of electrification on female labor rates in developing country settings reinforce this hypothesis.
IMPROVED BASELINE CONDITIONS LEADING TO GREATER ACCESS TO ECONOMIC OPPORTUNITIES
There are a multitude of studies that demonstrate that improved access to electricity improves baseline living conditions for women. These studies show improvements to women’s health through cleaner indoor air; better nutrition and food safety due to improved refrigeration; and improved health knowledge through better access to mass media and more time to read.Interior and exterior lighting in rural settings often means improved security for women, enabling greater mobility to engage in productive activities under safe conditions. Anecdotal evidence also shows improved education for girls as a result of access to electricity, although most empirical studies do not show gender-differentiated impacts.Improving these baseline conditions facilitates the ease by which women can participate in the local economy: Healthy, safe, and informed individuals are more apt to be productive.


Planets in the Solar System
Locate the planets in the solar system
Planets are bodies that revolve around the Sun. Previously, they included Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Pluto does not qualify to be a planet anymore as it is the smallest and does not revolve around the Sun. Therefore, there are currently officially only eight planets in our Solar System. The word 'Planet' originates from the Greek word 'Planetai' which means 'Wandering' as the planets seem to move about in the Sky as wandering stars. All planets revolve around the Sun in the same direction in orbits that are elliptical and nearly in the same plane. The time taken to complete an orbit depends on the distance from the Sun.
Relative Distance of Planets from the Earth
Show relative distance of planets from the earth
How far is each planet from Earth?
sually when people ask this question, what they mean is "What is the distance between the orbit of Earth and the orbit of each planet?" or "What is the closest that each planet comes to Earth?" (These are essentially the same question, because the planets can't get any closer than their orbital spacing allows.) You can compute this in a rough way by assuming that the orbits are circular and coplanar, and looking at the planet-to-Sun distance for each planet. Since the distances are so large, we usually express them in Astronomical Units (AU). (AnAUis the average distance from Earth to the Sun, about 150 million kilometers or 93 million miles.) The table below lists the distance of each planet from the Sun in AU.
PlanetAverage distance from Sun in AU
Mercury0.39
Venus0.72
Earth1.00
Mars1.52
Jupiter5.20
Saturn9.58
Uranus19.20
Neptune30.05
Pluto (dwarf planet)39.48

Characteristics of Comets, Asteroids, Meteors and Satellites
Describe the characteristics of comets, asteroids, meteors and satellites
Comets are objects with leading heads and bright tails in the Sky. Sometimes they can be seen at night. They are composed of ice crystals and fragments of solid matter. They have highly elongated orbits around the Sun. They can be seen from the Earth only when they come close to the Sun.
Asteroids are solid heavenly bodies revolving around the Sun. They are mostly found between the orbits of Mars and Jupiter. They are in thousands and the largest has adiameter of just less than 800 Kilometres. The bodies can only be seen with a telescope because they are very far away.
Meteors are pieces of hard matter falling from outer Space. They can be seen when they come close to the earth, at about 110-145 Kilometres, whereas as a result of friction with the atmosphere, they become hot and usually disintegrated. They fall on the Earth's surface as large boulders known as meteorites, or a meteor if it is one. These bodies are made of Nickel, Iron and Silica.
Satellites are the moons of the Planets and they can be defined as the small bodies which rotate on their axis and revolve around the Sun. There are only seven (7) planets which have satellites apart from 57 satellites in the Solar System. The number of satellites depends on the size and nature of the planet.
Local Incidents Linked to Meteorites
Narrate local incidents linked to meteorites
There are two known meteorites in Tanzania. One is found in Mbozi district in Mbeya region and the other is inMalampaka in the Kwimba district in Mwanza region. These falling meteorites have resulted in the formation of craters.

The Earth is the only Planet among the planets in the Solar System that is known to support life. (Pluto does not qualify as a planet any moreasit is the smallest and does not revolve around the sun). The Earth is made up of the atmosphere (air), hydrosphere (water bodies), the solid crust, molten materials and the biosphere (living organism). Water bodies cover about three quarters of the Earth's surface.
The Shape of the Earth and its Evidence
Describe the shape of the earth and its evidence
There are many ways to prove that the earth is spherical. The following are some of them:
  1. CIRCUMNAVIGATION OF THE EARTH: The first voyage around the world by Ferdinand Magellan and his crew, from 1519 to 1522, proved beyond doubt that the earth is spherical. No traveller going round the world by land or sea has ever encountered an abrupt edge, over which he would fall. Modern air routes and ocean navigation are based on the assumption that the earth is round.
  2. THE CIRCULAR HORIZON: The distant horizon viewed from the deck of a ship at sea, or from a cliff on land is always and everywhere circular in shape. This circular horizon widens with increasing altitude and could only be seen on a spherical body.
  3. SHIP'S VISIBILITY: When a ship appears over the distant horizon, the top of the mast is seen first before the hull. In the same way, when it leaves habour, its disappearance over the curved surface is equally gradual. If the earth were flat, the entire ship would be seen or obscured all at once.
  4. SUNRISE AND SUNSET: The sun rises and sets at different times in different places. As the earth rotates from west to east, places in the east see the sun earlier than those in the west. If the earth were flat, the whole world would have sunrise and sunset at the same time. But we know this is not so.
  5. THE LUNAR ECLIPSE: The shadow cast by the earth on the moon during a lunar eclipse is always circular. It takes the outline of an arc of a circle. Only a sphere can cast such a circular shadow.
  6. PLANETARY BODIES ARE SPHERICAL: All observations from telescopes reveal that the planetary bodies, the sun, moon, satellites and stars have circular outlines from whichever angle you see them. They are strictly spheres. Earth, by analogy, cannot be the only exception.
  7. DRIVING POLES ON LEVEL GROUND ON A CURVED EARTH: Engineers when driving poles of equal length at regular intervals on the ground have found they do not give a perfect horizontal level. The centre pole normally projects slightly above the poles at either end because of the curvature of the earth. Surveyors and field engineers therefore have to make certain corrections for this inevitable curvature, i.e. 12.6 cm to 1 km.
  8. SPACE PHOTOGRAPHS: Pictures taken from high altitudes by rockets and satellites show clearly the curved edge of the earth. This is perhaps the most convincing and the most up-to-date proof of the earth's sphericity.


Types of Earth's Movements
Describe the types of earth's movements
The Earth is in motion all the time. People cannot feel this motion because they move with it like all other planets. There are two types of movements of the earth, namely:
  1. The rotation of the Earth on its own axis
  2. The revolution of the Earth around the Sun
The Term Rotation
Describe the term rotation
Rotation refers to thespinning of a body on its axis. The earth rotates or spins on its axis in an anti-clockwise direction, from West to East through 3600 in 24 hours. Thus for every 15 degrees of rotation, the earth takes one hour which is the same as four minutes for every 1 degree.
An axis is an imaginary line joining the N (North) and S (South) poles through the center of the Earth.
Note: The rotation of the earth is very rapid although it is difficult to feel itsmotion. At the equator, every point of the earth's surface is traveling Eastwards at about 1600 Km per hour. At latitude 40 degrees, the speed is about 1280 Km per hr.
Evidence to Prove that the Earth Rotates
Give evidence to prove that the earth rotates
Below is evidence that proves that the Earth rotates:
  1. During the night, stars appear to move across the sky from West to East
  2. If one travels in a fast moving vehicle, will notice trees and other objects on both sides of the road are moving fast in the opposite direction
  3. Rising of the sun over the eastern horizon in the morning. This shows that the point of observation, that is south, is moving by rotation from West to East
  4. Day and Night. During the Earth's rotations some regions face the sun while others do not face it. Thise regions facing the sun experience day time whereas the regions which are not facing the sun are in darkness (night). This proves that the earth is rotating.
Significances of Earth's Rotation
Explain the significances of earth's rotation
Alternation of day and night: Rotation of the earth causes the sides of the earth which face the sun to experience daylight which is the day, whereas the side that is not facing the sun at that time will be in darkness (night).
  1. The occurrence of tides in the ocean caused by gravitational forces of the moon and sun upon the rotation of the Earth
  2. Deflection of winds and ocean current
  3. Time difference between longitudes: The rotation is responsible for difference in time between different places on Earth. It causes the difference of one hour in every 15 degree interval between longitudes. The Earth rotates from West to East and takes 24 hours to complete one rotation. The difference in time is 4 minutes for each degree of longitude
The Term Revolution
Define the term revolution
Revolution is defined as the movement of one body around another. The earth revolves around the sun in an elliptical orbit. Due to the elliptical shape of the earth orbit the sun is closer to the earth at one point of the year than at another.
The farthest (maximum distance) position from the sun in orbit of the earth is called aphelion while the nearest position of the earth to the Sun is known as perihelion.
The Process of Revolution
Explain the process of revolution
The Earth is at aphelion each year on 4th July, when it is at the maximum distance of 152 million kilometer form the sun. The earth is at perihelion each year on 3rd January when it is at the minimum distance of 147 million kilometers.
The earth's revolution around the sun takes a year (365¼ days) therefore the speed of revolution is about 29.6 kilometers per second. A normal year has only 365 days. The remaining fraction of ¼ day is added once in four years to make a leap year of 366 days.
The Result of the Earth's Revolution Around the Sun
Describe the result of the earth's revolution around the sun
The result of the Earth's Revolution around the Sun:
  1. The four seasons of the year; summer, autumn, winter and spring. A season is one of the distinct period into which the year may be divided. In the northern hemisphere the summer season months are May, June and July. Autumn months are August, September and October, winter months are November, December and January and spring months are February, March and April. In the southern hemisphere summer season months are November, December and January. Autumn months are February, March and April. Winter months are May, June and July and spring months are August, September and October. Equinox refers to the period when the sun is overhead at the equator.
  2. Change in the position of the midday sun at different times of the year. As the earth revolves around the sun its position changes and makes it appear as if it is the sun moving.
  3. Varying lengths of the day and night at different times of the year. The axis of the earth is inclined to its elliptical plane at a certain angle of 66.5 degrees. If the axis of the earth were vertical, the sun rays would be overhead at the Equator, thus all places on the earth would always experience 12 hours of daylight and 12 hours of night


The Parallels and Meridians
Define the parallels and meridians
Latitude refers to the angular distance North or South of the equator measured in degrees, minutes and seconds. The equator is given a value of 00. It is an imaginary line which divides the Earth into two hemispheres. The Northern hemisphere has a latitude of 90o N and the Southern hemisphere has a latitude of 90o S.
Therefore, Parallels of latitude are particular lines joining all points on the surface of the earth and making an angle of 300o N with the equatorial plane.
How Latitudes and Longitudes are Determined
Describe how latitudes and longitudes are determined
THE IMPORTANT PARALLELS
The important parallels include:
  1. Equator 0o
  2. Tropic of Cancer 23.5oN
  3. Tropic of Capricorn 23.5oS
  4. Arctic Circles 66.5oN
  5. The Atlantic Circle 66.5oS
LONGITUDE
Refers to the angular distance measured in degrees East and West of the Greenwich Meridian.
Prime Meridian is the line running through the poles and the Greenwich observatory near London. It is also known as Greenwich Meridian.
All lines of longitude are semi circles of equal length. Lines of longitude are also called meridians. There are 360o in a circle, 180o lie east of the Greenwich Meridian and the other 180o west of Greenwich.
The Greenwich lines have been chosen by convention (meaning that any other lines could have served the same purpose).
CALCULATION OF TIME
The earth rotates on its own axis from West to East once every twenty four hours. This means 360oof longitude are covered in a period of 24 hours or 1o in four minutes. There are places on a given meridian that experience midday at the same time. Time recorded along the same meridian is known as Local Mean Time (LMT).
Example 1
When the local time of Accra is 2.00pm what will be the local time of Bangui 15 degrees E.
Solution
15 degrees - 0 degrees = 15 degrees
15 x 4 minutes = 60
60/60 = 1 hour
Accra 2.00 pm + 1.OO hour time difference = 3.00 pm
Importance of a Great Circle
Explain the importance of a great circle
Any circle which divides the globe into hemispheres is a great circle. The equator is a great circle and Greenwich Meridian together with Meridian 1800 make another great circle. The number of great circles is limit less.
The importance of great circles in geological applications of spherical projections is that they can represent planes. The center of a great circle is called its pole. If you know a great circle, you can find its pole, and if you know the pole, you can find the great circle. Thus it is possible to represent a plane by a single point. This fact is extensively used in advanced projection techniques. The perimeter of equatorial plane is called primitive circle.
CHARACTERISTICS OF GREAT CIRCLES
  1. All great circles divide the earth (sphere) into two hemispheres.
  2. A great circle is the largest possible circle that can be drawn on the surface of the sphere.
  3. The radius of great circles is the same as the radius of the earth.
USES OF GREAT CIRCLES
Great circles are used to plot routes for ships crossing the vast oceans and aircraft flying great distance in space. Ships and aircraft travel by following great circles in order to save fuel and time because the shortest route between two places is along the circle of the great circle which passes through them.
Importance of Parallels and Meridians
Discuss the importance of parallels and meridians
Parallels are another name for lines of latitude. You will see that these lines do not converge, or come together, anywhere on the globe. We call these parallels because they are always an equal distance apart. The first parallel is the equator. It is latitude 0. Latitude measures distance north and south from the Equator. Parallels are lines that circle the globe.
Meridians are another name for lines of longitude. These lines are drawn on maps and globes so that people can locate places. Meridians are lines that run from the North Pole to the South Pole. Meridians are not parallel. They converge or come together at the Poles. They number from the Prime Meridian (line 0) to 180W and from the Prime Meridian to 180E.
Local time
Calculate local time
Example 2
What is the local time at Morogoro-Tanzania when it is noon at Kigali-Rwanda?
Procedure
  1. Note the longitudinal position between the two points Kigali 30°E and Morogoro 45°E
  2. Find the difference in degrees of longitude between Kigali and Morogoro 45 degrees - 30 degrees = 15 degrees
  3. Multiply the difference by 4 minutes 15°x 4 minutes = 60 minutes; 60 ÷ 60 = 1 hour
  4. The time difference is to be added (+) in case of places to the East of a point. In case of place to the West, the time difference is subtracted (-). Since Morogoro is to the East of Kigali, Morogoro time will be ahead of that of Kigali's by 1 hour, therefore time for Morogoro will be:12.00 noon + 1 hour = 1.00 pm.
Time and Time Zone
Define time and time zone
Time means duration or suitable moment for some purpose.
Time zone refers to a zone where standard time is accepted throughout a longitudinal zone 150 in width.
Essence of Time and Time Zone
Explain the essence of time and time zone
The importance of time zones is to avoid the problems in telling time if every place had its own time set according to the local mean time.
The timetable of various human activities such as television and radio programs would be confusing if they had to show different times.
As the time varies from place to place, different stretches of land agreed to adopt the time from certain meridian, that time is known as standard time.
East African countries agreed to adopt standard time taken from meridian of 45oE.When a whole stretch of land keeps to the same standard time that stretch of land forms a time zone.
Variation of Standard Time in a Single Country
Explain variation of standard time in a single country
Large countries like USA, China, etc have several standard time zones with each time zone covering about 15 degrees of longitude. There are 24 times zones in the world. The starting point for dividing the world into 24 times zones is the Greenwich Meridian. The standard time for Greenwich is known as the Greenwich Meridian time (GMT).
International Date Line
Define International Date Line
The International Date Line is the line where date is changed or calendar day begins. This line follows approximately the 1800 meridian.
Location of International Date Line
Locate International Date Line
When the time is 6.00pm on Monday 25th December, at Greenwich, the time at 1800 E longitude will be 12 hours ahead of Greenwich Mean Time. The time at 1800 E will be 6.00am on Tuesday 26th December. Therefore if one travels eastwards and crosses the date line, one will gain a day whereas one who travels westwards across the line will loose a day.

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