Geography
THE SOLAR SYSTEM
Geography is the study of places and the relationship between people and their environment. Geographers explore both the physical properties of the Earth's surface and the human societies spread across it.In the context of dynamic and changing world, it is very crucial to study Geography so as to be able to achieve sustainable human development.
THE SOLAR SYSTEM
Introduction
In this topic, you will learn about the concept of the solar system, the Sun, solar energy and the planets. Also, you will learn about other bodies in the solar system, shape of the Earth, Earth’s movement and the importance of the parallels and meridians. The chapter ends with summary of the topic, revision questions and a list of references
The concept of solar system
Objectives
By the end of this topic you should be able to define the solar system, name the components of solar system and describe the importance of the components of solar system. Also, should be able to state the dimensions of the Sun relative to other space bodies and describe the characteristics of the Sun. In addition, should be able to define the ‘solar energy’, mention different uses of solar energy and explain how the use of solar energy promotes environmental conservation and how solar energy may contribute to emancipation of women. Moreover, should be able to locate the planets in the solar system, show the relative distances of planets from the Sun, describe the characteristics of comets, asteroids, meteors and satellites as well as narrate local incidents linked to meteorites, describe the shape of the earth and its evidence, describe the types of Earth’s movements. You should also describe the term ‘rotation’ describing the evidence to prove that the earth rotates, explain the significance of Earth’s rotation. You should be able to define the term 'revolution', explain the process of revolution, and describe the results of the Earth’s revolution around the Sun. Finally, you should be able to define the parallels and meridians, describe how latitudes and longitudes are determined, explain the importance of a great circle, discuss the importance of parallels and meridians, calculate local time, define time and time zone, explain the essence of time and time zones, explain variation of standard time in a single country, define International Date Line, and locate International Date Line
Define the Solar System
Meaning of Solar System
When we look at the sky at night we see thousands of bright bodies. These are stars and planets. Our Earth is one of the planets. Sometimes we can see a group of stars which form patterns called constellations. In some occasions, we can see bright, moving objects. These are called meteorites
The solar system refers to the Sun together with the eight planets and all other celestial (heavenly) bodies that orbit the Sun. The name ‘solar system’ is derived from a Latin word ‘sol’ which means Sun
Components of the solar system.
Components of the Solar System
The solar system is made up of the Sun, planets, moons, natural satellites, asteroids, meteors, comets, dust, ice and interplanetary space (it contains interplanetary dust and interplanetary gas)
All planets and other bodies revolve around the Sun. The Sun is the central body of the solar system, and it is the only body that generates its own heat. Bodies that revolve around the Sun are kept in their orbits (paths) by the Sun’s powerful force of gravity
There are eight known planets in the solar system. The planets, starting from the one closest to the Sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune
The four innermost planets in the solar system known as terrestrial planets include Mercury, Venus, Earth and Mars. They are called terrestrial because they have a compact, rocky surface like the Earth’s
Jupiter, Saturn, Uranus, and Neptune are known as the Jovian (Jupiter-like) planets because they are all huge compared with Earth, and they have a gaseous nature like Jupiter's. The Jovian planets are also referred to as the gas giants, although some or all of them might have small solid cores
You grew up learning that the solar system consists of nine planets, including Pluto as one as those planets. However, the International Astronomical Union (IAU) stripped Pluto of this status in 2006
When Pluto was discovered in 1930, it was hailed as the ninth planet in the solar system based on an overestimation of its size. But it looked not fitting among the larger planets following the discovery of swarms of ‘ice dwarfs’—icy rocks in the Kuiper Belt, at the very edge of the solar system billions of miles from the Sun. This prompted some astronomers to suggest that Pluto could be just another Kuiper Belt Object (KBO), disappointing generations of schoolchildren who grew up learning that Pluto was the smallest planet in the solar system
The importance of the components of solar system
Importance of the Components of Solar system
Although the solar system has many components, only the Earth and Sun are most important components of the solar system. This is because the Earth sustains lives of a diversity of living organisms (plants and animals). It contains numerous resources that enable living organisms to survive in it. The Earth’s atmosphere contains water and air that are used by living organisms for survival. In general, Earth is the only planet where both living and non-living organisms can be found. The Sun is the source of all energy that supports life on Earth. The Sun is supports water cycle and facilitates weather conditions and climate
The following are importance of the Sun
- The Sun is very important for growth of the plants. The Sun helps the plants to make their own food by the photosynthesis process.
- The Sun is very necessary for living organisms, as it provides us with light that enable us to do our work.
- The Sun provides us with heat to warm our bodies.
- The Sun provides food to some animals and humans (that feed on plants).
- The Sun is the source of heat used in heating water, warming our bodies
- The Sun is the source of solar energy used in our daily lives.
- TheSunisimportantintheformationofrainfall.Forexample,theSunevaporatesthe water in the seas, lakes and oceans into water vapour. When the water vapourrisesinthesky,itcoolsandcondensesformingtheclouds,whicheventuallyformsrain.
The Sun
The Sun
The Sun is a medium star. It is one of the millions of stars that you see at night in the sky. It looks much bigger because it is closer to the Earth than other stars. The Sun is much larger than the Earth, and much larger than all the other components of the solar system when put together. The Sun is the main source of energy that the planets receive. It is composed of different gasses; approximately 75% hydrogen, 23% helium, and 2% for all other elements. The Sun is so hot that nearly all molecules are broken into their separate atoms and all are mixed together into a single hot gas
Describe the characteristics of the Sun
The diameter of the Sun is 1.392 million kilometers. Its mass is approximately 330,000 times greater than that of the Earth. The Sun shines brightly because of its very high temperatures. The average surface temperature is 6,000 degrees Centigrade. It is much hotter in the interior where it is about 14 million degrees Centigrade
The Sun contains 99.85% of all the matter in the Solar System. The planets, which condensed out of the same disk of material that formed the Sun, contain only 0.135% of the mass of the solar system. Jupiter contains more than twice the matter of all the other planets combined. Satellites of the planets, comets, asteroids, meteoroids, and the interplanetary medium constitute the remaining 0.015%.
Solar energy
The Sun is the source of all energy on Earth. This energy is known as solar energy
Define the term solar energy
Solar energy can be defined as the radiant (light and heat) energy produced by the Sun
Uses of Solar Energy
Solar energy has been used for thousands of years in many different ways by people all over the world. The following are the uses of solar energy in everyday life
1 Generation of electricity: Solar energy generates electricity by the use of solar panels. Solar energy is captured by solar panels for different purposes. The electricity generated can be used in supplying power for different machines, devices and home appliances (Figure 2.2
- Heating, cooking and drying: Solar energy is used in heating, cooking, drying clothes, meat, fish, fruits and grains etc. For example, a solar cooker which traps heat from the Sun can be used for cooking food.
- Photosynthesis: Solar energy support growing plants in making their own food through the processes of photosynthesis.
- Formation of rainfall: Heat from the Sun causes liquid and frozen water to evaporate into water vapour gas, which rises high in the sky to form clouds and finally fall as rainfall.
- It provides vitamin D essential for the body skin: The Sun is the source of vitamin D.
- It helps in the production of salt from sea water and lakes: The process of harvesting salt from sea water involves evaporation of sea water in evaporation ponds or tanks. As water evaporates, it leaves the salt in tanks or ponds, from which it is collected and processed further before use(figure2.3)
The use of solar energy promotes environmental conservation.
Solar energy is one of the safe sources of energy in the world. This is because it does not produce pollution to the environment during its use. It is a safe source of energy and environmental friendly. The following points explain how solar energy promotes environmental conservation
- Solar energy does not release carbondioxide gases into the atmosphere to deplete the ozone layer.
- The use of solar energy reduces the demand for charcoal and firewood as a source of energy in our households. This reduces the cutting down of trees, which could other wise lead to environmental degradation.
- The use of solar energy encourages the preservation, conservation and sustainable utilization of forest resources.
- Reduced use of firewood means retaining more trees that could be cut down for fire wood. Trees, in turn, absorb excessive carbondioxide from the air, thus helping to purify the air and balance the gases in the atmosphere.
- Solar energy is used by plants during photosynthesis to produce glucose and release oxygen into the atmosphere.
- Solar energy reduces dependency on kerosene and spirit which burn to produces smoke that pollutes the environment.
- Solar energy is a renewable source of energy. It is obtained daily during sunshine and it is permanent and reliable (Figure 2.4).
Solar energy contribution to emancipation of women.
In African societies, the task of fetching firewood (figure 2.5), cooking, washing, and taking care of children falls mainly under women and girls. The use of solar energy for cooking, heating and performing other household duties, means allowing more free time for women and girls from the burden of fetching and carrying firewood. This creates more time for, women and girls to participate in other income-generating activities such as trade and farming. On the other hand, girls will attend schools and perform as better as boys do.
Also, the use of solar energy instead of firewood will contribute to the improvement of the women’s health. This is because they will not be exposed to soot, ashes and smoke generated by firewood when burnt. Therefore, the use of solar energy in performing different household duties will contribute to emancipate both women and girls make their lives easy
The Planets
Planets are bodies revolving around the Sun (mentioned in the previous section). Planets revolve around the Sun in an anticlockwise direction following paths called orbits. As they revolve around the Sun, they appear to move among the stars. This is the reason why the Greeks called them the planets, which in their language means wandering stars
All the light and heat of the planets come from the Sun. Hence, the temperatures on the planets depend on their relative distances from the Sun. All planets revolve around the Sun in the same direction in orbits that are elliptical and nearly in the same plane
Each planet has its own orbit and takes a different length of time to complete one revolution around the Sun. Mercury is closest planet to the Sun and it takes the shortest period of time to complete one revolution. On the contrary, Neptune is furthest from the Sun takes the longest time. Table 2.1 shows the distances of planets from the Sun and the time taken by a given planet to complete one revolution (orbit) around the Sun
Location of the planets in the solar system.
Distances of planets from the Earth.
Other bodies in the Solar system
Apart from the planets, there are other heavily bodies that are found in the solar system. Most of these bodies are much smaller than the planets and some of them revolve around the planets. These include comets, asteroids, meteors, and natural satellites
Characteristics of comets, asteroids, meteors, and satellites.
Comets
Comets are objects with leading heads and bright tails in the sky. Sometimes they can be seen at night. They are composed mainly of rock, ice, dust and frozen gases. A combination of all of these components gives the comet a shiny appearance. As the comet passes near the Sun, it leaves a trail of dust. Comets orbit around the Sun far beyond the limits of Pluto. They can be seen from the Earth only when their orbits overlap that of the Earth. This is because other times their orbits are very far away
Asteroids
Asteroids are solid heavily bodies revolving around the Sun but are too small to be called planets. Tens of thousands of these minor planets are gathered between the orbits of Mars and Jupiter. The largest asteroid has a diameter of less than 800 kilometers. These bodies can only be seen with a telescope because they are very far away from the Earth
Asteroids are found in a portion of the solar system called asteroid belt. As the name suggests, this is a belt where asteroids are most likely to occur. The largest of the existing asteroids is called Ceres, with a diameter of approximately 930 kilometers
Meteors
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 kilometers above the Earth’s surface. As a result of friction with the atmosphere, they become hot and usually disintegrate. But when meteors do not disintegrate completely in passing through the atmosphere, it reaches the Earth’s surface as large bodies known as meteorites. These bodies are usually made of nickel, iron and silica. Sometimes meteors reach the Earth’s surface with such a force that they make large holes or craters called meteor craters
Natural satellites
A natural satellite is an astronomical body that orbits a planet or minor planet. The largest known satellite is the moon. Other planets also have large moons, e.g., Jupiter’s Galilean moons (Ganymede, Callisto, Io and Europa), Saturn’s moon (Titan) and Neptune’s moon (Triton)
Four dwarf planets including Pluto, Haumea, Makemake and Eris are also known to have natural satellites: Pluto (Charon, Hydra, Nix, Kerberos, and Styx); Haumea (Hiʻiaka and Namaka), Makemake [S/2015 (136472) 1]; and Eris (Dysnomia). As of January 2012, over 200 minor-planet moons have been discovered
Most of the 178 known natural satellites are irregular moons, while only 19 are large enough to be round. Ganymede, followed by Titan, Callisto, Io and Earth’s Moon are the largest natural satellites in the solar system. Figure 2.7 shows some of the natural satellites found in the solar system
Narrate local incidents linked to meteorites.
There are two known meteorites in Tanzania. One is found in Mbozi district in Mbeya region and another is in Malampaka in Kwimba district of Mwanza region. These meteorites fell from space and reached the Earth in 1930 and they formed large holes on the Earth’s surface
Shape of the Earth
Earth
Earth is the third planet from the Sun. It is the only planet known to have an atmosphere containing free oxygen, oceans of liquid water on its surface, and support life. About three quarters (¾) of the Earth’s surface is coved by water.
Earth is the fifth largest of the planets in the solar system, smaller than the four gas giants planets namely Jupiter, Saturn, Uranus and Neptune, but larger than the three other rocky planets, Mercury, Mars and Venus.
Describe the shape of the earth and its evidence.
The Earth is not perfectly round. Its shape is spherical. The following section provides evidences which prove that the earth is spherical in shape.
Evidence which proves that the Earth is spherical in shape
There are many ways to prove that the Earth is spherical. The following are some of them
- 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 around 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. If you travel in an airplane in a straight path, flying non-stop, you will eventually come back where you started your journey. This is what is called circumnavigation.
- 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 aspherical body.
- 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 the harbour, its disappearance over the curved surface is equally gradual. If the Earth is flat, the entire ship would be seen or obscured all at once
- 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 is flat, the whole world would have Sunrise and Sunset at the same time. But we know this is not the case
- 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
- 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
- Driving poles on level ground on the 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. Surveyor sand field engineers, therefore, have to make certain corrections forth is inevitable curvature,i.e.12.6cm to1km.
- 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 is spherical
Earth’s Movement
The Earth is in motion all the time. People cannot feel this motion because, like all other planets, they move with it. There are two types of movements of the Earth.
Describe the types of earth’s movements.
There are two types of movements of the Earth, namely
- The rotation of the Earth on its own axis.
- The revolution of the Earth a round the Sun
Describe the term rotation.
Rotation refers to the spinning of a body on its axis. The Earth rotates or spins on its axis in an anti-clockwise direction, from West to East through 360 degrees. It makes one complete rotation 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 North (N) and South (S) poles through the centre of the Earth. The rotation of the Earth is very rapid although it is difficult to feel its motion. At the equator, every point of the Earth’s surface is travelling eastwards at about 1600 km per hour. At latitude 40 degrees, the speed is about 1280 km per hour
The Earth’s axis makes an angle of 66 ½ degrees with the plane of its orbit. In other words, the axis is tilted 23 ½ degrees from the perpendicular
Evidence to prove that the earth rotates.
The following observations illustrate that the Earth rotates from West to East The following observations illustrate that the Earth rotates from West to East
- When travelling in a fast-moving vehicle, you notice that trees and other objects on both sides of the road are moving fast in the opposite direction. This observation is similar to the movement of the Earth in relation to the Sun.
- At night most of the stars appear to move across the sky from West to East. This observation shows that the point of observation (Earth) is moving from West to East
- Sunrise and Sunset: the Sun rises over the eastern horizon in the morning and sets over the western horizon in the evening. But since the Sun is in the Centre of the solar system and the fact that it does not move, this shows that the point of observation (the Earth) is moving by rotation from West to East
- Day and Night: During the Earth’s rotations some regions face the Sun while others do not face it. The regions facing the Sun experience day time whereas the regions which are not facing the Sun are in darkness (night). If the Earth is not rotating, one half of the Earth would be having daylight while the other half would be in total darkness forever. The occurrence of day and night proves that the Earth is rotating
- Photographs of the Earth taken from the satellite at different times of the day show that different parts of the Earth experience daylight at different times
- If the Earth is not rotating, different photographs taken at any time of the day would all look alike
The significance of the Earth’s rotation.
The rotation of the Earth is very important because it causes the following phenomena
- Alternation of day and night: Rotation of the Earth causes the side 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). This ensures that, at any time of the day, one half of the Earth is in darkness and the other is in daylight. If the Earth did not rotate then one half of it would be in daylight while the other half would be in darkness all the time (Figure2.9)
- The occurrence of tides: Tides are the periodic rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the Sun on the rotating Earth
- Time difference between longitudes: The rotation is causes the difference in time between different places on the Earth. It causes the difference of one hour in every 15degree interval between longitudes, which is equivalent to 4 minutes for each degree of longitude
- Deflection of winds and ocean currents: As the Earth rotates on its axis from West to East, winds and ocean currents flowing over the Earth’s surface are deflected. The anticlockwise rotation of the Earth deflects prevailing winds to the right in the northern hemisphere and to the left in the southern hemisphere
Define the term revolution.
In Geography and Astronomy, the word revolution is defined as the motion of one body around another. The Earth revolves around the Sun while the moon revolves around the Earth.
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 kilometers from the Sun. The Earth is at perihelion each year on 3rd January when it is at the minimum distance of 147 million kilometers (Figure 2.11)
The Earth’s revolution around the Sun takes a year (365¼ days). Therefore, the average 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 results of the Earth’s revolution around the sun
The revolution of the Earth around the Sun and the inclination (tilting) of its axis results in the following
- The four seasons of the year, namely summer, autumn, winter and spring
- Changes in the position of the midday Sun at different times of the year
- It causes 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 an angle of 66.5 degrees. If the axis of the Earth was vertical, the Sun rays would always be overhead at the Equator, thus all places on the Earth would always experience 12 hours of daylight (day) and 12 hours of darkness (night).
- The eclipses (Eclipse of the Sun and eclipse of the moon).
Four Seasons
Because of the inclination of the Earth’s axis to the orbital plane, the angle at which the Sun rays shrike the Earth’s surface varies. This leads to seasonal changes which are mainly experienced in the high and mid-latitude regions. This results in four distinct seasons namely, spring, summer, autumn and winter.
Change in the Position of the Midday Sun
Because of the inclination of the Earths’ axis, the midday Sun is directly overhead at the Tropic of Cancer on 21st June; and at the Tropic of Capricorn on 22nd December. This is called the solstice. On 21st June, it is winter solstice in the southern hemisphere and summer solstice in the northern hemisphere. On 22nd December, it is winter solstice in the northern hemisphere and summer solstice in the southern hemisphere. On 21st March and 23rd September, the midday Sun is directly overhead at the Equator. These are the only two days in the year when all places on Earth have almost equal hours of day and night. This is known as the equinox.
Table 2.2 shows dates on which the Sun is vertically overhead at the Tropic of Cancer, Tropic of Capricorn and the Equator. The resulting seasons are also indicated
Varying Lengths of Day and Night
Not all places across the Earth experience the same lengths of day and night. Some places receive long hours of daylight than darkness while others receive long hours of darkness than daylight. This is because the Earth’s axis is inclined at 66 ½ degrees to the orbital plane (23 ½ degrees to the perpendicular). The Earth remains permanently inclined at this angle as it revolves around the Sun
If the Earth’s axis was perpendicular to its orbital plane, all places on the Earth’s surface would have equal days of daylight and darkness throughout the year. In December, it is winter in the southern hemisphere and the hours of darkness increase steadily. The further away a place is from the equator, the longer the nights. Usually, beyond the Arctic Circle which is 66½ degrees North towards the North Pole the number of days of complete darkness increases. The North Pole is in complete darkness for half a year.
Eclipses
Eclipse refers to the partial or complete obscuring of one celestial (heavily) body by another. An eclipse occurs when one celestial body moves in between another heavily body and its source of light (the Sun). Eclipses normally occur when the Sun or moon is obscured from the view for a short period. This means that an eclipse will only occur when the Sun, moon and Earth are in a straight or nearly straight line.
The question is how the eclipses related to the revolution of the Earth? The answer is that as the Earth revolves around the Sun and the moon revolves around the Earth, there comes a time when the moon and the Earth are in a straight line. As a result, an eclipse of the moon (lunar eclipse) or the Sun (solar eclipse) occurs, depending on which body (the Earth or the moon) causes an obstruction
Lunar eclipse
This eclipse occurs when the Earth passes between the moon and the Sun and the Earth’s shadow falls on the moon
Solar eclipse
A solar eclipse occurs when the Moon passes between the Earth and the Sun, thus casting its shadow onto the Earth. In this type of eclipse, the Moon fully or partially blocks the Sun, leading to total or partial eclipse respectively
Importance of the parallels and meridians.
Define the parallels and meridians
Parallels are more commonly known as latitudes. Latitude refers to an angular distance North or South of the equator adjusted in degrees, minutes and seconds, measured from the Centre of the Earth. The equator is given a value of 0 degrees. It is an imaginary line which divides the Earth into two hemispheres (Northern hemisphere and Southern hemisphere). The Northern hemisphere has latitude of 90 degrees North and the Southern hemisphere has latitude of 90 degrees South. All other latitudes are drawn north or south, parallel to the equator. Particular latitude, for example, 60 degrees North, joins all points on the surface of the Earth which make an angle of 60 degrees from the Centre of the Earth (the equator). Any circle drawn around the Earth, parallel to the equator, is a parallel of latitude. Table 2.3 shows important parallels and figure 1.18 shows the location of these parallels on the Earth’s surface.
Meridians are commonly known as longitudes. Longitude is an imaginary line drawn on the map from the North Pole to the South Pole. Meridians are numbered in degrees East or West of longitude 0°, called Greenwich Meridian (because it passes through a town in England called Greenwich). It is also known as the Prime Meridian because it is the line of reference from which all other meridians are established
A longitude, therefore, refers to an angular distance measured in degrees East and West of the Greenwich Meridian. The Prime Meridian runs through the poles and the Greenwich observatory near London. All lines of longitude are in equal length and divide the Earth into two equal semi circles. There are 360° in a circle, with 180° lying east of the Greenwich Meridian and the other 180° west of Greenwich. The Greenwich line has been chosen by convention (meaning that any other line could have served the same purpose)
Describe how latitudes and longitudes are determined.
All latitudes are determined in reference to the equator (0°) The angle of latitude is determined by measuring angles from the Centre of the Earth and from the equatorial plane towards the North or South Pole. It is stated in degrees north or south of the equator, for example 30°S, 15°N, 45°N, etc.
The angle of longitude is determined by measuring the angle from the centre of the Earth, along the equatorial plane towards the East or West of Prime Meridian. The value of latitude is expressed as the angle between the Prime Meridian and the point on any latitude East or West of the Prime Meridian, for example 45°E, 30°W, etc.
The importance of a Great Circle
Great circles
A Great Circle is any circle that circumnavigates the Earth and passes through the Centre of the Earth. A great circle always divides the Earth into halves. Thus, the Equator is the only latitude that is a great circle since it divides the Earth into two equal halves; and all lines of longitude are great circles. More great circles can be drawn around the Earth so long as they pass through the Centre of the Earth and that they divide the Earth into two equal halves
Importance of Great Circles
The shortest distance between any two points on the Earth lies along a great circle passing through the two points. For this reason, great circles are used in plotting routes for ships crossing large stretches of ocean water and aircrafts flying great distances in space. Captains and pilots of ships and aircraft, respectively travel by following great circles in order to save fuel and time because by following the great circle they travel the shortest possible distance to reach their destinations
The importance of parallels and meridians.
The importance of longitudes and latitudes include the following
- They are used by pilots and sailors to guide their paths as they steer the planes and ships
- When used together, longitude and latitude define a specific location through geographical coordinates each location on Earth has its unique latitude and longitude. For example, the location of a point ‘P’ shown in Figure 2.20 below is 40°N, 60°W.
- Longitudes enable geographers to calculate the local time of a place, X, given the local time and longitude of place Y, as the point of reference.
- Latitudes are used as a guide to explain the variation in climate on the surface of the Earth. It is generally known that places in the equatorial belt experience a hot and wet climate for most of the year. As you move north or south of the equator, the climate progressively becomes cold. Places at the north and south poles are extremely cold and are covered by ice and snow throughout the year.
Calculate local time.
The Earth rotates on its own axis once every 24 hours (1 day). Since the Earth turns 360°in 24 hours, it turns 1° in 4 minutes (24×60/360 =4 minutes). All places along a give Meridian will experience midday Sun at the same time. The time recorded along a given meridian is known as Local Time. Since longitude 0° is called Prime Meridian or Greenwich Meridian, the local time at longitude 0° is called Greenwich Mean Time (GMT). It is the reference time for all local times across the globe. When it is 12.00 noon on the Greenwich meridian, it will be 1.00 pm at 15°E or 11.00 am at 15°W.
Local mean time can easily be calculated at any place once the longitude is known because if the Earth completes one rotation (360°) in 24 hours, it passes through 15° of longitude in 1 hour, and 1° in 4 minutes
Example 1
Find the local time for Musoma (34°E) in Tanzania, when it is 12 noon for Kinshasa (15° 30’) in DRC
Solution
- Find the difference in degrees of longitude between Musoma and Kinshasa:34°-15° 3’=18° 30’=18.5°
- Find the difference in time; The difference in time between the two places is 18.5/15 which gives 1 hour 14 minutes
- Since Musoma is to the East of Kishasha, its local time should be ahead of that of Kinshasa. Therefore, the local time for Musoma is 12.00 noon plus 1 hour 14 minutes which is 1.14 pm. On the other hand, given the time difference between two places and the longitude of one of them we can calculate the longitudinal position of the second place
Example 2
Kinshasa is 15° 30’E and it is 1 hour 14 minutes behind the time of Musoma. Find the longitudinal position of Musoma
Solution.
- The difference in time between Kinshasa and Musoma is 1 hour 14 minutes.
- The difference in degrees of longitude between Kinshasa and Musoma is; 1hr−14mins/18 0 30 = 74/4
- Since the time for Kinshasa is behind that of Musoma, then Musoma must be to the east of Kinshasa. Therefore, the longitudinal position for Musoma=15° 30’+18° 30’ =34°E. We can also find the time and longitudinal position of two places located on either side of the Greenwich meridian
Example 3, The local time for a place, X, located 10°W is 11 am. Find the local time for a place, Y, located 5°E.
Solution,
- Find the difference in degrees of longitude between X and Y: 10° + 5° = 15°
- Find the difference in time ;- The difference in time between the two places is which gives1hour
- Since Y is to the east of X, its local time should be ahead of that of X. Therefore, the local time for Y is 11.00 am plus 1 hour, i.e., 12.00 noon
Defining time and time zone.
Time refers to a period that is used for an activity. It is normally measured in seconds, minutes, hours, days, weeks, months, years, decades, centuries or millenniums. A time zone refers to a zone where standard time is accepted throughout a longitudinal zone 15° in width.
The essence of time and time zones.
There would be problems in telling time if every place had its own time set according to the local time. For example, there would be great confusion in railways and airways timetables or radio programmes if they had to show different times, each referring to one particular place within a small area. In order to avoid this problem, different stretches of land take their time from agreed meridians. The time adopted is known as standard time. For example, Tanzania, Kenya, Uganda, Ethiopia, Djibouti and Somalia use the same standard time. This is commonly referred to as the East African Standard time. In East Africa, standard time is taken from 45°E. When a whole stretch of land keeps the same standard time, that stretch forms a time zone. Standard time is the time of the longitude (meridian) near the Centre of the time zone
Variation of standard time in a single country
There are 24 time zones in the world. The Greenwich Meridian (GMT) is the starting point for dividing the globe into 24 time zones. The standard time for Greenwich is known as Greenwich Mean Time. Countries with large stretches of land like Canada, USA, and Russia have several time zones. They have different standard times for different regions within the same country
Define International Date Line.
The International Date Line is the line where a date is changed or where the calendar day begins. This line roughly follows the 180° meridian east (or west) of Greenwich. It is also known as the line of demarcation
When you cross the International Date Line from east to west you lose a day, and if you cross the line from west to east you gain a day. If at Greenwich it is noon on Tuesday, a place 90°W would be 6.00 am on Tuesday; at a place 180°W it would be midnight on Monday. On the other hand, a place 90°E would be 6.00 pm on Tuesday and at place 180°E it would be midnight on Tuesday.
The International Date Line established in 1884 passes through the mid-Pacific Ocean and roughly follows a 180° longitude. It is located halfway around the world from the prime meridian (0° longitude) established in Greenwich England, in 1852. Greenwich is the reference point of time zones. The line zigzags at some points to enable all parts of a country to keep the same date. If the line was to cross a country, island or groups of islands belonging to the same country, then that country would record two different dates on the same day. This problem was avoided by diverting the line at some points (Figure 1.25).
Locate International Date Line.
Chapter Summary
The solar system is made up of the Sun, planets, moons, natural satellites, asteroids, meteors, comets, dust, ice, and interplanetary space containing interplanetary dust and interplanetary gas. All planets and other bodies revolve around the Sun which is the central body of the solar system. The Sun is a medium star. It is the source of all energy on Earth.
Uses of solar energy include generation of electricity, heating, cooking and drying, photosynthesis, formation of coal and oil, formation of rainfall, production of vitamin D in the skin, and production of salt from sea water.
The eight planets include Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune that revolve around the Sun. Each planet has its own orbit and takes a different length of time to complete one revolution around the Sun.
Other bodies in the Solar System include comets, asteroids, meteors and natural satellites. The Earth is the only planet known to have atmosphere containing free oxygen, oceans of liquid water on its surface and support life. The shape of the Earth is spherical.
The two movements of the Earth are the rotation of the Earth on its own axis and revolution of the Earth around the Sun.
Significance of the Earth’s rotation includes alternation of day and night, the occurrence of tides, deflection of winds and ocean currents, and time difference between longitudes.
The effects of revolution around the Sun include four seasons of the year, change in position of the midday Sun at any place and at different times of the year, varying lengths of the day and night at different times of the year, and the eclipses.
The angle of latitude is determined by measuring angles from the centre of the Earth and from the equatorial plane towards the North or South Pole
The angle of longitude is determined by measuring the angle from the centre of the Earth, along the equatorial plane towards the East or West of Prime Meridian.
A difference in longitudes between two places on the Earth’s surface is used to calculate the difference in time between them.
Revision Questions
Question Time 2
1. The following are multiple choice items. Choose the most correct answer from each item and circle it
i. The imaginary line on the Earth’s surface, which closely follows the 180º meridian, is called the
- International Date Line
- Tropic of Cancer
- Prime Meridian
- Tropic of Capricorn
ii. A combination of the Sun and planets together with other heavily bodies are called
- solar eclipse
- lunar eclipse
- revolution
- solar system
iii. The is the only body in the solar system that generates its own heat and light
- Sun
- Moon
- Planet
- Star
iv. Uses of solar energy include
- Drying clothes and grains,and photosynthesis
- Photosynthesis, rainformation, and respiration
- Dryinggrains, photosynthesis, and burning
- Dryingclothes, burning, and photosynthesis
v. Which one of the following statements best describes meteors?
- Piecesof hard matter on Earth that originated from the outer space
- Pieces of hard matter falling from the outer space
- Hard rocks that form large holes on Earth
- Pieces of hard rocks hanging in space
vi. What is the shape of the Earth s?
- Round
- Cylindrical
- Spherical
- Flat
vii. Due to the elliptical shape of the Earth’s orbit, there is a period when the Earth is close to the Sun and when it is far away from the Sun. When the Earth is nearest to the Sun, this is called
- Aphelion
- Maxima
- Perihelion
- Revolution
viii. Days and nights are a result of
- Rotation of the Earth around its orbit
- Revolution of the Earth around its orbit
- Rotation of the Earth on its own axis
- Revolution of the moon around the Earth
An important announcement was broadcast from London by the BBC Swahili Service at 3.40 pm GMT. This was picked up by the navigator of a ship anchored off the coast of Dar es Salaam in longitude 45° E. What was the local time for the ship?
- 12.40am
- 6.40am
- 4. 25 pm
- 6.40 pm
x. Which of the following planets has the longest orbit around the Sun?
- Saturn
- Mars
- Neptune
- Jupiter
xi. The rotation of the Earth is NOT the cause of
- Day and night
- Seasons
- Deflection of ocean currents
- Increasing inclination of the Sun between Sun rise and Sun set
vii. What does the rotation of the Earth on its axis cause?
- Seasons
- Dayand night
- Eclipse
- Change in altitude of over head Sun
xiii. The time when the midday Sun is overhead on latitude 23 ½°S or 23 ½°N is called
- Solstice
- Aphelion
- Equinox
- Tropic of Capricorn
xiv. At which longitude will it be 2.00 p.m. when it is 11.00 a.m. at 10°W?
- 35°W
- 55°W
- 35°E
- 65°W
xv.The angular distance measured in degrees north and south of the equator is known as .
- Longitude
- Latitude
- Altitude
- Prime meridian
XVI. Which of the following identify the central body of the solar system?
- Planets
- Earth
- Sun
- Orbit
XVII. The spinning of the Earth on its own axis is known as .
- Revolution
- Movement
- Day and night
- Rotation
XVIII. Geography is the study of .
- Soil and the atmosphere
- Human activities and the environment
- Physical environment
- Physical features of the land
XIX. A solar eclipse occurs when ___.
- the Earth passes between the moon and the Sun
- the Sun passes between the Earth and the moon
- the moon passes between the Earth and the Sun
- the Earth, the moon and the Sun are in a straight line
2.Below are matching items. Match an item from column A with a corresponding item from column B
| ColumnA | ColumnB |
| (i)Studyof Earth and its environment |
|
| (ii)Studyofclimate | b. Use of charcoal for cooking |
| (iii)Dam | C. Geography |
| (iv)Determineshumanactivitiese.gfarming | D. Tensional force |
| (v)Tropic ofCapricorn | E. Climate |
| (vi)Keepscelestial bodiesin theirorbits | F. Moon |
| (vii)Aterrestrialplanet | G. 23 ½ °S |
| (viii)Sourceofall energyon Earth | H. Sun |
| (ix)Promotesenvironmentalconservation | I. Spherical |
| (x)Shapeof theEarth | J. Use of solar energy for cooking |
| K. Oblate spheroid | |
| L. Physical feature | |
| M. Jupiter | |
| N. Weather | |
| O. Mars | |
| P. Force of gravity | |
| Q. Man-made feature |
3. In each of the following statements, write TRUE for a correct statement or FALSE for incorrect statement
- The Sun is the largest star.
- The moon revolves around the Earth.
- The Earth rotates on its axis and revolves around the Sun.
- The time when the Sun’s orbit is close to the Earth is known as aphelion.
- The Earth rotates from east to west.
- Geography serves as a link between the natural and social sciences.
- The study of weather and weather forecasting is known as cartography.
- In Latin the word sol means moon.
- The solar system consists of 9 planets.
4. Fill in the gaps in each of the following questions
- The contains99.85% ofall thematterin theSolarSystem.
- takes 225 days to complete one revolution around the Sun.
- The largest known satellite is the____ .
- The is only planet known to have an atmosphere containing free oxygen.
- The two movements of the Earth are revolution and______ .
5. Define the following terms:
- Geography
- Rotation
- Revolution
- Planet
6. In a tabular form differentiate between the planets and stars
7. What is the solar system?
8. List the components of the solar system
9. briefly
- What is solar energy?
- Give four uses of solar energy
- Explain the role of solar energy in environmental conservation
- Explain the role of solar energy in women emancipation
10. Give any 5 facts to prove that the Earth is spherical in shape
11. Differentiate between:
- rotation and revolution of the Earth
- axis and orbit of the Earth
- parallels and meridian
- planet and natural satellite
- equinox and solstice
12. State three effects of the rotation of the Earth
13. Explain any three results of the revolution of the Earth
14. What is a great circle?
15. Describe the importance of parallels and meridians
16. State the significance of the International Date Line
17. What could happen if the Earth does not:
- Rotate on its own axis?
- Revolve around the Earth?
18. Explain how parallels and meridians are used to locate the position of a place on the Earth
References
Bunnet, R.B (2005). Physical Geography in Diagrams for Africa (28th edition). Pearson Education Ltd. Essex
Focus, F.D and Said, S.N (2014). Fundamentals of Geography Form One. Longhorn Publishers. Dar es Salaam
Murray, C. D. and Dermott, S. F. (1999). Solar System Dynamics. Cambridge University Press. London
Mzezele, S. and Kibuuka, P. (2015). Geography In Focus Form One. Oxford University Press Ltd. Dar es Salaam
Tanzania Institute of Education (1986). Geography for Secondary Schools, Book One. NPC – (KIUTA). Dar es Salaam
Tanzania Institute of Education (2003). Geography Course Book for Secondary Schools Book One. Ecoprint Ltd. Dar es Salaam.
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