Chapter 3 - Movements of the Earth in the Solar System PDF

Geography for Secondary Schools Student’s Book Form One Chapter Movements of the Earth...

Geography for Secondary Schools Student’s Book Form One Chapter Movements of the Earth The North Pole is about 1280 kilometres per hour. In the meantime, at the poles, the speed is zero Three (0) kilometre per hour. There are several in the Solar system pieces of evidence which show that the Earth is rotating. These include: Introduction Sunrise and sunset: The Sun is located at the centre of solar system; it does not Our planet Earth is not static. It is constantly in motion, which makes t dikeni in move. Instead, as the earth rotates from nature. This motion affects the Earth as a planet and all other life forms found on it. the West to the East, the Sun appears to Therefore, in this chapter, you will learn about the movements of the Ee thin the solar rise from the East and set to the West. It is system and their effects. Such movements include rotation and revo ution of the Earth. this movement of the Earth which explains Also, you will study about the imaginary lines on the earth’s su Such lines include sunrise and sunset. parallels and meridians. The competencies developed whet you to understand the Day and night: The most apparent evidence natural world and inform many aspects of our daily a I 1so help you to monitor The South Pole of the earth’s rotation is the cycle of day and predict different events of the Earth as a celesti , as well as to plan different Figure 3.1: Earth’s rotation and night. The Earth is a sphere. As it spins on its axis, different parts of the planet activities according to time and seasons of he t PN face the Sun at different times, resulting into daylight in one area and darkness in 1. Explain the concept of the earth’ the other. | SU ibtih < Y' rotation. SF Shape of the Earth: The Earth is not a 2. Explain the importance of the earth’s perfect sphere. It is slightly flattened at the Earth's movement in the st sig rotation in your daily life; =~ poles due to the absence of centrifugal force and strong gravitational pull. Meanwhile 3. Differentiate between theearth’s axis it bulges at the equator because of strong relation to the sun. Based on this scenario, and the earth’s line of perpendicular. Rotation of the Earth centrifugal force and weaker gravitational the one moving is the person in the moving pull. All these factors are caused by unequal car not the trees or objects outside the Evidence of theearth’s rotation rotational speed at the poles and at the vehicle. This is just like the rotation of the equator, respectively. Read from library and other reliable online Earth; it is the Earth that rotates, not the Star Trails: When you look at the night sky, sources andsearch for simulation videos Sun. The term rotation means spinning of stars appear to make a circular movement Search for evidence of the earth’s rotation on the meaning of the earth’s rotation, a body on its axis. An axis of the Earth is an around the North or South Poles, from East from library and other reliable online then make short notes. imaginary line joining the North and South sources. to West. In fact, the stars do not move, this Poles through the centre. The earth’s axis happens because the Earth is rotating on its The earth’s rotation changes from no axis from the West to East. is tilted making an angle of 23¥2° from the How the Earth rotates movement at the poles to very fast perpendicular. The earth rotates on its axis in Time Zones: The division of the Earth into movement at the equator. We do not feel When travelling in a fast-moving vehicle, an anticlockwise direction, from West to East different time zones (24 hours) is based on the motion because we move with it. At the while looking outside, the trees and other through 360° in 24 hours (Figure 3.1). This the earth’s rotation. As the Earth spins on its equator every point of the earth’s surface objects outside the vehicle appear to move axis, different regions experience daylight means that, the earth takes 1 hour to rotate moves eastwards at about 1600 kilometres and darkness at different times. in the opposite direction. This observation through 15°, which is equal to 4 minutes per hour. We do not feel this motion because is similar to the movement of the Earth in for every 1°. Coriolis Effect: The Coriolis Effect causes we move with the earth’s movement at a moving objects, like winds and ocean constant speed. At latitude 40°, the speed currents to curve or be deflected due to TTT I the Earth’s rotation. This effect influences The side that faces the sun experiences the (iii) Gain or loss of a day the direction of wind patterns and ocean light from the sun (day) whereas the side This effect is primarily related to crossing the International Date Line. One will lose a currents. The winds and ocean currents that is not facing the sun at that time is in day when crossing the International Date Line (IDL) from the East to the West, and will in the Northern Hemisphere are deflected darkness (night) (Figure 3.2). Therefore, gain a day when crossing the IDL from the West to the East. International Date Line is to the right, while those in the Southern as the Earth rotates its two parts alternate an imaginary line that runs from the North Pole to the South Pole. It follows Meridian Hemisphere they are deflected to the left. between light and darkness, respectively. 180° except where it crosses land surfaces to avoid confusion. If the Earth would not As such, different places on the earth’s surface experience sunrise, noon and sunset be rotating, there would be neither gaining nor losing of a day while crossing the IDL. ESE Y pe at different times in a day (Figure 3.2). 1. Why do we experience sunrise and (iv) Deflection of winds and ocean currents sunset? The earth’s rotation causes deflection of planetary winds and ocean currents. This means 2. What is the impact of the Earth’s axis that they do not blow and flow straight. The planetary winds and ocean currents are tilting to an angle of 232°? deflected to the right in the northern hemisphere and to the left in the southern hemisphere 3. The sun does not move instead the (Figures 3.3a and b). This is based on Ferrel’s Law, which states that “freely moving Earth moves, explain. bodies are deflected to their right in the northern hemisphere and to their left in the 4. Explain the consequences of the earth’s southern hemisphere from their point of origin”’. rotation to stop suddenly. How would this influence different aspects of 4 on Earth? ~4 Figure 3.2; Day and night 5. Why the speed of the earth’s rs, is zero (0) kilometres reer at the (ii) Differences in time poles? = Rotation of the Earth causes differences in time in places located at different The effects of rotation longitudes. Places on the same longitude have the same time. As the Earth rotates on its axis, different places of the world Usinga flashlight and a globe, demonstrate experience daylight and darkness at how the-earth’s rotation causes day and different times. The difference in time is night. Turn on the flashlight on the globe determined by longitudinal differences to represent the Sun’s light, while you between two or more places. The Earth is rotate the globe to simulate its rotation. 360°, it is divided into 24 time zones, each Then, present what you have observed. with approximately 15 degrees of longitude Polar Easterlies width, such that, each time zone represents Rotation of the earth has the following a one-hour difference in time. For example, effects: if you have two places located in different (i) Day and night time zones, one at a longitude 60° West and Figure 3.3 (a): Deflection of winds due to the earth's rotation The change between day and night is caused the other at a longitude 120° East, they will by the rotation of the Earth on its axis. have a time difference of 12 hours. OO == —C  (v) Tides Ocean tide is the rising and falling of water level in oceans as shown in Figure 3.4. This is caused by gravitational attraction exerted largely by the moon and partly by the Sun upon the rotating earth. The main reason why the gravitational attraction of the moon is greater compared to that of the Sun is that the moon is closer to the Earth compared to the long distance from the Sun. When the Earth, moon, and the sun are in a straight line, ocean water level rises and when the earth, moon, and the sun are not in a straight line, the ocean water level falls. Tides are experienced at different times of the day and at night and in different places on the earth’s surface, because the earth is rotating. Figure 3.3 (b): World map showing deflection of ocean currents Figure 3.4: Low and high tide levels of the ocean water Revolution of the Earth. xplain the factors that affect the deflection of winds and ocean currents. (a) Search for videos, simulation, or 2. What is the importance of knowledge animations from reliable online of deflection of winds and ocean sources on how the Earth revolves currents in your daily life? around the Sun and how the Moon revolves around the Earth; 3. Do tides happen in lakes and rivers, Observe what happens during or just in the ocean? Why? the movements, and record your What is the importance of the low and observation; and high tides to your life? Draw an illustration of what you have observed. The Earth revolves around the Sun winter, respectively. Spring is a short season NP March 21" following its orbit. It revolves around the towards summer while autumn is a short pring Equinox sun in an elliptical path, completing one full season towards winter. revolution in approximately 365% days or Generally, there are four seasons in a year one year. However, a normal year has 365 NP which are differentiated by temperature and days. The fraction days are not counted June 21* December 22" rainfall characteristics. These seasons are Winter Solstice every year but are added once in 4 years Summer Solstice Sun at Tropic summer, autumn, winter and spring. The of Capricorn SP, to make a leap year of 366 days. The leap year occurs once in every four years, when four seasons are more pronounced in areas the month of February has 29 days instead found between latitudes 23° and 662° of 28. The speed of theearth’s revolution is North and South of the equator. Around 0° September 23" about 29.6 kilometres per second which is to 5° North and South of the equator never BE Autumn Equinox estimated from the earth’s travel about 940 experience seasons because throughout the million Kilometres. year the sun is almost overhead. Therefore, Figure 3.5: The four seasons of the year these areas. experience high temperature and rainfall. However, this part experiences (ii) Changes of overhead sun Effects of the earth’s revolution seasonal variations due to differences in The position on Earth where the Sun is directly overhead changes throughout the year The revolution of the Earth around the sun relief. The areas between 5° and 23 2° North due to the tilt of the earth’s axis and its elliptical orbit around the Sun. The overhead sun and tilting on its axis has the following and South of the Equator are characterised appears to move northwards and southwards between latitudes 232°N and 2342 S, that effects: by hot-wet and cold- dry seasons. The is, between the tropics of Cancer and Capricorn. For example, during the summer solstice (i) Seasons of the year North Pole (NP) and the South Pole (SP) in the Northern Hemisphere, the Sun.is directly overhead at the Tropic of Cancer, while A season is the main period of the year are normally very cold throughout the year during the winter solstice, it is directly overhead at the Tropic of Capricorn. The places with a particular type of weather. Seasons and it is difficult to distinguish the seasons south of the Tropic of Capricorn and north of the Tropic of Cancer never experience are caused by the tilt of the earth’s axis and of the year in these regions. overhead sun at any time of the year. This change of overhead sun creates the changing the earth’s revolution around the sun. With In the Northern Hemisphere, summer seasons and variations in daylight hours at different latitudes (Figure 3.6). respect to the orbital plane or the horizontal months are June, July and August. plane, the earth’s axis is tilted at an angle of Autumn months are September, October, 662°. However, with respect to the vertical and November. Winter season occurs in plane, the Earth has an axial tilt of 232°. December, January, and February whereas In its revolution around the sun, one of the spring months are March, April and May. hemispheres is inclined towards the sun at In the Southern Hemisphere, the summer one period of the year and away from sun months are December, January, and February. June 21" at another period of the year. For example, Summer Solstice December 22™4 Autumn occurs in March, April, and May. Winter Solstice in the months of December, January, Winter season in the Southern Hemisphere and February, the Southern Hemisphere occurs in June, July, and August, whereas, tilts towards the sun. Thus, it is summer spring months are September, October, and time. The same months in the Northern November (Figure 3.5). However, due to Hemisphere experience winter season because the Northern Hemisphere tilts away the influence of relief and oceans, these September 23" SP Autumn Equinox from the sun. Spring and autumn are short seasons do not always occur in the basis seasonal transitions between summer and of explained sequence. Figure 3.6: Apparent movement of the overhead sun OE  Solstice and equinox The tilting nature of the earth’s axis causes parts of its surface to receive different 1. Discuss the effects of the earth’s revolution in your area. (a) Design a globe by using locally amount of sunlight at different times of 2. Explain the common economic activities carried out in your area in different available materials to represent the the year. This situation leads to solstice seasons of the year. Earth. Use flashlight to represent and equinox. Solstice comes from the Latin the Sun, then place the globe at an word solstitium, which contains two words: sol the term that means Sun and sistere that angle to represent the Earth’s tilt; means stand still. The solstice, therefore, (b) Turn on the flashlight and shine it 1. Think of your community at home town or village, and relate the seasons of the literally means “‘sun-stand still”. Solstice directly at the centre of the globe, year with their daily activities. Use the following questions for guidance: is a phenomenon that occurs when the simulating the Sun’s rays; earth’s poles are mostly inclined towards or (a) What activities do they conduct in each season? (c) Observe the way light hits the globe (b) Why do you think they do such activities in that particular cease away from the sun, causing the earth’s pole which is inclined towards the Sun to receive and write notes on what you have 2. Write short essay on the activities done in relation to the seasons of the year. maximum sunlight. This makes the most observed in relation to the equinox. inclined pole towards the sun to experience the longest day in the year. During this (iv) Aphelion and Perihelion time, the Sun is vertically overhead in (iii) Varying lengths of day and night at The Earth revolves around the sun in an elliptical orbit. Due to the elliptical shape of respective tropic on specific dates. The different times of the year. the earth’s orbit, the Sun is closer to the Earth at one point of the year than at the other southern hemisphere gets the maximum The lengths of day and night are not the (Figure 3.7). The furthest position from the sun in the orbit of the earth is called aphelion. intensity of the sun’s rays on December Normally, the Earth is at aphelion each yearon 4" July when it is 152 million kilometres same across the world because the earth’s 22™ which is the Summer Solstice in the away from the Sun. Perihelion occurs-when the Earth is nearest to the Sun about 147 axis is inclined to its plane at an angle of tropic of Capricorn. At the same time, it is 66'2°. Had the earth’s axis been vertical to million kilometres away fromthe Sun. The Earth is at perihelion each year on the 3“ the Winter Solstice at the tropic of Cancer. its orbital plane, all the parts of the earth of January. Aphelion and perihelion affect the amount of solar radiation received by The northern hemisphere solstice occurs on the Earth, though their influence on the seasons is much smaller than the axial tilt. The June 21 commonly known as the Summer would have the same duration of days and nights throughout the year. Places along the slight variation in solar radiation due to Earth’s changing distance from the Sun during Solstice at the tropic of Cancer. At the same time, it is winter solstice at the tropic of its orbit is not sufficient to cause significant climate change or shifts in seasons. equator experience nearly equal day and Capricorn. night throughout the year, but northwards The equinox simply refers to equal lengths or southwards towards the poles, the lengths of day and night. Due to the tilting of the of day and night vary with latitude. For earth’s axis, there are only two times of instance, when the overhead sun is in the the year when the sun is directly overhead Northern Hemisphere, the days are longer at noon at the equator. This results into than the nights in that hemisphere. At the equal distribution of sun rays between the Southern and Northern Hemispheres. North Pole (90°N), daylight is experienced The equinoxes occur on March 21“ and for six months without sunset. While at the September 23" every year. The March South Pole (90°S), darkness is experienced equinox is referred to as vernal equinox for six months In contrast, when the in the Northern Hemisphere and autumnal overhead sun is in the Southern Hemisphere, equinox in the Southern Hemisphere. In the days are longer than the nights in the addition, the September equinox is known Southern Hemisphere. Thus, at the South as autumnal equinox in the Northern Pole (90°S), daylight is experienced for six Hemisphere and vernal equinox in the Figure 3.7: Perihelion and aphelion months without sunset. Southern Hemisphere. TC UO_”@W©>@”V(——>£ &£z@«-  ® 5 (v) Eclipses An eclipse is a total or partial obstruction of light from the sun by either the earth or the Pe moon. This occurs when the earth or the moon intercepts light from the sun. There are Waning quarter Waning gibbous Waning a) two types of eclipses: the /unar eclipse and the solar eclipse. fate, 2 (a) Lunar eclipse Sun rays The lunar eclipse is also known as the eclipse of the Moon. It occurs when the Earth an passes between the moon and the Sun, thus casting its shadow on the moon (Figure 3.8). eon NEW FULL Earth MOON ®@ Moon Waxing crescent ©... gibbous Waxing quarter, Figure 3.9: Phasesof the moon Figure 3.8; Lunar eclipse (b) Solar eclipse the sun is completely blocked it forms the of its surface are illuminated by the Sun. shadow called Umbra. The solar eclipse is also known as the The portion of the Moon facing the Sun is eclipse of the sun. It occurs when the moon Tanzania has witnessed solar eclipse in Search for information:from the library lit, while the portion facing away from the passes between the Earth and the Sun. different times. For example, some parts and other reliable online ‘sources about Sun is in darkness. The angle at which we The moon casts its shadow. over the earth of Tanzania witnessed a total eclipse of the phases of the moon. | see the illuminated portion of the Moon (Figure 3.10). Eclipse of the sun is partial the sun on 23" October 1976. In addition, changes depending on Earth’s position in its when only part of the earth is obscured partial eclipses occurred on 19" April 1977 orbit. As the Earth orbits the Sun, the Sun’s by the shadow of the moon. The portion and 14" October 2000. Meanwhile on 1* Phases of the moon light falls on different parts of the Moon’s of the shadow that results when the light September, 2016, a total solar eclipse was The relationship between the earth’s surface, causing the Moon’s appearance to witnessed in Rujewa, Mbarali District in from the Sun is partially blocked is called revolution around the Sun and the phases change over time. As the Moon orbits the Mbeya Region. Penumbra. Moreover, when the light from of the Moon is what gives rise to the Junar Earth, a sequence of phases is observed cycle and the changing appearance of the namely new moon, waning crescent, first Umbra Moon as observed from the Earth. Moon Moon quarter (waxing half), waxing gibbous, develops different shapes or appearances full moon, waning gibbous, last quarter as seen from Earth. It takes 29% days to (waning half), waning crescent (Figure 3.9). complete one cycle to revolve around As the moon revolves around the Earth, its the Earth. The phases are a result of the illuminated part lights the earth during the changing positions of the Moon, Earth, and night. Also, the gravitational force of the Penumbra Sun relative to each other during revolution. moon on the Earth causes tides in the Earth As the Moon orbits the Earth, different parts surface waters. Figure 3.10: Solar eclipse Significance of eclipses have been developed and refined to capture Parallels and meridians and the South Pole has a latitude of 90° Solar and Lunar eclipses are important and analyse eclipses, leading to innovations Position of a place on the earth’s surface can South (Figure 3.11). The most common in many ways, including their scientific, that have applications beyond astronomy. parallels are the Equator (0°), the Tropic of be found by using parallels and meridians. cultural, and historical significance. The Educational outreach: Eclipses capture Traveling on the planet Earth by air, land Cancer (23'2° N), the Tropic of Capricorn following are significances of eclipse: public’s attention and offer excellent (23° S), the Arctic Circle (662° N), the or waterways needs knowledge of the opportunities for science communication Antarctic Circle (662° S). Facilitation of scientific exploration: distance, direction, and position of places Eclipses provide unique opportunities and educational outreach. They inspire you want to go. Also, in order for people for scientists to study celestial bodies and interest in astronomy, space science, and to perform different activities, they need phenomena that are not normally visible. the natural world, fostering a greater enough knowledge of the places where the During a solar eclipse, the moon blocks appreciation for scientific inquiry. activities are to be performed. Therefore, it is important to study about parallels and ae the sun’s bright disk, revealing the sun’s Environmental effects: Eclipses can have outer atmosphere (corona) and allowing observable effects on the environment. For meridians which are imaginary lines that researchers to gather valuable data about example, during asolar eclipse, the sudden create a coordinate system on the earth’s its composition and behavior. Lunar decrease in sunlight can lead to changes surface, aiding in locating specific points eclipses also offer insights into the Earth’s in temperature and animal behavior. and defining geographical positions. Tropical Capricorn 23%°S atmosphere and its effects on sunlight These effects provide researchers with passing through it. opportunities to study how living organisms Astronomical discoveries: Historically, respond to temporary changes in light and temperature. (a) Take a ball and draw a horizontal eclipses have facilitated significant line that divides the ball into two Figure 3.11: Latitudes discoveries in astronomy. For example, Global interrelationship: Eclipses are equal halves, the hemispheres. observations of the bending of starlight events that people all around the world during a solar eclipse confirmed Einstein’s may witness and share, fostering a sense of (b) Draw another line that divides the (b) Longitudes theory of general relativity. Eclipses global connection and unity. The ability to ball into two equal halves, vertically Longitudes are also known as meridians. have also enabled scientists refine their experience the same celestial phenomenon connecting top and bottom sides of They are angular distance measured in understanding of planetary orbits, lunar from different locations on Earth has the the ball. degrees West or East of the Prime Meridian. features, and other celestial phenomena. potential to bring people together. (c) Add more lines that circle the ball They are imaginary lines which run from Cultural and mythological significance: horizontally and vertically. the North Pole to the South Pole East or Eclipses have often been interpreted through (d) Name the horizontal and vertical West of the Greenwich meridian (0°). The cultural and mythological lenses. They lines you have drawn in relation to Greenwich meridian is the prime meridian feature prominently in various cultures’ 1. How many solar eclipses can be seen parallels and meridians. which passes through the Greenwich creation stories, folklore, and religious in a year? Why? Observatory Station near London where it beliefs. Eclipses can evoke a sense of 2. How do natural surroundings respond (a) Latitudes derives its name. In Africa, it passes through wonder and mystery, leading to cultural to a total solar eclipse? Accra in Ghana. Latitudes also known as or parallels are celebrations, rituals, and narratives that imaginary lines parallel to the Equator 3. Whatare significances of the eclipses? The prime meridian divides the earth into have been passed down through generations. joining all the places at an equal angular East and West. Since there are 360° in the 4. State three assumptions on the effects Technological advancement: The study measurement. The equator divides the Earth sphere, meridians of 0° to 180° lie east of of eclipses? of eclipses has driven advancements in into two equal parts called hemispheres. the Greenwich meridian and the other 0° to various observational tools and techniques. 5. Why does the moon appears in The two hemispheres are the Northern 180° west of Greenwich. Meridians are also Telescopes, cameras, and other instruments different shapes? Hemisphere and the Southern Hemisphere. characterised by the lines of uniform length, The North Pole has a latitude of 90° North, and the width between lines decreases as EOE they converge towards the poles. Figure 90° Since longitude lines meet at the poles, the Great circles 3.12 shows how the meridians look like. distance between degrees of longitudes A Great circle is any circle that divides the North Pole becomes progressively less towards the Earth into two equal spheres (Figure 3.15). poles (Figure 3.14). The equator and the Greenwich Meridian are both great circles. Similarly, all other meridians are also great circles. The equator, SS on the other hand, is the only latitude that is a great circle. Figure 3.13(a): Determining latitudes South Pole North Pole Figure 3.12: Longitudes Determining latitudes Latitude is the distance measured in angles Figure 3.14: Determining longitudes of any point North or South of the equator at which a perpendicular line is established Generally, when locating or finding position. from the centre of the Earth towards the of a place using latitudes, you start with the North Pole or the South Pole (90°), Any latitudes followed by longitudes. angular measurement from the earth’s Great Circles Globe centre to its surface represents certain latitude (Figures 3.13a andb). The distance Figure 3.15: Great circle South Pole from the North Pole to the South Pole is (a) Take the world map or globe, and Great circles are important in our daily life. about 20000 kilometres, and there are 180° find your country on it. Figure 3.13(b): Determining latitudes They are used in navigation and aviation. (half a circle) between them. For example, (b) Study the*latitude and longitude to They are used to plot shore routes for ships the tropic of cancer is drawn on the surface identify the position of your country. crossing the oceans to save fuel and time. In of the Earth with an angular line of 23° N Determining longitudes aviation, pilots use great circles to mark the measured anticlockwise from the equator. A longitude is an imaginary line measured Latitudes are parallel to each other. They shortest path. In general, great circles are from east or west of the prime meridian. result into uniform width between them. the shortest routes between any two places The angle of longitude is determined by They have different lengths, decreasing Explain the relationship between far apart on the earth’s surface. measuring the angle from the centre of from the equator towards the poles. Equator longitudes and time. the earth along the equatorial plane, East is the longest latitude at the centre of the or West of the prime meridian. Since the Why does the distance through the Importance of latitudes and longitudes Earth. Therefore, the distance on the earth’s world is about 40000 kilometres round at Equator from West to East differ from The usefulness of latitudes and longitudes surface between one latitude and the other the Equator and there 360° in a circle, the that measured from North Pole to are as follows: must be equal to 111 kilometres. distance between each degree of longitude South Pole? (a) Latitudes determine climatic variations. 20000 km at the equator must be: Why are parallels different from For example, the temperature = l11km 180° 40000 km meridians? decreases from the Equator towards 360° = Li lkm the poles. 1° of latitude = 111km (b) Longitudes are used to calculate local (ii) When calculating time of two places (iii) Since Mtwara is found in the East of Calculating the longitude ofa place using time of different places on the earth’s located on the same side of the prime Tunis, Mtwara’s time will be ahead local time surface. meridian, for example, East to East of that of Tunis by 2 hours (03.00 pm The longitudes of places are calculated (c) They enable us to precisely identify or West to West, you should find the + 2 hours = 05:00 pm). using their local time. Consider the any location on the Earth. difference in degrees by subtracting following examples. Therefore, the time in Mtwara will the degrees of the two places. (d) They enable us to identify routes for be 05.00 pm when the local time at aviation and navigation. (iii) When calculating the time between Tunis 10° E is 03:00 pm. Example 1 two places located in different sides (e) They help in forming a grid Find the longitudinal position of Mogadishu of the prime meridian, one on the East Example 2 system essential for mapping, and whose local time is 4:40 pm when the local and the other on the West, you should communication of geographic data The local time of Washington, D.C. located time at Libreville, Gabon located at 10° E add the degree of the two places. This worldwide. at 96° W is 05:00 pm Friday. Find the time is 2:20 pm. is due to the rotation of the Earth on its and day at Zanzibar 39° E. Given (f) Longitudes are used to determine days axis. The more you move towards the and dates in the world with reference East, the more time increases, while Given Longitude | Time to the International Date Line. the more you move towards the West Longitude | Time Libreville-Gabon 10° E | 02:20 pm (g) They help to determine distances the more time decreases. The time Washington, DC 96° W_ | 05:00 pm Mogadishu? 04:40 pm between places on the earth’s surface. recorded along the same longitude is Zanzibar 39° E Required known as Local Mean Time (LMT). (pabsttion Consider the following examples. Solution (ij) The difference in time between Calculating local time using longitudes (i) The difference in degrees between Libreville and Mogadishu is given by: The Earth rotates on its own axis from Example 1 Washington, D.C and Zanzibar. will 4:40 — 2:20 = 2:20 hours. West to East once after every twenty four The local time of Tunis located at 10°E is be: 96° +39 ° = 135° (ii) The difference in degrees of longitude hours (one day). This means that the Earth 03:00 pm. What is the local time of Mtwara, turns through 360° in 24 hours. It rotates between Libreville and Mogadishu. Tanzania located at 40° E? (ii) The difference in time between 15° in one hour or 1° in 4 minutes. All the Washington, D.C and Zanzibar will Convert the time difference into Given places along the same longitude experience be calculated as follows: minutes. mid-day at the:same time. For example, if Longitude Time 2 hours 20 minutes = 140 minutes. If 15° = 1 hour it is 12:00 noon in Addis Ababa (39° B), it Tunis (10° E) 03:00 pm Then 135 =? The Earth rotates 1° in 4 minutes, how will also be 12:00 noon in Dar es Salaam Mtwara (40° E) Required many degrees will it take to rotate 140 as it is also located at 39° E. On the T$5° x 1 hour — 9 pours minutes? contrary, places along different longitudes Solution 15° Difference in longitude experience different times. For example, (i) The difference in degrees of longitude (iii) Since Zanzibar is to the East of 140 min x 1° _ 35° when it is 12:00 noon at places like Accra between Tunis and Mtwara will be: Washington, D.C, time will be ahead 4 min in Ghana or London in England located along the Greenwich meridian (0°), it will 40° — 10° = 30° of that of Washington, D.C by 9 hours. (iii) Since the time of Libreville is behind be 1:00 pm at all places along longitude (ii) The difference in time between Tunis Thus, 05.00 pm + 9 hours = 02:00 am that of Mogadishu, then Mogadishu 15°E or 11:00 am along longitude 15°W. and Mtwara will be calculated as Saturday. must be located East of Libreville. While calculating time the following follows: Therefore, the time in Zanzibar will Therefore, the longitudinal position conditions should be observed; If 15° = 1 hour Then 30° =? be 02:00 am Saturday. of Mogadishu will be: (i) Incalculating time, we use longitudes Therefore, 30° x 1 hour = 2 hours 10° E + 35° = 45° E. of given places. 15° Es a Example 2 approximately 15° longitude apart. There What is the longitude of Lindi whose local would be problems in telling time if every time is 08:24 pm when the local time in place had its own time set according to the Montevideo, Uruguay located at 56° W is Local Mean Time (LMT). 02:00 pm? Given Essence of time and time zones, Longitude | Time The essence of time zones resulted Montevideo-Uruguay 56° W | 02:00 pm from difficulties in identifying time for Lindi? 08:24 pm a particular area. If each place across a country followed its own time, it would Solution create confusion. Forexample, Dodoma is (i) The difference in time between Lindi about 35°E and Tanga is about 39°E. If each Figure 3.16: The standard time zones of the world and Montevideo will be: followed its own local time, there would 08:24 — 02:00 = 06:24 hours. be a difference of 16 minutes between the two towns. There would be confusion in (ii) The difference in degrees of longitude between Lindi and Montevideo. railway and airways timetables or in radio programmes if they had different in times, Convert the time into minutes each referring to its local area. 6 hours and 24 minutes = 384 To avoid time confusion, different stretches Since the Earth rotates 1° in 4 minutes. of land take their time from agreed meridian. How many degrees it take to The time adopted is known as standard rotate 384 minute time. In East Africa, standard time is taken Difference in longitu from the meridian of 45°E. When the whole 384 min x1 6g stretch of land keeps the same standard time 4 and that stretch forms a time zone. The Greenwich Meridian is the starting point (iii) sinc-Ano dev of Lindi is ahead of that for dividing the globe into 24 time zones. Pesontevideo, Lindi must be located The standard time for Greenwich is known ast of Montevideo. Therefore, the as the Greenwich Mean Time (GMT). O yrengitade position of Lindi will be: 96° — 56° = 40°E Variation of standard time in a single country z Time zones Countries with large stretches of land, = A time zone refers to a stretch of land where for example, Russia, the United States of = the standard time is accepted throughout America, Canada and China have several :5 the longitudinal zone of 15° in width. The standard time zones for practical purposes Zz world is divided into 24 time zones, each (Figure 3.16). I The International Date Line The International Date Line (IDL) is an imaginary line where date is changed or calendar Name the two most common great circles and explain their importance on the Earth. day begins. This line is internationally agreed upon, and follows the meridian of 180° W (or E) longitude except where it crosses land surface (Figure 3.17). However, the IDL Calculate the longitudinal position keep of town H whose time is 10:00 am, when is not straight for the purpose of avoiding crossing land masses which would cause a it is 3:00 pm in Town G whose longitude is 5° W. country to have two different days at the same time. Calculate the longitudinal position of a town whose local time is 7:00 am while GMT is 5:00 pm. = Kalunde starts his trip at longitude 0° at 12:00 noon-moving towards town Y at longitude 45° E. Calculate the time that Kalunde arrives at his d tination. Tf the time in Town Z located at 75°W is 5:00 pm on Friday, lculate the time and day Town K located at 120° E. ) \ Revision exercise 3_/ 1. “The variation in daytime and night-time ex: erien throughout the day is caused by rotation of the Earth’. Explain. Describe how movements of the E: oon relate in regard to the position of the sun. x, What are the effects of perih:elion aphelion on our life? Why all meridians are great circles? Imagine you are at 5. What i e at 120° E when it is midnight at Greenwich? If iti 4:15 am in a Village A located at 20° E, calculate the local time of a Village located along the following longitudes: 50° E (b) 65°E (c) 75°E (d) 90°E i. If the time at town A located along the meridian 40° E is 10:00 am, calculate the time along the following meridians: Figure 3.17: The International Date Line (a)95° W, (b) 10°W (c) 60° W (d) 0° 10. If the time of town B located at 120° E is 12:00 (noon), calculate the longitude of the following recorded times: Design a pictorial chart giving information of the important parallels and meridians (a) 5:30 pm (b) 5:30 am (c) 12:00 noon = (d) 3:45 pm of the Earth.