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Summary
The Earth is a very big place. To find any spot on it, we use a system of imaginary lines. These lines are called latitudes and longitudes. Together, they create a pattern on the globe called the geographic grid. Think of it like a math graph paper with lines going across and lines going up and down. The lines help us pinpoint any location. A clever Greek thinker named Eratosthenes was one of the first to develop this system.
Lines of latitude are imaginary circles that run from east to west around the Earth. They are all parallel to the Equator, which is the main latitude line right in the middle of the Earth. The Equator is marked as 0 degrees. Latitudes tell us how far north or south a place is from the Equator. Because these lines are parallel, they are also called parallels of latitude. As these lines go towards the North Pole (90 degrees North) or the South Pole (90 degrees South), the circles get smaller. The Equator is special because it’s the largest circle and is called a Great Circle. Other important latitude lines are the Tropic of Cancer and the Tropic of Capricorn, and the Arctic and Antarctic Circles. These lines also help us understand different heat zones on Earth. Near the Equator is the hot Torrid Zone. Further away are the Temperate Zones with milder weather, and near the poles are the cold Frigid Zones. One degree of latitude is always about 111 kilometers.
Lines of longitude are imaginary lines that run from the North Pole to the South Pole. They are also called meridians. These lines tell us how far east or west a place is from a special line called the Prime Meridian. The Prime Meridian is marked as 0 degrees longitude and passes through a place called Greenwich in London. Unlike latitudes, longitudes are not parallel; they all meet at the North and South Poles. Each line of longitude is a semi-circle, and all of them are the same length. When a line of longitude is paired with the one directly opposite it on the other side of the Earth (like the 0-degree and 180-degree lines), they form a Great Circle. The distance covered by one degree of longitude is widest at the Equator (about 111 kilometers) but shrinks to zero at the poles where the lines meet.
Longitudes are very important for understanding time. The Earth spins 360 degrees in 24 hours. This means it spins 15 degrees every hour, or 1 degree every 4 minutes. If you travel east, the time becomes later. If you travel west, the time becomes earlier. This is sometimes remembered with “East-Gain-Add” and “West-Lose-Subtract,” meaning you add time going east and subtract it going west. To avoid every town having a slightly different time, the world is divided into 24 time zones. Countries usually pick a standard time for the whole region. For instance, India uses Indian Standard Time (IST), which is 5 hours and 30 minutes ahead of the time at Greenwich (Greenwich Mean Time or GMT).
The line of 180 degrees longitude, which is on the opposite side of the world from the Prime Meridian, is called the International Date Line (IDL). When you cross this line, the calendar date changes. If you travel east across the IDL, you move into the previous day (it’s like “gaining” a day from the week). If you travel west across it, you move into the next day (it’s like “losing” a day). This “gaining” or “losing” isn’t about actual time disappearing but about the date on your calendar changing. The IDL isn’t a straight line; it zig-zags in some places to make sure a single country or island group doesn’t have two different dates on the same day. Great Circles, like the Equator or a full circle made by two opposite meridians, show the shortest path between any two points on Earth. This is very useful for planning routes for ships and airplanes.
Textbook solutions
Multiple-Choice Questions
1. The imaginary lines running east to west on a globe are called _______ while those running north to south are called _______
(a) Latitude, Longitude
(b) Longitude, Latitude
(c) Equator, Prime Meridian
(d) All of the above.
Answer: (a) Latitude, Longitude
2. Name the criss-crossing lines on a globe that form a framework.
(a) Geographic Framework
(b) Geographic Grid
(c) Geographic Matrix
(d) Geographic Lines
Answer: (b) Geographic Grid
3. Which of the following is true about the lines of Latitude?
(a) They are imaginary lines
(b) They are parallel to the Equator
(c) They reduce in length as we go towards the poles.
(d) All of the above.
Answer: (d) All of the above.
4. Which of the following is true about lines of longitude?
(a) They run parallel to the Prime Meridian.
(b) They are full circles
(c) They are 360 lines at 1° interval.
(d) All of the above.
Answer: (c) They are 360 lines at 1° interval.
5. The distance between two lines of longitude is maximum at which latitude?
(a) Tropic of Cancer
(b) North Pole
(c) Equator
(d) Arctic circle
Answer: (c) Equator
6. The Earth has been divided into how many Time Zones?
(a) 48
(b) 20
(c) 12
(d) 24
Answer: (d) 24
7. What is Standard Time?
(a) Uniform time based on a central meridian.
(b) Time at 0° longitude
(c) Time at 82°30’E
(d) Time at 7½° longitudes at 12 noon.
Answer: (a) Uniform time based on a central meridian.
8. Which of the following is true about the International Date Line?
(a) It goes zig-zag at two points.
(b) The date changes as one moves across it.
(c) It is opposite the Prime Meridian.
(d) All of the above.
Answer: (d) All of the above.
9. A great circle is a circle drawn on the surface of a sphere with radius _______
(a) equal to the radius of the sphere.
(b) equal to half the radius of the sphere.
(c) larger than the radius of the sphere.
(d) less than the radius of the sphere.
Answer: (a) equal to the radius of the sphere.
10. Which of the following are great circles?
(a) Lines of Longitudes
(b) Lines of Latitudes
(c) Equator
(d) Both (a) and (c)
Answer: (d) Both (a) and (c)
11. In each hemisphere for which latitude the length of the circle is half the length of the Equator?
(a) 30°
(b) 45°
(c) 60°
(d) 90°
Answer: (c) 60°
12. The total number of the parallels of Latitude are
(a) 180
(b) 182
(c) 183
(d) 181
Answer: (d) 181
13. The poles are located at what angular distance from the Equator.
(a) 90°
(b) 45°
(c) 60°
(d) 0°
Answer: (a) 90°
14. The length of the Equator is equal to:
(a) 40,075 km
(b) 40,750 km
(c) 40,250 km
(d) 40,525 km
Answer: (a) 40,075 km
15. Which of the following heat zones are correct?
(a) Frigid Zone : 66½°N to 66½°S
(b) Temperate Zone : 90°N to 90°S
(c) Torrid Zone : 23½°N to 23½°S
(d) All of the above.
Answer: (c) Torrid Zone : 23½°N to 23½°S
Short Answer Questions
1. What is a geographic grid? How does the geographic grid serve the same purpose as co-ordinates on a graph?
Answer: The intersection of latitudes and longitudes pinpoint a place on the earth’s surface. These criss-crossing lines form a framework known as the Geographic Grid.
This grid on the globe or the map serves the same purpose as the system of coordinates on the x-axis and y-axis on a graph paper. In this case the x-axis is represented by lines of latitude (horizontal) and y-axis, by lines of longitude (vertical).
2. What are lines of latitude and longitude? Who devised the lines of latitude and longitude?
Answer: The lines running east to west, parallel to the Equator, are called lines of latitude. The lines running north to south passing through the poles are called lines of longitude.
Eratosthenes, the Greek philosopher, who had for the first time calculated the circumference of the earth, had devised lines of latitude and longitude to locate places on the earth.
3. Mention two characteristics of lines of latitude.
Answer: Two characteristics of lines of latitude are:
- Lines of Latitude are the imaginary lines joining all places having the same latitude towards north or south of the Equator.
- Since the lines of latitude are parallel to the Equator and each other, they are called parallels of latitude.
4. Name the two hemispheres of the earth made by the Equator. Name the thermal zones of the earth.
Answer: The Equator that runs midway between the poles divides the earth into two equal hemispheres known as the Northern Hemisphere and the Southern Hemisphere.
The thermal zones of the earth are:
- The Torrid or Tropical Zone: The area lying between the Tropic of Cancer (23½°N) and Tropic of Capricorn (23½°S) mark the limits of the Torrid (meaning very hot) Zone. It is also called the Tropical Zone. It is the hottest zone of the earth.
- The Temperate Zones: Two other important lines of latitude based on temperature are the Arctic Circle (66½°N) and the Antarctic Circle (66½°S). Between the Arctic Circle and the Tropic of Cancer as well as between the Antarctic Circle and the Tropic of Capricorn lie the two Temperate Zones — the North Temperate (23½°N to 66½°N) and the South Temperate zones (23½°S to 66½°S). In this region, the climate is moderate, i.e., neither too hot nor too cold.
- The Frigid Zones: Between the Arctic Circle and the North Pole and between the Antarctic Circle and the South Pole are the two Frigid Zones of the earth. These are the polar regions and receive the sun’s slanting rays. In these two zones, very low temperatures are recorded.
5. List any two uses of the lines of latitude. Express 1° angular distance in kilometres.
Answer: Two uses of the lines of latitude are:
- To find the location of a Place: Latitudes give us the location of a place north or south of the Equator. Such a location is known as an absolute location.
- To measure the distance of a Place: Distances are calculated with reference to the Equator at right angle to the place. We can therefore, measure the distance of any place from the Equator based on its degree of latitude.
The 1° angular distance is roughly equal to 111 km.
6. With the help of a diagram, show the important lines of latitude.
Answer: The important lines of latitude are the Equator (0°), Tropic of Cancer (23.5°N), Tropic of Capricorn (23.5°S), Arctic Circle (66.5°N), Antarctic Circle (66.5°S), North Pole (90°N), and South Pole (90°S).
7. Which line is known as the Prime Meridian? State its importance.
Answer: The Prime Meridian is the line of longitude whose angular distance is defined as 0°. It passes through Greenwich near London.
The Prime Meridian, together with the 180° longitude usually divides the earth into the Eastern and Western Hemispheres. This division holds good practically for all purposes.
8. How can the general climate of an area be described with the help of the lines of latitude?
Answer: Lines of latitude indicate the general climate of the area by applying the principle of heat zones or thermal zones of the earth. Thus, latitudes enable us to divide the whole earth into different climatic zones.
9. Which line of longitude is used to fix the World Standard Time? State its value in degrees. State the longitudinal value in degrees of Indian Standard Meridian.
Answer: The time at Greenwich (0° longitude) has been selected as the mean time and is used to fix the World Standard Time. Its value is 0° longitude. The longitudinal value in degrees of Indian Standard Meridian is 82°30’E.
10. List any two characteristics of the Great Circles.
Answer: Two characteristics of the Great Circles are:
(i) A great circle is a theoretical circle formed by the intersection of the earth’s surface and an imaginary plane that passes through the centre of the earth and divides it into two equal parts.
(ii) All such circles must pass through or touch the centre of the circle.
11. List any two uses of the Great Circles.
Answer: Two uses of Great Circles are:
(i) Navigators use great circles to find the shortest distance between any two points on the earth’s surface. A Great Circle Route is the shortest distance between two places on the earth and lies on the arc of a great circle.
(ii) Great Circle routes are specially important for places that are on opposite sides of the globe. Most globes show great circle routes between distant ports across the Atlantic, the Pacific and the Indian Ocean.
12. What are the Great Circle Routes? State their importance.
Answer: A Great Circle Route is the shortest distance between two places on the earth and lies on the arc of a great circle. Navigators use great circles to find the shortest distance between any two points on the earth’s surface. Great Circle routes are specially important for places that are on opposite sides of the globe. Most globes show great circle routes between distant ports across the Atlantic, the Pacific and the Indian Ocean. Great circles are also used by meteorologists to determine climate and weather conditions in a region.
Structured Questions
1. (a) State the five lines of latitude.
Answer: The five main lines of latitude are:
- The Equator (0° latitude).
- The Tropic of Cancer (23½°N).
- The Tropic of Capricorn (23½°S).
- The Arctic Circle (66½°N).
- The Antarctic Circle (66½°S).
(b) What is the significance of these lines of latitude?
Answer: The lines of latitude form one of the coordinates of the grid system and have the following uses:
- To find the location of a Place: Latitudes give us the location of a place north or south of the Equator. Such a location is known as an absolute location.
- To measure the distance of a Place: Distances are calculated with reference to the Equator at right angle to the place. We can therefore, measure the distance of any place from the Equator based on its degree of latitude. For example, the latitude of Mumbai is 19°N and that of New Delhi is 30°N. We know that 1° latitude = 111 km. We can say that Mumbai is 2109 km (111 × 19°) away from Equator. Similarly, New Delhi is 3,330 km (111 × 30°) away from Equator.
- Heat Zones: Besides helping us to locate places on maps and charts, lines of latitude divide the earth into distinct heat belts. The lines of latitude indicate the general climate of the area by applying the principle of heat zones or thermal zones of the earth. Thus, latitudes enable us to divide the whole earth into different climatic zones.
(c) Give a geographical reason for each of the following:
(i) Lines of latitude are called parallels of latitude.
Answer: Since the lines of latitude are parallel to the Equator and each other, they are called parallels of latitude.
(ii) Lines of latitude are not of equal length.
Answer: The lines of latitude are not of equal length and become smaller as we move towards the poles. At 60° latitude, in each hemisphere the length of the circle is half the length of the Equator. At the poles these lines are just points or dots.
(iii) Lines of latitude carve out the heat zones of the earth.
Answer: Lines of latitude divide the earth into distinct heat belts. The lines of latitude indicate the general climate of the area by applying the principle of heat zones or thermal zones of the earth. Thus, latitudes enable us to divide the whole earth into different climatic zones.
(d) Draw a well labelled diagram showing the different heat zones of the world.
Answer: The different heat zones of the world are the Torrid zone, Temperate zones, and Frigid zones. The Torrid zone lies between the Tropic of Cancer (23.5°N) and the Tropic of Capricorn (23.5°S). The North Temperate zone is between the Tropic of Cancer (23.5°N) and the Arctic Circle (66.5°N), and the South Temperate zone is between the Tropic of Capricorn (23.5°S) and the Antarctic Circle (66.5°S). The North Frigid zone is between the Arctic Circle (66.5°N) and the North Pole (90°N), and the South Frigid zone is between the Antarctic Circle (66.5°S) and the South Pole (90°S).
2. (a) Describe the lines of longitude.
Answer: The lines running north to south passing through the poles are called lines of longitude. A longitude is the angular distance of a place east or west of the Prime Meridian. The Prime Meridian is the line of longitude whose angular distance is defined as 0°, and it passes through Greenwich near London. The lines to the west of Greenwich are suffixed with ‘W’ and those east of Greenwich are suffixed with ‘E’; for example, 60°W and 60°E. There are a total of 360 lines of longitude at 1° interval.
The lines of longitude are also called Meridians of Longitude. ‘Meridian’ is derived from the Latin word ‘meridianum’ meaning noon. The sun crosses a meridian at noon, and all places on a particular meridian will have noon at the same time. All meridians of longitude converge at the poles and are thus of equal length. The Prime Meridian is numbered as 0°, and the others are numbered between 0° to 180°E or W. The line 180°E and W refer to the same meridian and it is diametrically opposite to the 0° longitude. Thus, the 0° and 180° meridian together make a full circle round the earth. Proceeding at 1° interval from both East and West, other full circles will be 1°– 179°, 2°– 178°, 60°– 120° and so on. Of the two lines in any segment, one will be in the east and the other in the west. The sum total of two lines will always be 180°. Individually, all lines of longitude are semicircles. The two diametrically opposite lines make a full circle also known as the Great Circle.
(b) State the use of the lines of longitude in relation to distance and time.
Answer: In relation to distance, the distance between two lines of longitude is maximum at the Equator (111 km). The distance decreases gradually as one moves towards the poles.
In relation to time, lines of longitude are also known as ‘Meridians’. At a particular moment of time, if it is 12 Noon at a given longitude, it must be 12 Noon at all places on this longitude. The Earth makes a complete circle on its axis—it covers 360° longitudes in 24 hours. That is to say, it covers every 15° longitudes in one hour or 1° longitude every 4 minutes. Thus, if it is 12 Noon at 0° longitude, it must be 4 minutes past 12 Noon towards the east at the next 1°E longitude or at 15°E longitude it must be 1 p.m. Towards the west, it will be 1 hour less because the Earth rotates from West to East as the sun first rises in the East. For the purpose of memorising, EGA-WLS formula is used. EGA stands for East-Gain-Add and WLS means West-Lose-Subtract. This in other words means that for each 1° longitude towards the East, 4 minutes are to be added and each 1° longitude towards the West, 4 minutes are to be subtracted. For each degree of longitude, the local time varies by 4 minutes. Lines of longitude are used to find the local and standard time of a place.
(c) Give a geographical reason for each of the following: (i) Lines of longitude are called meridians of longitude. (ii) Lines of longitude are of same length. (iii) Diametrically opposite lines of longitude and the Equator are called Great Circles.
Answer: (i) Lines of longitude are called meridians of longitude because ‘Meridian’ is derived from the Latin word ‘meridianum’ meaning noon. The sun crosses a meridian at noon, and all places on a particular meridian will have noon at the same time.
(ii) Lines of longitude are of the same length because all meridians of longitude converge at the poles and are thus of equal length.
(iii) Diametrically opposite lines of longitude and the Equator are called Great Circles because a great circle is a theoretical circle formed by the intersection of the earth’s surface and an imaginary plane that passes through the centre of the earth and divides it into two equal parts. The Equator and all diametrically opposite longitudes touch the centre of a circle and therefore are Great Circles.
(d) Draw a well labelled diagram to show that places on the same longitude have the same time
Answer: The diagram showing that places on the same longitude have the same time is as follows: Places K, O, and M each have 40° longitude. If it is 12 noon at K, it will also be 12 noon at O and M.
3. (a) State the meaning of the International Date Line.
Answer: The International Date Line (IDL) is the 180° line. When crossing this date line the date changes.
(b) State with an example how time lost or gained is computed with reference to the International Date Line.
Answer: The line of longitude 180° is one and the same for East or West of the Prime Meridian. Since it is diametrically opposite to the Greenwich Meridian it causes a time difference of a full day on crossing the line. The time difference works out to 12 hours (180° × 4 min) from either side. Thus, on crossing the line, a day is gained or lost. When crossing from the east, time will be 12 hours ahead and while crossing from the west time will be 12 hours behind. If it is 8 PM Monday, 25th December at Greenwich, it will be 8 AM Tuesday, 26th December on crossing the 180° line. But if one were to travel from the west, it will be 12 hours behind or 8 AM Monday, 25th December. When the time lost and gained is computed together, the difference works out to full 24 hours at 180°E and W. In the above example, the difference between 8 AM Monday 25th December and 8 AM Tuesday 26th December is 24 hours.
A boat sailing eastwards, when crossing the International Date Line Sunday becomes Monday, so that a day is lost. When another boat sailing westwards crosses the International Date Line Monday becomes Sunday, so that a day is gained.
(c) Give a geographical reason for each of the following:
(i) The International Date Line deviates and goes zig-zag near some islands in the Pacific Ocean.
(ii) The Greenwich time is called the Greenwich Mean Time.
(iii) Great Circles are the shortest routes between two places.
Answer: (i) The International Date Line deviates and goes zig-zag near some islands in the Pacific Ocean to avoid the confusion of having different dates within the same country. The Date Line bends and goes zig-zag at the Bering Strait between Siberia and Alaska and at Fiji, Tonga, New Zealand and some other Islands.
(ii) The Greenwich time is called the Greenwich Mean Time because, while fixing the Time Zones, the time at Greenwich (0° longitude) has been selected as the mean time. The time fixed with reference to Greenwich is called the Greenwich Mean Time or GMT.
(iii) Great Circles are the shortest routes between two places because arcs of great circles are the shortest route between two points on a sphere. Navigators use great circles to find the shortest distance between any two points on the earth’s surface. A Great Circle Route is the shortest distance between two places on the earth and lies on the arc of a great circle.
(d) State with one practical example how is time of a place found with the help of longitudes.
Answer: Time of a place is found with the help of longitudes based on the principle that for each degree of longitude, the local time varies by 4 minutes. For each 1° longitude towards the East, 4 minutes are to be added, and for each 1° longitude towards the West, 4 minutes are to be subtracted.
A practical example of how time is found using longitudes is as follows: The longitude of Mumbai is 73°E and that of New Delhi is 77°E. If it is 12 Noon at Mumbai (73°E), it must be 16 minutes past 12 Noon at New Delhi at the same time. This is because the longitude difference is 77°E – 73°E = 4°. Since 1° longitude equals 4 minutes, a 4° longitude difference equals 16 minutes (4° × 4 minutes). This time is to be added because Delhi lies to the east of Mumbai.
Time-related Questions
1. An important programme was to be broadcast from Mumbai at 7:30 p.m. This was heard by some Indian sailors near Ivory Coast in West Africa at 20°W longitude. What was the local time there?
Answer: To calculate the local time for the Indian sailors near Ivory Coast in West Africa, we first need to determine the time difference between Mumbai and Greenwich Mean Time (GMT), and then between GMT and the sailors’ location.
Mumbai is in India, and the Indian Standard Time (IST) is based on the 82°30’E meridian. India is 5½ hours ahead of GMT.
The programme was broadcast from Mumbai at 7:30 p.m.
So, the time at Greenwich (GMT) when the programme was broadcast is:
7:30 p.m. IST – 5 hours 30 minutes = 19:30 hrs – 5:30 hrs = 14:00 hrs GMT, or 2:00 p.m. GMT.
The sailors are at 20°W longitude.
The Earth rotates 1° longitude every 4 minutes.
So, the time difference for 20°W longitude from GMT is 20 × 4 minutes = 80 minutes, or 1 hour and 20 minutes.
Since the sailors are to the West of Greenwich, their time will be behind GMT. The EGA-WLS formula is used, where WLS means West-Lose-Subtract. For each 1° longitude towards the West, 4 minutes are to be subtracted.
Local time for the sailors = GMT – 1 hour 20 minutes
Local time for the sailors = 2:00 p.m. – 1 hour 20 minutes = 12:40 p.m.
Therefore, the local time for the Indian sailors near Ivory Coast in West Africa was 12:40 p.m.
2. What is the longitude of a place where the local time is 1:15 p.m., when it is 4 a.m. at Chicago (88°W)?
Answer: To determine the longitude of the place where the local time is 1:15 p.m. when it is 4 a.m. at Chicago (88°W), the following steps are taken, based on the principles of geographic grids, latitudes, and longitudes:
Calculate the difference in local time:
The local time at the unknown place is 1:15 p.m.
The local time at Chicago is 4:00 a.m.
The difference in time is 1:15 p.m. (which is 13 hours and 15 minutes in 24-hour format) minus 4:00 a.m. (which is 4 hours and 0 minutes).
So, the time difference = 13 hours 15 minutes – 4 hours 0 minutes = 9 hours and 15 minutes.
Convert the time difference into longitude difference:
The Earth covers 360° longitudes in 24 hours, which means it covers 15° longitudes in one hour, or 1° longitude every 4 minutes.
For the 9-hour difference: 9 hours × 15° per hour = 135°.
For the 15-minute difference: Since 1° longitude is equivalent to 4 minutes of time, 15 minutes is equivalent to 15 minutes ÷ 4 minutes/° = 3.75°.
The total difference in longitude is 135° + 3.75° = 138.75°.
Determine the direction (East or West) of the unknown place relative to Chicago:
The local time at the unknown place (1:15 p.m.) is later than the local time at Chicago (4:00 a.m.).
The EGA-WLS formula is used, where EGA stands for East-Gain-Add. This means that for each 1° longitude towards the East, 4 minutes are to be added to the time. Since the time at the unknown place has been ‘gained’ (it is later), the unknown place is located to the East of Chicago.
Calculate the final longitude of the unknown place:
Chicago is located at 88°W longitude. The unknown place is 138.75° to the East of Chicago.
Starting from 88°W and moving 138.75° towards the East:
To reach the Prime Meridian (0° longitude) from 88°W, one moves 88° East.
The remaining eastward movement required is 138.75° – 88° = 50.75°.
Since this remaining movement is East from the Prime Meridian, the longitude of the unknown place is 50.75°E.
Therefore, the longitude of the place is 50.75°E (or 50°45’E, as 0.75° is equal to 45 minutes).
3. Calculate the time at Durban (longitude 30°E) when the time is 7:00 a.m. at New York (75°W)
Answer: To calculate the time at Durban (longitude 30°E) when the time is 7:00 a.m. at New York (75°W), we follow these steps:
First, we determine the Greenwich Mean Time (GMT) using the time at New York.
New York is located at 75°W longitude.
The Earth covers 1° longitude in 4 minutes.
Therefore, the time difference between New York and GMT is:
75 × 4 minutes = 300 minutes.
Converting minutes to hours: 300 minutes ÷ 60 minutes/hour = 5 hours.
Since New York is to the West of Greenwich, its local time is behind GMT. To find GMT, we add this difference to New York’s time:
GMT = Time at New York + 5 hours
GMT = 7:00 a.m. + 5 hours = 12:00 p.m. (noon).
Next, we calculate the local time at Durban using the GMT.
Durban is located at 30°E longitude.
The time difference between Durban and GMT is:
30 × 4 minutes = 120 minutes.
Converting minutes to hours: 120 minutes ÷ 60 minutes/hour = 2 hours.
Since Durban is to the East of Greenwich, its local time is ahead of GMT, following the principle of East-Gain-Add. To find the time at Durban, we add this difference to GMT:
Time at Durban = GMT + 2 hours
Time at Durban = 12:00 p.m. + 2 hours = 2:00 p.m.
Thus, when it is 7:00 a.m. at New York, the time at Durban is 2:00 p.m.
4. Calculate the longitude of a place where the local time is 6:00 a.m., when the time is 9:00 p.m. at New Delhi on longitude 77°E.
Answer: Time at New Delhi: 9:00 p.m. (which is 21:00 hours in 24-hour format)
Longitude of New Delhi: 77°E
Local time at the unknown place (Let’s call it Place X): 6:00 a.m. (which is 06:00 hours in 24-hour format)
Longitude of Place X: ?
Calculate the time difference between New Delhi and Place X:
Time difference = Time at New Delhi – Time at Place X
Time difference = 21:00 hours – 06:00 hours = 15 hours.
Determine if Place X is East or West of New Delhi:
The time at Place X (6:00 a.m.) is earlier than the time at New Delhi (9:00 p.m.).
Since time is earlier, Place X must be to the West of New Delhi.
(Remember: East Gain Add, West Lose Subtract. If time is less, it’s West).
Convert the time difference into longitudinal difference:
The Earth rotates 360° in 24 hours.
So, 1 hour = 360° / 24 = 15° of longitude.
Longitudinal difference = Time difference × 15°/hour
Longitudinal difference = 15 hours × 15°/hour = 225°.
Calculate the longitude of Place X:
Since Place X is 225° West of New Delhi (77°E):
Longitude of Place X = 77°E – 225°
Longitude of Place X = 77 – 225 = -148°
A negative value when starting from East means we have crossed the Prime Meridian (0°) and are now in the Western hemisphere.
So, -148° means 148°W.
The longitude of the place is 148°W.
5. Calculate the local time at Singapore (104°E) when it is 6:00 p.m. at Greenwich.
Answer: To calculate the local time at Singapore (104°E) when it is 6:00 p.m. at Greenwich, we first need to understand the relationship between longitude and time. The Earth covers 360° longitudes in 24 hours, which means it covers 15° longitudes in one hour, or 1° longitude every 4 minutes.
Greenwich is at 0° longitude. Singapore is at 104°E. Since Singapore is to the East of Greenwich, its time will be ahead of Greenwich Mean Time (GMT).
The difference in longitude is 104°.
For each 1° longitude towards the East, 4 minutes are to be added.
So, the time difference is 104° × 4 minutes/° = 416 minutes.
To convert this to hours and minutes:
416 minutes = 6 hours and 56 minutes (since 416 ÷ 60 = 6 with a remainder of 56).
The time at Greenwich is 6:00 p.m.
Since Singapore is East of Greenwich, we add this time difference to the GMT:
6:00 p.m. + 6 hours 56 minutes.
6:00 p.m. is 18:00 hours.
18:00 + 6 hours 56 minutes = 24:56 hours.
This means it is 56 minutes past midnight, which is 12:56 a.m. the next day.
Therefore, when it is 6:00 p.m. at Greenwich, the local time at Singapore (104°E) will be 12:56 a.m.
6. Calculate the location of a place where the local time is noon when it is 7:30 p.m. at Greenwich.
Answer: Time at Greenwich (GMT): 7:30 p.m. (which is 19:30 hours in 24-hour format)
Longitude of Greenwich: 0° (by definition, as it’s the Prime Meridian)
Local time at the unknown place (Let’s call it Place Y): Noon (which is 12:00 hours in 24-hour format)
Calculate the time difference between Greenwich and Place Y:
Time difference = Time at Greenwich – Time at Place Y
Time difference = 19:30 hours – 12:00 hours
Time difference = 7 hours and 30 minutes.
Convert the time difference entirely into hours: 7 hours 30 minutes = 7.5 hours.
Determine if Place Y is East or West of Greenwich:
The time at Place Y (12:00 Noon) is earlier than the time at Greenwich (7:30 p.m.).
Since time is earlier, Place Y must be to the West of Greenwich.
(Remember: East Gain Add, West Lose Subtract. If time is less/earlier, it’s West).
Convert the time difference into longitudinal difference:
The Earth rotates 360° in 24 hours.
So, 1 hour of time difference = 360° / 24 = 15° of longitude.
Longitudinal difference = Time difference (in hours) × 15°/hour
Longitudinal difference = 7.5 hours × 15°/hour
Longitudinal difference = 112.5°
Since Place Y is 112.5° to the West of Greenwich (0°), its longitude is 112.5°W (or 112° 30′ W).
7. What is the time and day at Mumbai (73°E) when it is Sunday 10:30 p.m. at Shillong (92°E)? Give a reason to support your answer.
Answer: To determine the time and day at Mumbai (73°E) when it is Sunday 10:30 p.m. at Shillong (92°E), we first find the difference in their longitudes.
The longitude of Shillong is 92°E.
The longitude of Mumbai is 73°E.
The difference in longitude is 92°E – 73°E = 19°.
The Earth covers 1° longitude in 4 minutes.
Therefore, the time difference between Shillong and Mumbai is 19 × 4 minutes = 76 minutes, which is equal to 1 hour and 16 minutes.
Since Mumbai is to the west of Shillong, the time in Mumbai will be earlier than the time in Shillong. We apply the principle that for each 1° longitude towards the West, 4 minutes are to be subtracted.
The time at Shillong is Sunday 10:30 p.m.
Subtracting 1 hour and 16 minutes from Shillong’s time:
10:30 p.m. – 1 hour = 9:30 p.m.
9:30 p.m. – 16 minutes = 9:14 p.m.
So, the time at Mumbai will be 9:14 p.m.
The day at Mumbai will be Sunday.
Reason: The Earth rotates from West to East, so the sun first rises in the East. For each 1° longitude towards the West, 4 minutes are to be subtracted. Since Mumbai (73°E) is to the west of Shillong (92°E), its local time will be earlier than Shillong’s local time by an amount calculated from their longitudinal difference (19° × 4 minutes = 76 minutes).
Thinking Skills
1. Find the latitude of your city and state how has this influenced the climate of your city.
Answer: The latitude of my city, Mumbai, is 19°N. This places it within the Torrid Zone, which lies between the Tropic of Cancer and the Tropic of Capricorn. Because of this, Mumbai experiences a hot and humid climate throughout the year, receiving direct sunlight for most of the year. The proximity to the Equator results in high temperatures and seasonal monsoon rains.
2. Your home town is located at a place which receives the slanting rays of the sun. How is the temperature of your home town different from your boarding school, located at a place that receives the vertical rays of the Sun?
Answer: My home town, being in a region that receives slanting rays of the sun, experiences lower temperatures because the sunlight is spread over a larger area and travels a longer path through the atmosphere. In contrast, my boarding school, located where the sun’s rays are more vertical, receives more concentrated sunlight. This results in higher temperatures, making the boarding school area warmer compared to my home town.
3. Find out the name of the country which has the maximum number of time zones in the world. What is reason behind a country having many time zones and others like India have just one time zone.
Answer: Russia has the maximum number of time zones in the world. This is because Russia spans a vast area from west to east, covering about 11 time zones. A country needs multiple time zones when it extends across a large longitudinal area to ensure that the local time corresponds well with the position of the sun. In contrast, India has a smaller east-west extent and uses a single standard time (IST based on 82°30′E longitude) for the sake of administrative convenience.
4. When you were waiting to welcome New Year in India on December 31, some countries of the world like Australia, New Zealand and Japan have already welcomed New Year. What is the reason for this?
Answer: This happens because of the Earth’s rotation and the time difference between longitudes. Countries like Australia, New Zealand and Japan lie to the east of India. As the Earth rotates from west to east, these countries experience sunrise and the start of a new day earlier than India. Therefore, they celebrate New Year before India does.
Project/Activity
Look at the map of the Time Zones (Fig. 2.7) and answer the following questions:
1. What is the Longitudinal degree of IST __________?
Answer: Do it yourself. Here are the instructions:
- India follows a uniform time called Indian Standard Time (IST).
- IST is based on the longitude that passes through Mirzapur near Prayagraj (Uttar Pradesh).
- If you don’t have the figure, just remember: IST is based on 82°30′E.
- You can confirm this by searching “IST longitude India” online or checking any standard school atlas.
2. If it is 2 a.m. IST what will be the Time at
Tokyo __________, London __________, San Francisco __________?
Answer: Do it yourself. Here are the instructions:
- Step 1: Convert IST to GMT. IST is 5 hours 30 minutes ahead of Greenwich Mean Time (GMT).
2:00 a.m. IST minus 5:30 = 8:30 p.m. GMT (previous day). - Step 2: Use the time difference between GMT and each city:
Tokyo is +9 hours from GMT → 8:30 p.m. + 9 = 5:30 a.m. (next day)
London is GMT 0 → stays at 8:30 p.m. (previous day)
San Francisco is −8 hours from GMT → 8:30 p.m. − 8 = 12:30 p.m. (previous day) - If you don’t have a map or book, you can Google the time difference from GMT for each city.
3. Name the place which is diametrically opposite of India.
Answer: Do it yourself. Here are the instructions:
- India is roughly at 20°N latitude and 77°E longitude.
- To find the opposite side of the globe:
Flip the latitude from north to south → 20°S
Subtract longitude from 180° and switch from E to W: 180° − 77° = 103°W - Search for what lies around 20°S, 103°W — it is in the South Pacific Ocean, near Peru or possibly in the ocean itself.
4. Is the Indian Standard Time ahead of San Francisco Time? Give reasons for your answer.
Answer: Do it yourself. Here are the instructions:
- Yes, IST is ahead of San Francisco time.
- IST = UTC +5:30; San Francisco = UTC −8.
- Total time difference: 5:30 + 8 = 13 hours 30 minutes.
- India lies east of San Francisco, and the Earth rotates from west to east, so time increases as you move east.
- Therefore, when it is daytime in India, it is still the previous night in San Francisco.
Extras
Additional MCQs
1. Which lines are imaginary lines running east to west parallel to the Equator?
A. Lines of latitude
B. Lines of longitude
C. Meridians
D. Great circles
Answer: A. Lines of latitude
38. New Delhi lies at about 30°N latitude; its distance from the Equator is approximately:
A. 3330 km
B. 3000 km
C. 3500 km
D. 3300 km
Answer: A. 3330 km
Additional Assertion/Reason
1. Assertion (A): The intersection of latitudes and longitudes pinpoints a place on the earth’s surface.
Reason (R): These criss-crossing lines of latitude and longitude form a framework known as the Geographic Grid.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (a) Both A and R are true and R is the correct explanation of A.
30. Assertion (A): The geographic grid on a globe functions similarly to a coordinate system on graph paper.
Reason (R): On this grid, lines of latitude represent the x-axis (horizontal) and lines of longitude represent the y-axis (vertical).
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (a) Both A and R are true and R is the correct explanation of A.
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