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Earth as a Planet: WBBSE Class 9 Geography solutions
Get textual answers, explanations, solutions, notes, extras, MCQs, PDF of Chapter1 Earth as a Planet: WBBSE Class 9 Geography (English medium). However, the educational materials should only be used for reference, and students are encouraged to make necessary changes.
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Summary
For a very long time, people believed the Earth was flat, like a disc or a plate. Different ancient groups had this idea. Some thought it floated on water. The Phoenicians pictured it like half an apple placed in a dish filled with water, showing a flat surface surrounded by water. Early Greeks, Egyptians, and people in the Near East, India, and China also had flat-earth ideas. However, thinkers like Pythagoras suggested the Earth was actually round, like a sphere, about 600 years before the first century A.D. It took many centuries for most people to accept that we live on a sphere.
Several observations helped people understand the Earth is round. The sun rises and sets at different times in different places; if Earth were flat, it would happen everywhere at once. When watching a ship approach from far away, you see its mast or smoke first, then the rest of the hull, which happens because the ship is coming over a curved surface. During an eclipse of the moon, the Earth’s shadow cast on the moon is always circular, and only a round object consistently casts a round shadow. People like Magellan sailed completely around the Earth without falling off any edge, proving it has no edges. Also, the horizon looks like a circle, and this circle gets wider the higher you go. The North Star appears higher in the sky as you travel north, which wouldn’t happen on a flat surface.
Later, photographs taken from space by satellites and astronauts clearly showed the Earth’s spherical shape. Scientists also found that Earth is not a perfect sphere. It is slightly flattened at the North and South Poles and bulges a little at the equator. This shape is called an oblate spheroid. We know this because the distance through the Earth at the equator (equatorial diameter) is about 43 kilometers longer than the distance through the poles (polar diameter). The distance around the equator is also longer than the distance around the poles. An object weighs slightly more at the poles than at the equator because the poles are closer to the Earth’s center. A pendulum clock that keeps correct time in Paris ran slower near the equator because that location is farther from the Earth’s center due to the bulge. The actual, complex shape of the Earth, considering mountains and valleys, is called a geoid, meaning ‘earth-like’.
Earth is the third planet from the Sun and the fifth largest. It is unique because its distance from the Sun allows for moderate temperatures, not too hot or too cold. It has liquid water, an atmosphere with oxygen, and soil, which all support life. Long ago, Eratosthenes calculated the Earth’s circumference quite accurately. Today, we use technology like the Global Positioning System (GPS). GPS uses signals from satellites orbiting Earth to determine the exact location (latitude and longitude) of a receiver anywhere on the planet. It was developed by the U.S. military and helps in navigation, mapping, and many other fields.
Textual Questions, Answers (Oriental)
Multiple Choice Questions
1. Who among the following ancient scholars first gives the idea of round shaped earth?
(a) Homer
(b) Hesiod
(c) Thales
(d) Zimmerman
Answer: (c) Thales
2. The most unique feature of the earth is its—
(a) atmosphere
(b) biosphere
(c) hydrosphere
(d) lithosphere
Answer: (b) biosphere
3. Which of the following is the largest planet in the solar system?
(a) Earth
(b) Mercury
(c) Saturn
(d) Jupiter
Answer: (d) Jupiter
4. Which of the following planets is smaller than the Earth in size?
(a) Jupiter
(b) Mars
(c) Uranus
(d) Neptune
Answer: (b) Mars
5. The circumference of the earth is—
(a) About 40,000 km
(b) About 12,715 km
(c) About 6,400 km
(d) About 250,000 km
Answer: (a) About 40,000 km
6. The equatorial diameter of the earth is—
(a) About 12,714 km
(b) About 6,400 km
(c) About 12,757 km
(d) About 14,532 km
Answer: (c) About 12,757 km
Answer in Very Short
1. What is the exact shape of the earth?
Answer: Earth is not a perfect sphere. It ‘bulges out’ a little at the equator and is flattened at the poles. There are much bigger depressions and bumps on its surface. It is an oblate spheroid.
2. Give a proof of the earth’s equatorial bulge?
Answer: A proof of the Earth’s equatorial bulge is the difference between the length of the Equatorial diameter and Polar diameter. The earth has got an equatorial diameter of 12,757 km through east-west and a polar diameter of 12,714 km through north-south. In length the equatorial diameter is larger than the polar diameter by 43 kms. Hence there is a slight bulging at the equator and a flattening at the two polar regions.
3. What was radius determined by Eratosthenes?
Answer: Based on the calculation using the formula for the circumference of the spherical earth (2πr) and a known circumference length of 24,902 miles, the Earth’s radius was determined to be 3,962 miles.
Answer the Questions Briefly
1. How can you tell that the earth is round?
Answer: Several things show that the shape of the earth is rounded or sphere. The sun does not rise at the same time in every country; if the earth was flat, the sunrise would be everywhere at the same time. When sighting an approaching ship through a telescope, an observer sees first the smoke, then the funnels, and then the hull; if the earth were flat we would see the whole of the ship at one time. The shadow cast by the earth on the moon during the lunar eclipse is circular, and only a round body can cast a circular shadow.
As the earth is spherical in shape, it is possible to circumnavigate the earth; Magellan was the first to go round the earth in a ship without encountering a sharp edge. The Bedford Level Experiment showed that the middle pole B appeared higher owing to the curvature of the earth. The limit of the horizon at a place is circular and the horizon widens as the height of the observer increases. The weight of a substance is nearly the same at all places on the earth, which is possible only when the earth is a sphere. The pole star appears vertically overhead at the North Pole, while its angle of elevation decreases towards the equator, which is possible only when the earth is spherical.
The most clinching evidence is obtained from aerial photographs taken from space by satellites and astronauts, showing the earth’s spherical shape. Also, artificial satellites and space probes are put in orbit on the assumption that the earth is spherical, and the calculations have proved correct.
2. Give three evidences to prove that earth is spherical in shape.
Answer: Three evidences to prove that the earth is spherical in shape are:
(i) Sighting a ship: An observer watching the approach of a ship sees first the smoke, then the funnels, and then the hull. If the earth were flat we would see the whole of the ship at one time.
(ii) The Earth’s shadow: The shadow cast by the earth on the moon during the lunar eclipse is circular. Only a round body can cast a circular shadow.
(iii) Travelling Round the Earth: As the earth is spherical in shape, it is possible to circumnavigate the earth. Magellan was the first to go round the earth in a ship and complete his voyage without encountering a sharp edge.
3. Draw a diagram to show how Eratosthenes calculated the circumference of the earth.
Answer: Eratosthenes, a Greek geographer and astronomer who lived in 3rd century B.C. in Egypt, measured the circumference of the earth. He found that on June 21st, at Syene, the sun’s rays reached the bottom of a deep well at 12 noon, indicating the sun’s rays were vertical. On the same day at Alexandria, the angle of inclination of the Sun at noon was 7°12′ away from the vertical. The distance between Syene and Alexandria was found to be 5000 stadia (1 stadium ≈ 185 metres). The angular difference of 7°12′ is equal to a distance of about 5000 stadia. The circumference of the earth or 360° of angular distance will be equal to 360° ÷ 7°12′ = 50. Hence the length of the circumference of the earth was calculated by Eratosthenes as 5000 × 50 = 2,50,000 stadia or 46,250 km (using 625 stadia = 1 km). This approximate figure is quite close to the actual figure of 40,000 km.
4. Give some proofs about the shape of the earth as an oblate spheroid.
Answer: Some proofs that the Earth has the shape of an oblate spheroid are:
- Difference between the length of the Equatorial diameter and Polar diameter: The earth has got an equatorial diameter of 12,757 km and a polar diameter of 12,714 km. The equatorial diameter is larger than the polar diameter by 43 kms, indicating a slight bulging at the equator and a flattening at the poles, caused by the rotation of the earth.
- Length of circumferences: The length of the equatorial circumference is 40,076 km and the polar circumference is 40,009 km. The equatorial circumference is larger than the polar circumference by 67 km.
- Weight of an Article: The weight of a substance being weighted by a spring balance increases from equator to the pole. This is only possible when the earth has got a shape of an oblate spheroid.
- Pendulum Clock: Jean Richter observed in 1671 that a pendulum clock giving correct time at Paris (49°N) ran slow by two and a half minutes everyday at Cayenne island (5°N, near equator). This is because Cayenne island is more far away from the centre of the earth than Paris due to the equatorial bulge, and the gravitational pull is less, making the pendulum swing slower.
- Length of an Arc: The length of a one-degree arc of latitude is not constant; it changes slightly from the equator to the poles. It is 110.6 km at the equator and 111.7 km at the poles, being 1.1 km longer at the poles, proving the earth is an oblate spheroid.
5. What are the uses of GPS?
Answer: GPS or Global Positioning System is a modern measure to determine the latitude or longitude of a place on the earth. It is a space-based satellite navigation system that provides location and time information in all weather conditions, anywhere on or near the earth with an unobstructed line of sight to four or more GPS satellites. Specific applications include:
(i) GPS is essential for the modern defence system.(ii) It may be used to identify or define the geographical co-ordinates associated with satellite imagery. GPS is used to reduce distortions and to improve the positional accuracy of these images.
(iii) GPS can be used in the ground truthing of satellite images.
(iv) GPS has developed into a cost effective tool for updating GIS or Computer-Aided Design (CAD) systems.
(v) Using GPS to collect data is analogous to digitising a map by moving a mouse or digitising pack over a map.
(vi) GPS is an excellent tool for data collection in many environments where the user can generally see the sky and is able to get close to the objects to be mapped.
Extras
Additional MCQs
1. Which ancient philosopher first postulated that the Earth is spherical?
A. Aristotle
B. Pythagoras
C. Eratosthenes
D. Anaxagoras
Answer: B. Pythagoras
2. In which century did the general acceptance of the Earth’s round shape occur?
A. Sixth century B.C.
B. First century A.D.
C. Middle Ages
D. Nineteenth century
Answer: B. First century A.D.
3. During which period did the flat Earth concept resurge on religious grounds?
A. Renaissance
B. Dark Ages
C. Middle Ages
D. Classical period
Answer: C. Middle Ages
4. Which civilisation believed the Earth was flat until the Gupta period?
A. Greece
B. India
C. China
D. Mesopotamia
Answer: B. India
5. Which civilisation believed the Earth was flat until the seventeenth century?
A. India
B. Egypt
C. China
D. Greece
Answer: C. China
6. Which thinker believed the Earth floated in water like a log?
A. Pythagoras
B. Thales
C. Aristotle
D. Herodotus
Answer: B. Thales
7. Who believed the Earth was a short cylinder with a flat circular top?
A. Anaximander
B. Anaximenes
C. Xenophanes
D. Eratosthenes
Answer: A. Anaximander
8. Which philosopher believed the Earth was flat and rode on air?
A. Anaxagoras
B. Anaximenes
C. Anaximander
D. Hecataeus
Answer: B. Anaximenes
9. Who described the Earth as flat with its lower side extending without limit?
A. Xenophanes
B. Anaxagoras
C. Herodotus
D. Hesiod
Answer: A. Xenophanes
10. Which historian ridiculed the idea of a water-encircled world yet described literal ‘ends’ of the Earth?
A. Hecataeus
B. Herodotus
C. Homer
D. Aristotle
Answer: B. Herodotus
11. Which cosmology held that the Earth is a disc with four continents around Mount Meru?
A. Hinduism and Jainism
B. Jainism and Buddhism
C. Buddhism and Sikhism
D. Hinduism and Buddhism
Answer: B. Jainism and Buddhism
12. Which people featured the world-tree Yggdrasil at the centre of their flat Earth model?
A. Greek
B. Norse
C. Egyptian
D. Chinese
Answer: B. Norse
13. In ancient China, what shape was the Earth believed to be?
A. Circular
B. Square
C. Cylindrical
D. Disc
Answer: B. Square
14. Which observation supports the Earth’s spherical shape by showing that sunrise times vary by location?
A. Different sunrise times
B. Equal shadow lengths
C. Uniform tides
D. Constant daylight
Answer: A. Different sunrise times
15. When observing a ship approaching over the horizon, what is seen first?
A. Smoke
B. Hull
C. Masts
D. Deck
Answer: A. Smoke
16. What shape is the Earth’s shadow on the Moon during a lunar eclipse?
A. Oval
B. Triangular
C. Circular
D. Square
Answer: C. Circular
17. Who was the first to circumnavigate the Earth by ship?
A. Christopher Columbus
B. Vasco da Gama
C. Ferdinand Magellan
D. James Cook
Answer: C. Ferdinand Magellan
18. Which experiment used poles on a canal to demonstrate the Earth’s curvature?
A. Eratosthenes’ experiment
B. Bedford Level Experiment
C. Pendulum experiment
D. Horizon test
Answer: B. Bedford Level Experiment
19. What happens to the visible horizon as the observer’s height increases?
A. Widens
B. Narrows
C. Disappears
D. Remains same
Answer: A. Widens
20. Why does an object weigh slightly more at the poles than at the equator?
A. Greater atmospheric pressure
B. Stronger winds
C. Greater gravity
D. Higher temperature
Answer: C. Greater gravity
21. At which location is the pole star directly overhead?
A. Equator
B. North Pole
C. Tropic of Cancer
D. South Pole
Answer: B. North Pole
22. What type of photographs provide direct proof of the Earth’s spherical shape?
A. Infrared
B. Underwater
C. Aerial
D. Thermal
Answer: C. Aerial
23. What assumption is made about the Earth’s shape when placing artificial satellites in orbit?
A. Flat Earth
B. Spherical Earth
C. Cylindrical Earth
D. Disc Earth
Answer: B. Spherical Earth
24. What term describes a sphere flattened at the poles?
A. Prolate spheroid
B. Geoid
C. Oblate spheroid
D. Ellipse
Answer: C. Oblate spheroid
25. By how many kilometres is the equatorial diameter larger than the polar diameter?
A. 20 km
B. 43 km
C. 67 km
D. 100 km
Answer: B. 43 km
26. What is the equatorial circumference of the Earth?
A. 40,009 km
B. 12,714 km
C. 40,076 km
D. 43,000 km
Answer: C. 40,076 km
27. Which device revealed the Earth’s oblate shape by running slow near the equator?
A. Sextant
B. Pendulum clock
C. Telescope
D. Chronometer
Answer: B. Pendulum clock
28. Who first observed that a pendulum clock ran slow at Cayenne compared to Paris?
A. Isaac Newton
B. Eratosthenes
C. Jean Richter
D. Ferdinand Magellan
Answer: C. Jean Richter
29. At which location did a pendulum clock run slow compared to Paris?
A. Syene
B. Alexandria
C. Cayenne
D. London
Answer: C. Cayenne
30. What is the length of one degree of latitude at the poles?
A. 110.6 km
B. 111.32 km
C. 111.7 km
D. 110.58 km
Answer: C. 111.7 km
31. What name is given to the Earth’s true irregular shape accounting for mountains and valleys?
A. Sphere
B. Ellipsoid
C. Geoid
D. Spheroid
Answer: C. Geoid
32. What is the Earth’s average distance from the Sun?
A. 357,269 km
B. 150 million km
C. 12,757 km
D. 23 hours 56 minutes
Answer: B. 150 million km
33. Which planet is nearest to the Sun?
A. Earth
B. Venus
C. Mercury
D. Mars
Answer: C. Mercury
34. Which planet is closest to Earth?
A. Mars
B. Venus
C. Jupiter
D. Mercury
Answer: B. Venus
35. What is the Earth’s position by distance from the Sun?
A. First
B. Third
C. Fifth
D. Eighth
Answer: B. Third
36. What is the Earth’s position by size among the planets?
A. Third
B. Fifth
C. Seventh
D. Ninth
Answer: B. Fifth
37. What is the Earth’s average surface temperature?
A. 0 °C
B. –18 °C
C. +14 °C
D. +28 °C
Answer: C. +14 °C
38. Which planet is known as Earth’s twin?
A. Mars
B. Mercury
C. Venus
D. Jupiter
Answer: C. Venus
39. How long does it take sunlight to reach Earth?
A. 4.3 minutes
B. 8.2 minutes
C. 12 minutes
D. 1 hour
Answer: B. 8.2 minutes
40. What is the Earth’s age?
A. 3500 million years
B. 4000 million years
C. 4550 million years
D. 4600 million years
Answer: C. 4550 million years
41. What is the Earth’s average radius?
A. 6379 km
B. 6400 km
C. 7000 km
D. 7927 km
Answer: B. 6400 km
42. What is the distance between Earth and the Moon?
A. 150 million km
B. 43,000 km
C. 357,269 km
D. 384,400 km
Answer: C. 357,269 km
43. Approximately how many satellites does Earth have?
A. 1
B. 3
C. 4987
D. 12
Answer: C. 4987
44. Who first calculated the Earth’s circumference around 200 B.C.?
A. Pythagoras
B. Eratosthenes
C. Aristotle
D. Newton
Answer: B. Eratosthenes
45. What formula is used to calculate the Earth’s surface area?
A. πr²
B. 2πr
C. 4πr²
D. πd
Answer: C. 4πr²
46. What is the approximate surface area of Earth?
A. 400 million sq km
B. 500 million sq km
C. 510 million sq km
D. 600 million sq km
Answer: C. 510 million sq km
47. In what year did GPS become fully operational?
A. 1973
B. 1985
C. 1995
D. 2000
Answer: C. 1995
48. How many satellites comprised the original GPS constellation?
A. 12
B. 18
C. 24
D. 30
Answer: C. 24
49. Which department developed GPS?
A. NASA
B. Department of Defence
C. Department of Commerce
D. Department of Transportation
Answer: B. Department of Defence
50. At what altitude do GPS satellites orbit above Earth?
A. 5,000 miles
B. 11,000 miles
C. 22,000 km
D. 36,000 km
Answer: B. 11,000 miles
51. How many orbital paths do GPS satellites travel on?
A. Four
B. Six
C. Eight
D. Twelve
Answer: B. Six
52. What is the minimum number of GPS satellites required to determine a location?
A. Three
B. Four
C. Five
D. Six
Answer: B. Four
53. Who, along with Bradford Parkinson and Roger L. Easton, is credited with creating GPS?
A. Ivan A. Getting
B. Jean Richter
C. Ivan Pavlov
D. Albert Einstein
Answer: A. Ivan A. Getting
54. Which GPS segment includes control stations on Earth?
A. Space segment
B. Ground control segment
C. User segment
D. Processing segment
Answer: B. Ground control segment
55. Which GPS segment includes receivers used by the public?
A. Space segment
B. Ground control segment
C. User segment
D. Master segment
Answer: C. User segment
56. What process is analogous to digitising a map by moving a mouse when using GPS to collect data?
A. Satellite scanning
B. Underwater surveying
C. Field mapping
D. Air surveying
Answer: C. Field mapping
57. What unit did Eratosthenes use to measure the distance between Syene and Alexandria?
A. Miles
B. Kilometres
C. Leagues
D. Stadia
Answer: D. Stadia
58. What is the length of one Egyptian stadia in metres?
A. 150 m
B. 185 m
C. 200 m
D. 300 m
Answer: B. 185 m
59. At which Egyptian city did sunlight reach the bottom of a deep well at noon?
A. Alexandria
B. Thebes
C. Syene
D. Memphis
Answer: C. Syene
60. What angle did Eratosthenes measure at Alexandria to calculate the Earth’s circumference?
A. 5°
B. 7°12′
C. 10°
D. 3°15′
Answer: B. 7°12′
Additional Questions, Answers
1. Who postulated a spherical Earth around 600 B.C.?
Answer: Pythagoras had postulated a spherical Earth 600 years earlier than the first century A.D.
2. In which century A.D. did general acceptance of Earth’s round shape occur?
Answer: The general acceptance of the fact that the Earth is round came about in the first century A.D.
3. What flat-Earth model did ancient Egyptians and Mesopotamians believe?
Answer: The early Egyptians and Mesopotamians thought that the world was portrayed as a flat disk floating in the ocean.
4. What term describes a sphere slightly flattened at the poles?
Answer: A sphere which is slightly flatened at two opposite ends is called an oblate spheroid or oblate ellipsoid. This type of spherical shape is known ‘oblate spheroid’.
5. By how many kilometres does Earth’s equatorial diameter exceed its polar diameter?
Answer: In length the equatorial diameter is larger than the polar diameter by 43 kms.
6. Who first observed Earth’s oblateness using a pendulum clock in 1671?
Answer: The earth is an oblate spheroid or ellipsoid was first observed by Jean Richter, a French astronomer in 1671 using a pendulum clock.
7. Who calculated Earth’s circumference using the tilt of sun-rays at Syene and Alexandria?
Answer: Eratosthenes, who lived in 3rd century B.C. in Egypt, was actually a Greek geographer and astronomer who measured the circumference of the earth using the distance and angle of inclination of the Sun’s rays between Syene and Alexandria.
8. On which date did Eratosthenes note the sun’s rays were vertical at Syene?
Answer: Eratosthenes found that on June 21st, at a place called Syene in Egypt the sun’s rays reached the bottom of a deep well at 12 noon, indicating the sun’s rays were vertical at Syene on that day.
9. What is the average distance between the Earth and the Sun?
Answer: The average distance between the Sun and the Earth is 150 million km.
10. How long does Earth take to complete one rotation on its axis?
Answer: It takes 23 hours 56 minutes and 4 seconds to complete one rotation.
11. What name is given to Earth’s irregular, sea-level-defined shape?
Answer: Scientists have truly given the name ‘geo’ to this form or ‘geoid’ meaning ‘earth like form’ or earth shaped.
12. What does GPS stand for?
Answer: GPS stands for Global Positioning System.
13. Name one of the three original inventors of the GPS system.
Answer: Bradford Parkinson is created with inventing GPS. [Alternatively: Roger L. Easton is created with inventing GPS. Alternatively: Ivan A. Getting is created with inventing GPS.]
14. In which year did GPS become fully operational?
Answer: GPS became fully operational in 1995.
15. What is Earth’s average surface temperature?
Answer: The average surface temperature is +14°C.
16. How many minutes does sunlight take to reach Earth?
Answer: The time taken for the sunlight to come on the earth is 8.2 minutes.
17. What is Earth’s average radius?
Answer: Earth’s Average Radius is 6,400 km (almost).
18. What is observed first when a ship approaches the horizon through a telescope?
Answer: An observer watching through a telescope the approach of a ship sees first the smoke, then the funnels, and then the hull.
19. What circular shadow during a lunar eclipse provides evidence of Earth’s roundness?
Answer: The shadow cast by the earth on the moon during the lunar eclipse is circular. Only a round body can cast a circular shadow, proving the rounded shape of the earth.
20. What did the Bedford Level experiment demonstrate about Earth’s shape?
Answer: The Bedford Level Experiment found that the middle pole B appeared higher owing to the curvature of the earth, which would not happen if the earth were flat.
21. Which direct proof of Earth’s sphericity comes from space-based photographs?
Answer: Aerial Photographs provide the most clinching evidence of the spherial shape of the earth, obtained from photographs taken from space. Pictures taken by satellites show the spherical shape of the earth.
22. What segment of GPS consists of satellites orbiting approximately 11,000 miles above Earth?
Answer: The Space Segment of GPS is a constellation of 24 satellites orbiting 11,000 mile above the earth.
23. Explain two indirect proofs of Earth’s spherical shape.
Answer: Two indirect proofs demonstrating that the shape of the earth is rounded or spherical are:
(i) Sunrise and Sunset: The sun does not rise at the same time in every country. It rises in London, for example, some 5 hours later than in Mumbai. If the earth was flat, the sunrise would be everywhere at the same time. This difference in timing indicates a curved surface.
(ii) Sighting a ship: An observer watching through a telescope the approach of a ship sees first the smoke, then the funnels, and then the hull. If the earth were flat we would see the whole of the ship at one time. This sequential appearance proves the rounded shape of the earth.
24. Describe the methods used by Eratosthenes to measure Earth’s circumference and his calculations.
Answer: Eratosthenes, a Greek geographer and astronomer living in the 3rd century B.C. in Egypt, measured the circumference of the earth. He found that on June 21st, at a place called Syene in Egypt, the sun’s rays reached the bottom of a deep well at 12 noon, indicating that the sun’s rays were vertical at Syene on that day. On the same day at Alexandria in the Nile delta, the angle of inclination of the Sun at noon was 7°12′ away from the vertical.
The distance between Syene and Alexandria was found to be 5000 stadia (Stadiun is an Egyptian unit of measuring distance, equivalent to about 185 metres). Eratosthenes reasoned that the angular difference of 7°12′ corresponded to the physical distance of 5000 stadia. Therefore, the full circumference of the earth (360° of angular distance) would be equal to 360° ÷ 7°12′ = 50 times the distance between the two cities.
Hence, the length of the circumference of the earth was calculated by Eratosthenes as 5000 stadia × 50 = 2,50,000 stadia. This is approximately 46,250 km, which is quite close to the actual figure of 40,000 km.
25. Outline the evidences that verify Earth as an oblate spheroid.
Answer: The evidences that verify the Earth has the shape of an oblate spheroid, meaning it has an equatorial bulge and polar flattening, are:
- Difference between the length of the Equatorial diameter and Polar diameter: The earth has got an equatorial diameter of 12,757 km through east-west and a polar diameter of 12,714 km through north-south. In length the equatorial diameter is larger than the polar diameter by 43 kms. Hence there is a slight bulging at the equator and a flattening at the two polar regions. This is caused by the rotation of the earth.
- Length of circumferences: The length of equatorial circumference is 40,076 km and the polar circumference is 40,009 km. The length of equatorial circumference is larger than the polar circumference by 67 km. Thus the earth has got a shape of an oblate spheroid.
- Weight of an Article: The weight of a substance being weighted by a spring balance increases from equator to the pole. It is only possible when the earth has got a shape of an oblate spheroid. This is because the gravitational pull is stronger at the poles (closer to the centre) than at the equator (further from the centre due to the bulge).
- Pendulum Clock: Jean Richter observed in 1671 that a pendulum clock accurate at Paris (49°N) ran slow by two and a half minutes daily at Cayenne island (5°N, near the equator). He had to shorten the pendulum to correct the time. This is explained by Isaac Newton’s law of gravitation: the distance between the centre of the earth and an object on its surface affects gravitational pull. Due to the equatorial bulge, Cayenne is farther from the Earth’s centre than Paris. The pendulum at Cayenne was attracted less by gravitational force, causing the clock to run slow. This observation supports the oblate spheroid shape.
- Length of an Arc: The length of a one-degree arc of latitude is not constant everywhere on the earth. It changes slightly in length from the equator to the poles. The length of 1° of latitude at the poles is 111.7 km and at the equator it is 110.6 km. It is 1.1 km longer at the poles. If the earth were a perfect sphere, the length of a one-degree arc of latitude would be constant. This variation proves that the earth is an oblate spheroid.
26. What is the concept of geoid?
Answer: Earth is not a perfect sphere, nor is it a simple oblate spheroid. Studies of satellite orbits revealed that the Earth is not a perfect oblate ellipsoid as previously thought. The earth ‘bulges out’ a little at the equator and is flattened at the poles, but there are also much bigger depressions and bumps on its surface, such as areas of low atmospheric pressure causing climatic changes. Because the Earth is unique, its shape is also unique. Scientists have truly given the name ‘geo’ to this form or ‘geoid’, meaning ‘earth like form’ or earth shaped. Mountains like the Himalayas or deep valleys are also just a dot when considering the size of the earth in this context.
27. Discuss Earth’s unique position in the solar system and how it supports life.
Answer: The earth is the third planet in line from the Sun and the fifth largest in the solar system. Though relatively small, the earth is a unique member of the solar system. Its unique position and characteristics make it the only known planet which has life on it.
Because of its distance from the Sun (average 150 million km), its rotation, and the atmosphere, its temperatures are moderate. The earth is neither too close nor too far from the Sun. Had it been a little nearer it would have been too hot for life, and if further away it would have been too cold; the seas and rivers would have remained frozen throughout. The average surface temperature is +14°C.
Several factors resulting from its position and nature make life possible on Earth:
- Distance from the Sun: Ensures moderate temperatures, neither too hot nor too cold.
- Presence of Water: Three-fourths of earth’s surface is covered with water, necessary to sustain all types of life. Life began in the earth’s oceans 3000 million years ago.
- Water cycle: The air and water, with the action of sunlight, set the water cycle in motion, making water continuously available to living things. This does not happen on any other planet.
- Presence of large quantities of oxygen: There is presence of large quantities of oxygen in the uncombined state, which is necessary to support all forms of life.
- The presence of the atmosphere: The atmosphere prevents all the heat from the Sun from reaching the earth during the day, keeping temperature relatively cool. At night, it acts like a blanket, preventing heat from escaping and keeping the temperature warm. It also contains nitrogen and oxygen which helps to develop life.
- Soil: The earth is a ball of rocks. The actions of sunshine, air and water provide a valuable soil layer that supports all life on earth.
These factors combine to make Earth a unique planet, the home of mankind, shared with about one million different kinds of animals and more than 350,000 types of plants.
28. Describe the functions of the three segments of the GPS system.
Answer: GPS has three systems of functions, known as segments:
(A) Space Segment: The GPS is a constellation of 24 satellites orbiting 11,000 miles above the earth, travelling on six separate paths. These satellites transmit signals.
(B) Ground Control Segment: This segment involves monitoring stations, a master control station, and control sections on the ground. The receiver (part of the User Segment, but interacts with Ground Control data) requires the satellite signal, obtains the Almanac and Ephemeris data (orbital information) from the satellites, which is managed and uploaded by the Ground Control Segment.
(C) User Segment: The receiver performs the math to calculate its position based on signals received from multiple satellites. The position is determined based on triangulation. The final stage can involve transferring collected GPS-based data from a field device to a target database, such as for Geographic Information System (GIS).
29. Examine three applications of GPS in modern geographic information systems and defence.
Answer: Three applications of GPS are:
(i) GPS is essential for the modern defence system.
(ii) GPS may be used to identify or define the geographical co-ordinates associated with satellite imagery. It is also used to reduce distortions and to improve the positional accuracy of these images.
(iii) GPS can be used in the ground truthing of satellite images and is a cost-effective tool for updating GIS or Computer-Aided Design (CAD) systems. Using GPS to collect data is analogous to digitising a map by moving a mouse or digitising pack over a map, where users move along the surface of the earth to record geographic co-ordinates.
30. Explain the importance of measuring arcs of latitude and longitude in determining Earth’s shape.
Answer: Measuring the length of arcs of latitude is important in determining Earth’s shape because it provides evidence that the Earth is an oblate spheroid, not a perfect sphere. If the earth were a perfect sphere, the length of a one-degree arc of meridian (latitude) would be a constant value everywhere. However, measurements show that the length of a degree of latitude is not constant; it changes slightly in length from the equator to the poles. Specifically, the length of 1° of latitude at the poles is 111.7 km, while at the equator it is 110.6 km. This difference, being 1.1 km longer at the poles, proves that the Earth is flattened at the poles and bulges at the equator, consistent with the shape of an oblate spheroid. The length of 1° of longitude also varies, being largest at the equator (111.32 km) and decreasing towards the poles, but the variation in the length of a degree of latitude is key evidence for oblateness.
31. Discuss how Earth’s atmosphere and water cycle contribute to making the planet habitable.
Answer: Earth’s atmosphere and water cycle are crucial factors that contribute to making the planet habitable:
The presence of the atmosphere: The atmosphere surrounding the earth plays a vital role in regulating temperature. (i) It prevents all the heat from the Sun from reaching the earth during the day, keeping the temperature relatively cool. (ii) At night, it acts like a blanket by preventing all the heat from escaping, thus keeping the temperature warm at night. The atmosphere also contains nitrogen and oxygen, which are essential gases that help to develop and sustain life.
Water cycle: The interaction of air and water with the action of sunlight sets the water cycle in motion. This cycle ensures that water is continuously available to living things across the planet. The continuous availability of water, driven by the water cycle, is necessary to sustain all types of life. This process does not happen on any other planet in the same way, highlighting its importance for Earth’s habitability.
