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
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.
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.
Ron’e Dutta is a journalist, teacher, aspiring novelist, and blogger who manages Online Free Notes. An avid reader of Victorian literature, his favourite book is Wuthering Heights by Emily Brontë. He dreams of travelling the world. You can connect with him on social media. He does personal writing on ronism.
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