WBBSE Solutions for Class 9 Geography and Environment Chapter 1 Earth As A Planet

Chapter 1 Earth As A Planet Short Questions With Answers:

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Question 1. What is the age of the earth according to a majority of opinion?
Answer. About 4-5 billion years.

Question 2. At what rate moon is moving away from the earth?
Answer. 13 cm per year.

Question 3. What is the distance between the earth and the moon?
Answer. 384400 km.

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Question4. What do you mean by centrifugal force?
Answer. A force that pulls the mass away from the centre of a rotating body.

Question 5. Give the formula for calculating the age of the oceans on the basis of their salinity. n Total oceanic salt
Ans.

\( \text { Age of the oceans } \)=\( \frac{\text { Total oceanic salt }}{\text { Annual rate of oceanic salinity }} \)

Question 6. Define star.
Answer. The celestial body which has its own light and heat is termed a star.

Class 9 Geography Solution WBBSE

Question 7. What are referred to as planets?
Answer. The celestial body which does not have its own light and heat but is illuminated by the light of the star is known as a planet.

Question 8. What do you mean by Satellite?
Answer. The celestial body which revolves around its planet is given the name of the satellite.

Question 9. What do you mean by solar system?
Answer. The solar system is the sun family consisting of the sun, the 8 planets, and dwarf planets satellites along with meteors and asteroids.

Question 10. What is the universe?
Answer. Thousands of galaxies form the universe.

Question 11. What is the mean distance between the sun and the Earth?
Answer. 14,95,98,000 km. [In terms of light year it is 8.311 minutes per year].

Question 12. What is the age of the earth?
Answer. Age of the Earth: It is generally believed that the Earth is four to five billion years old.

Question 13. What is the position of the Earth according to the distance from the Sun?
Answer. Third.

Question 14. What percentage of Earth’s surface is covered with water?
Answer. 70.9%

Question 15. Name the nearest planet to the Sun.
Answer: Mercury.

Question 16. Name the closest planet to the Earth.
Answer: Venus.

Question 17. State the position of the Earth in terms of the size of the planets.
Answer: Fifth.

Question 18. Name the brightest planet in the solar system.
Answer: Venus.

Question 19. Which planet is called Morning Star or Evening Star?
Answer: Venus.

Question 20. What is the weight of the Earth?
Answer: 6000 billion tonnes.

Question 21. What is the exact diameter of the Earth at the Equator?
Answer: 12757 km.

Question 22. What is the exact diameter of the Earth at the Poles?
Answer: 12714 km.

Question 23. What is the average radius of the Earth?
Answer: 6400 km (approx.)

Question 24. What is the circumference of the Earth around the Equator?
Answer: 40076 km.

Question 25. What is the circumference of the Earth around the Poles?
Answer: 40,000 km.

Question 26. What is the difference between Equatorial diameter and Polar diameter?
Answer: 43 km.

Question 27. What is the average distance between Earth and the sun?
Answer: 150 million km.

Question 28. Who calculated the circumference of the Earth earliest?
Answer: Eratosthenes. (200 B.C.)

Question 29. What is the circumference of the Earth according to Eratosthenes?
Answer: 43,000 km.

Question 30. What is the total surface area of Earth?
Answer: 510 million sq. km.

Class 9 Geography Solution WBBSE

Question 31. What is the time taken by the Sunlight to reach the Earth?
Answer: 8.2 minutes.

Question 32. Name the satellite of the Earth.
Answer: Moon.

Question 33. Name the biggest planet in the solar system.
Answer: Jupiter.

Question 34. How many times the Sun is bigger than the Earth?
Answer: 13 lakh times.

Question 35. What is the mass of the Earth?
Answer: 6.5 x 10²⁷ tonnes.

Question 36. Who first declared that the Earth is round?
Answer: Aristotle.

Question 37. What is the age of the earth according to majority opinion?
Answer: About 4-5 billion years.

Question 38. At what rate moon is moving away from the earth?
Answer: 13 cm per year.

Question 39. What is the age of the oceans according to John Joly?
Answer: 80 million years.

Question 40. Name two minerals which contain the maximum amount of radioactive elements.
Answer: Uranium and Thorium.

Question 41. What is angular velocity?
Answer: Angular velocity is the angle moved by a rotating body per unit of time at a point on the axis of rotation.

Question 42. Define angular momentum.
Answer: Angular momentum is the product of mass, angular velocity and square of the radius of the rotating body.

Question 43. What is meant by proto-sun?
Answer: Our original sun has been given the name of proto-sun by Chamberlin and Moulton.

Question 44. What must be the location of the stars moving across the sky in a circle directly overhead?
Answer: The location must be at the North or South Pole.

Question 45. Who is a selenographer?
Answer: A selenographer studies the geography of the moon.

Chapter 1 Earth As A Planet True Or False Type

Question 1. The moon has no clouds.
Answer: True

Question 2. The moon has gravitational attraction.
Answer: True

Question 3. The Radius of the earth was first measured by Eratosthenes.
Answer: True

Question 4. Mercury is the farthest planet.
Answer: False

Question 5. The polar diameter of the earth is 12,714 Km.
Answer: True

Question 6. Jupiter has a ring around it.
Answer: False

Question 7. The moon has no rotation.
Answer: True

Question 8. Jupiter is an outer planet.
Answer: True

Class 9 Geography Solution WBBSE

Question 9. Pluto is the farthest dwarf planet.
Answer: True

Question 10. Uranus has a ring around it.
Answer: False

Question 11. Jupiter is the most beautiful planet. 
Answer: False

Question 12. Mercury has the shortest length of the year.
Answer: True

Question 13. The earth is the fifth largest planet in the Solar System.
Answer: True

Question 14. The average radius of the earth is 6000 kilometres.
Answer: False

Question 15. The average distance of the earth from the sun is about 150 million km.
Answer: True

Question 16. The earth is of an oblate spheroid.
Answer: True

Question 17. The difference between the equatorial diameter and the polar diameter is 60 km.
Answer: False

Question 18. Venus is also known as the “Earth twin”
Answer: True

Question 19. For practical purposes, Earth is considered to be spherical
Answer: True

Question 20. Mercury is the hottest planet
Answer: Flash

Question 21. Geoid means” flattened at the poles”.
Answer: False

Chapter 1 Earth As A Planet Fill In The Blanks

Question 1. Distance between the earth and the moon is______.
Answer: 384400 km.

Question 2. Mercury takes days to move around the sun______.
Answer: 88 days.

Question 3. The smallest planet is_______.
Answer: Mercury.

Question 4. The speed of light is miles per second_______.
Answer: i86,ooo

Question 5. is the largest planet______.
Answer: Jupiter.

Question6. The exact shape of the earth is called_______.
Answer: Geoid.

Question 7. The equatorial diameter of the earth is______.
Answer: 12,757 km.

Question 8. The earth is a_________.
Answer: Geoid.

Question 9. The polar diameter of the earth is______.
Answer: 12714 km.

Class 9 Geography Solution WBBSE

Question 10. The equatorial circumference of the earth is______.
Answer: 40076 km.

Question 11. The sun is times larger than the earth_____.
Answer: 13 lakhs times.

Question 12. Mercury is a planet_______.
Answer: Inner.

Chapter 1 Earth As A Planet 2 Marks Questions And Answer

Question 1. Why Earth is called ‘Blue Planet’?
Answer: The Earth is called a blue planet because of the colours of the seas and oceans. From space, the earth is seen as blue and that is why it is called Blue Planet.

Question 2. What do you mean by the term “The Earth as a Planet”?
Answer:

The Earth as a Planet

The earth, as a planet, is a member of our social family amongst the 8 planets, it is one of them. As a planet, it has life on it.

Question 3. What is the Milky Way?
Answer:

Milky way

The galaxy of which our sun is a member appears in the sky as the Milky Way. The Milky Way is only a small part of our Galaxy.

Question 4. What is the length of the elliptical path of the Earth?
Answer:

Length of the elliptical path of the Earth

96 crore km.

Question5. What is the difference between a planet and a satellite?
Answer:

The difference between a planet and a satellite

A planet is a heavenly body which revolves around the sun in its fixed orbit but a satellite is a body which revolves around the planet.

Question6. What is Sun’s Ecliptic?
Answer:

Sun’s Ecliptic

Due to the Earth’s revolution the apparent annual movement of the sun’s rays varies between 23(½)° North & 23(½)° South is called the Sun’s Ecliptic.

Question7. State the status of Pluto in the solar system. 
Answer:

Status of Pluto in the solar system

Pluto is nowadays not considered a planet of the solar system. It has been given a special status of a ‘dwarf planet’.

Question 8. Why weight in polar regions are more compared to equatorial regions?
Answer: Compared to equatorial regions, polar regions are nearer to the earth’s centre. So, the gravitational pull is more. The weight of any object taken in the equatorial region, the same object will weigh more in the polar region because of the greater gravitational pull.

Question 9. What does Thales & Anaximander believe regarding the shape of the Earth?
Answer: Thales (550 BC) thought the earth floated in the water like a log. It has been argued, however, that Thales actually believe in a round earth. Anaximander (550 BC) believed that the earth was a short cylinder with a flat, circular top that remained stable because it was the same distance from all things.

Question 10. Discuss how seeing from a ship proves that the Earth is round.
Answer: An observer watching through a telescope the approach of a ship seas 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 proves the rounded shape of the earth.

Question 11. What does the word Geoid mean?
Answer:

Geoid

The word ‘geoid’ means ‘earth-like form’ or ‘Earth – Shaped’.Scientists have given this name to +he shape of the Earth.

Question 12. What is the rob of Earth’s atmosphere?
Answer:

Rob of Earth’s atmosphere

(1) Atmosphere around the earth prevents all heat from the Sun from reaching the earth during the day, keeping temperatures relatively cool.

(2) At night it acts like a blanket by preventing all the heat from escaping, thus keeping the temperature warm at night.

Question 13. Measure the area of the earth. no 291601

Answer:. Measurement of area of the earth:

Formula for measuring the area of the earth is 4πr²

∴[ Here π = 3.142857, r = 6,379 km or 3,962 miles]
∴4 x 3.142857 x (6,379)2 1369 = 4 x 3.142857 x 40691641 = 511,552,035 sq. km.

Geography Class 9 West Bengal Board

Question 14. Discuss in brief Earth’s unique position in the solar system.
Answer:

Earth’s unique position in the solar system

Earth is in the third position from the Sun and is the largest terrestrial planet. It is the fifth largest planet in terms of size and mass but is the dense planet (5,513 Kg/m3) among all the planets.

Earth is so positioned in the Solar System that it remains protected from asteroids and meteoroids. It is special and unique in one sense that it is the only planet known to foster life in the whole Solar System.

Question15. What do you mean by Terrestrial Planet?
Answer:

Terrestrial Planet:

A terrestrial planet is a planet that is composed primarily of silicate rocks or metals,

Example: Mercury, Venus, Earth and Mars.

Question16. Which planet is known as Earth Twin & why?
Answer: Venus is the only planet in the solar system to spin in the opposite direction of its orbit. It is like Earth in size and mass and hence also known as the “Earth twin”.

Question17. What was the defect in the calculation of the circumference of the Earth by Eratosthenes?
Answer:

Two defects in the method of Calculation:

Eratosthenes was not fully right although his method of calculation of the circumference of the earth was quite good and educative. Eratosthenes measured the distance in Stades, his result for. the circumference being 2,52,000 States.

He could not calculate it accurately at first because Alexandria lies well to the west of the meridian through Syene, while Syene itself is several kilometres north of the tropic of cancer where the sun shines vertically on June 21.

Question18. State two uses of GPS.
Answer:

Uses of GPS

(1) GPS is essential for the modern defence system.
(2) It may be used to identify or define the geographical coordinates associated with satellite imagery.

Question19. Why is Venus a brighter object in the sky than Mars?
Answer: Venus is closer to the sun than Mars and hence receives more sunlight to reflect. It is larger than Mars, so the reflecting surface is greater in area. Venus is a better reflector of sunlight than the cloudless Martian surface. As a result of all these factors, Venus is the brightest object in the sky after the sun and the moon.

Question 20. Why is the average temperature on Mars lower than that on earth? Why is there a great variation in Martian temperatures?
Answer: Being \(1 \frac{1}{2}\) time farther from the sun than the earth, Mars receives considerably less solar energy per metre square than we do. Mars has an extremely thin atmosphere. So little of the heat is retained by the atmospheric blanket of Mars after nightfall. Daytime temperatures at the equator on Mars rise to 20°C but at night drop to – 70°C.

Question 21. Explain why the moon has only one day in a year.
Answer: The moon turns, i.e., rotates only once during one revolution around the earth that is the time of the moon’s rotation and revolution is the same (27— days). That is why the moon has only one ‘day’ in a ‘year’. 1 day for the moon means almost 2 weeks of sunshine (daytime) and 2 weeks of darkness (nighttime). With each new moon, the moon begins its day as well as a new year. So, 1 moon year = time interval between two new moons.

Geography Class 9 West Bengal Board

Question22. Why do not lunar eclipses occur every fortnight?
Answer: An eclipse occurs when the sun, the earth, and the moon become collinear i.e., they are in a straight line in the plane of the ecliptic. However, a lunar, eclipse does not occur on every full moon, because the moon’s orbit is inclined at an angle of 5°9′ to the earth’s orbital plane of the escape entering into the umbra. Thus of the occurrence of an ecliptic, it will be a lunar eclipse, the moon must be very close to the plane of the ecliptic on a full moon day.

Question23. Compare the size of the moon with that of the sun and the earth.
Answer: The diameter of the earth is\(\frac{1}{100}\)  that of the sun. The diameter of the moon is\( \frac{1}{401}\) that of the sun. The sun’s diameter is 1,392.00 km. It would take 49 spheres like the moon to fill the volume occupied by the earth. The moon’s surface is not very large i.e. 36 million sq km even smaller than two America.

Question24. Why is the sky blue? How does the sky appear to an astronaut the earth’s atmosphere during the day, and during the night?
Answer: The blue colour of the sky is due to the scattering of the sun’s light by molecules and dust particles in the atmosphere. Blue light is scattered more effectively than red; hence the sky, which we see only by scattered light, has an excess of blue. Above the atmosphere, the sky appears black, and the stars are visible to astronauts all the time.

Question25. Why do you think stars twinkle when seen from the ground but not when seen by astronauts in space vehicles?
Answer: Irregularities in the atmosphere cause the light from a star to be randomly deviated to some extent by refraction. These deviations are perceived as twinklings; they are not apparent to an observer of the atmosphere.

Question26. How is it possible to distinguish the planets from the stars
(1) By observations with the naked eye?
(2) By observations with a telescope?
Answer:
(1) When viewed over a period of time a planet will be seen to change its position in the sky relative to the stars.
(2)Seen through a telescope, the planets appear as disks whereas the stars, which are much farther away, appear as point of light.

Question27. List the planets in order of their size.
Answer:

(1) Jupiter
(2) Saturn
(3) Neptune
(4) Uranus
(5) Earth
(6) Venus
(7) Mars
(8) Mercury.

Question28. List the planets in order of their increasing distance from the sun.
Answer:

(1) Mercury
(2) Venus
(3) Earth
(4) Mars
(5) Jupiter
(6) Saturn
(7) Uranus
(8) Neptune and
(9) Pluto
(10) Vulcan.(the last two are dwarf planets).

Question29. What is Syzygy?
Answer:

Syzygy

Syzygy means three bodies in a line. This occurs at the time of the new moon or full moon when the sun and the moon are lined up with the earth.

Question30. When was the first artificial earth satellite launched into space successfully? What was the name of the satellite?
Answer: October 4, 1957, Sputnik 1.

Chapter 1 Earth As A Planet 2 Marks Questions And Answers (Short Notes)

Question l. The Solar System.
Answer:

Solar System

The night sky seen from all parts of the earth reveals a number of twinkling stars, the milky way, other star-like bodies called planets and different phases of the moon on different days. The earth, all the major eight planets 32 satellites and some 1700 minor planets or asteroids are members of the sun’s family or the solar system.

Geography Class 9 West Bengal Board

Question 2. Asteroids.
Answer:

Asteroids

It is commonly believed that they are fragments of some planet which had its orbit between those of Mars and Jupiter and which disintegrated for reasons which are not yet found. The first asteroid was observed by Guiseppe Piazzi in 1801.

Question 3. View of the earth from space.
Answer:

View of the earth from space

The photography of the earth taken from space shows the earth’s spherical body. As viewed from space, the earth appears like a large globe covered with clouds. Through the gaps in the cloud, the earth’s surface is seen: the polar ice-caps appear brilliant white, the deserts yellowish or red, the forested part dark blue or blue-green, grasslands or cultivated regions generally dull yellow and the oceans appear dark blue except the brilliant patches of reflection of sunlight.

Nearly one-third of the earth’s surface is covered by ocean water and it looks blue. For its blue appearance in space, the earth is called “a Blue Planet”.

Question 4. GPS?
Answer:

GPS

GPS or Global Positioning System is a modern measure to determine the latitude or longitude of a place on the earth. The system is functioned by artificial satellites. The Global positioning system is a space-based satellite navigation system that provides location and time information in all weather conditions, anywhere on or near the earth where there is an unobstructed line of sight to four or more GPS satellites.

Chapter 1 Earth As A Plane 3 Marks Questions And Answers

Question l. Why earth is called GEOID?
Answer:

A term sometimes used to signify the shape of the Earth; the later is often taken to be oblate spheroid, but in view of certain variations, the term GEOID, which simply means earth-shaped body, has been introduced.

The surface of the earth is not smooth and even, but broken up by high mountains and deep seas. It is said that the highest point of the earth’s surface stands at 8,898m. above sea level and the lowest point is at 11,033m below sea level. So the earth’s shape can not be accurately described through any geometrical figure. So the earth is referred to as a GEOID. [It is always written in capital letters]

Question 2. Give a description of the size of the earth & its comparison with different other planets with respect to size.
Answer. Our Earth is in the third position from the Sun among the eight planets that orbit the Sun. It is the fifth largest planet in respect of its size or relative bigness when compared to other planets. The size of a planet is determined by its diameter. If we consider the chart given below we can compare the relative size of our Earth with the other planets :
Table showing diameters of the planets of the Solar System

 

 

Earth is the fifth largest in size after the giant planets Jupiter, Saturn, Uranus and Neptune.

If we take the size of Earth as 1, then Jupiter is about 11.209 times bigger than our Earth having a diameter of 1,42,800 Km as compared to 12,757 Km of our Earth. Saturn, Uranus and Neptune follow Jupiter in order of size but all three are bigger than the earth by 9.44, 4.007 and 3.883 times respectively. The diameter of Saturn is 1,20,000 Km, that of Uranus is 51,118 Km and Neptune is 49,528 Km.

Among the smaller planets close to the Sun, called terrestrial planets, our Earth is the largest. The other planets are Mercury, Venus and Mars. The planet Venus is sometimes called the Earth’s twin as it closely follows the Earth in size.

Geography Class 9 West Bengal Board

Our Earth is about 1/0.949 times bigger than Venus whose diameter is 12,014Km. Mars is slightly more than half the size of the Earth. It has a diameter of 6,787 Km. Mercury, the smallest among all the planets of the solar system has a
diameter of 4,578 Km. The Earth is about 1/0.382 times bigger than Mercury.

Question 3. Given an account of the Bedford-level experiment.
Answer.

Bedford level experiment:

An experiment carried out by Dr Wallace in Bedford canal, Norfolk, England during the nineteenth century gave us convincing proof of the Earth’s curvature. A set of three identical poles of equal heights were fixed a mile apart above the water level along a straight stretch of this canal.

When observed carefully through a telescope it was noticed that the middle pole was about 8 inches higher than the other two poles when observed from either end because of the curvature of the Earth.

 

Question 4. Discuss how the position of the North Star shows the shape of the Earth.
Answer.

Position of the North Star :
Different stars appear to change or shift their position in the sky with the change in the observer’s position on the Earth’s surface. An observer at the North Pole (90° N) always finds the North Star (Pole star) vertically overhead. As he proceeds southwards, say at 45° North latitude, he finds the North Star midway between the zenith and the horizon. If he moves further south towards the equator (0°), he would observe the North Star at the horizon. The North Star, therefore, appears to shift its position following the arc of a circle.

Question 5. Discuss what aerial photos & artificial satellites reveal regarding the shape of the Earth.
Answer.

Aerial Photographs :

The most clinching evidence of the spherical shape of the earth is obtained from photographs taken from space. Pictures taken by satellites show the spherical shape of the earth. The astronauts from the moon have taken pictures of the earth showing its spherical shape.

Artificial Satellites :

Artificial Satellites and many space probes are put in orbit on the assumption that the earth is spherical. The calculations have proved correct and the space probes of other planets of the solar system have provided valuable data.

Question 6. Determine the diameter & radius of the earth.
Answer.

Determine of diameter and Radius of the earth :

We know the formula of the circumference of the spherical earth is 2πr.

Here π=\(\frac{22}{7}\)  3.142857;
r = radius of the earth.
We know the length of the earth’s circumference = 24,902 miles.

∴2πR = 2 x 3 142857 x r.
∴2 x 3 142857 x r = 24, 902 mile (equation)

r= \(\frac{24,902}{2 \times 3 \cdot 142857}\)

r = 3,961.68 miles

∴ Earth’s radius = 3-962 mile.
∴ Diameter of the earth = 3-962 x 2 = 7,924 mile or 12,758 km.

Question7. What is the importance of the spherical shape of the Earth?
Answer.

Importance of the spherical shape of the Earth

(1) We calculate time by a system based on the earth as a sphere.
(2)We determine the location of a place on the earth by means of a grid based on the shape of the globe.
(3)Our sense of direction is also based on the earth’s spherical shape.
(4) Differences in temperature from place to place and currents in the oceans and atmosphere are related to the earth’s sphericity.

Class 9 WBBSE Geography Question Answer

Question 8. Explain the concept of the geoid.
Answer.

The concept of the geoid

We learned that the Earth is not a perfect sphere but an oblate spheroid or an oblate ellipsoid. Recent observations and close examination of the Earth’s surface show certain unexplained anomalies. The shape of an oblate spheroid has variations. Therefore the Earth has an undulating or irregular surface.

This irregular surface does not resemble the geometric ellipsoid shape or any known shape. It is absolutely Earth’s own shape and matches with the term Geoid, meaning ‘Earth-shaped’. The geoid is the shape that the surface of the ocean would take under the influence of Earth’s gravitation and rotation alone.

The surface is extended through the continents. All points on the geoid have the same gravitational potential and the force of gravity acts everywhere perpen- DiCarlo the geoid. This means that the plumb line always points perpendicular and the water level is parallel to the geoid.

So, a geoid is the equipotential surface of the Earth’s gravity field. The gravitational field of the Earth is neither perfect nor uniform. The strength of gravity would not be the same everywhere^ because density and mass vary all through the Earth.

This is due to magma distributions, mountain ranges (Mount Everest 8,848 m), deep sea trenches (Mariana trench 10,924 m below sea level) and so on. So, it is important to note that geoid depends on gravitational measurements and not on Earth’s surface (topographic features).

Thus the geoid is defined as an imaginary surface that coincides with the mean sea level in the ocean and its extension through the continents. It is also defined as the surface of the Earth’s gravity field.

The shape so formed is not a flattened sphere but slightly like a pear. This shape is determined by the combination of survey techniques and mathematical analysis known as geodesy.

Question 9. What is a solar eclipse? What are the ‘nodes of the moon’? What are Rahu and Ketu ?
Answer.

Solar eclipse:

As the moon goes around the earth, once each month, it usually passes above or below the sun. We do not see it in the bright daytime sky, but on occasions when the moon passes directly between the sun and the earth, it hides the sun. This is called an eclipse of the sun or solar eclipse.

To hide the sun, the orbiting moon has to cut the ecliptic at two points which are called the moon’s nodes. Rahu and Ketu are the Indian names for these nodes of the moon. Rahu is the ascending node and Ketu is the descending node.

Class 9 WBBSE Geography Question Answer Chapter 1 Earth As A Planet 5 Marks Questions And Answers

Question l. How is the earth called a living planet?
Answer.

Earth – A Living Planet :

In the endless expanse of the universe, the earth is like an insignificant tiny speck. Despite its insignificant size, it is a unique planet not only in the Solar System, but also in the whole universe. Life exists only on it. Animals, plants, micro-organisms and numerous other living beings live on it. The following factors have made life possible on our earth.

(1) The distance of the earth from the sun :
Mercury and Venus are very close to the sun. Therefore, they are very hot, even lead can melt there. On the other hand, there are other planets which are too far from the sun. Hence, they are very cold and even liquids and gases are in a frozen state there. But our earth is at an optimum distance from the sun. So, the earth has an average temperature of 15°C. The range of temperature varies so much that water is found in solid, liquid and gaseous states on our earth. Water is a prerequisite for all forms of life. Life originated and developed in the water then it spread to land. Therefore, plants grow and animals live here.

(2)The existence of three realms on the earth :
The earth is the only known planet in the universe where the atmosphere, hydrosphere and lithosphere exist. Mercury, Venus and Mars have lithosphere and atmosphere; they do not have hydrosphere. Jupiter and Saturn are gaseous planets, which do not have either a lithosphere or hydrosphere. Hence, there is no life on these planets.

(3)The right mixture of gases in the Earth’s atmosphere :
Earth’s atmosphere has an ideal mixture of nitrogen, oxygen-carbon dioxide and ozone. Non-availability of oxygen to our body, even for a fraction of a second, makes us restless. The atmospheres of Venus and Mars mainly consist of carbon-di-oxide. Hydrogen and helium, dominate the atmosphere of Jupiter.

(4)The presence of the ozone layer in the atmosphere of the earth :
The ozone layer absorbs a large proportion of the sun’s ultraviolet radiation. Without this absorption, the earth would be subjected to a degree of ultraviolet radiation which is injurious to plants and animals.

Class 9 WBBSE Geography Question Answer

(5)The ideal duration of day and night :
The average duration of day and night on the earth is of 12 hours each. A single night on Mercury is as long as 30 earth nights. On Venus, the night is still longer. It is about 122 earth nights long. In contrast on Jupiter and Saturn, the duration of a night is only five hours each.

Question 2. What are the uses of GPS?
Answer.

Uses of GPS

GPS or Global Positioning System is a modern measure to determine the latitude or longitude of a place on the earth. The system is functioned by artificial satellites.

The Global positioning system is a space-based satellite navigation system that provides location and time information in all weather conditions, anywhere on or near the earth where there is an unobstructed line of sight to four or more GPS satellites.

The Origin of GPS :

The GPS project was developed in 1973 to overcome the limitations of the previous navigation system, integrating ideas from several predecessors, including a number of classified engineering design studies from the 1960s.

GPS was created and realized by the U.S. Department of Defence (D.D.) and was originally run with 24 satellites. It became fully operational in 1995. Bradford Parkinson, Roger L. Easton, and Ivan A. Getting are credited with inventing it.

How it functions :

GPS has three systems of functions :

(1) Space Segment: The GPS is a constellation of 24 satellites orbiting 11,000 miles above the earth, travelling on six separate paths.

(2)Ground Control Segment: The receiver requires the satellite signal, obtains the almanack and ephemeris data from the satellites and performs the math to calculate its position. The position is determined based on triangulation.

(3)User Segment: The final stage of the process of GPS-based data collection for GIS is to transfer the data from the field device to the target database.

Application of GPS :

(1) GPS is essential for the modern defence system,
(2) It may be used to identify or define the geographical coordinates associated with satellite imagery. GPS is used is reduce distortions and to improve the positional accuracy of these images,
(3) GPS can be used in the ground frothing of satellite images,
(4) GPS has developed into a cost-effective tool for updating GIS or computer-aided design (CAD) systems,
(5) Using GPS to collect data is analogous to digitising a map by mousing a mouse or digitising a pack over a map. The users of GPS equipment simply move along the surface of the earth and the geographic coordinates,
(6) However, 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.

Question 3. Give some proof about the shape of the earth as an oblate spheroid.
Answer.

The following study proves the shape of the earth as an oblate spheroid :

(1)Difference between the length of the Equatorial diameter and Polar diameter :

(1) The earth has got an equatorial diameter of 12,757 km through the east-west and a polar diameter of 12,714 km through the north-south. In length, the equatorial diameter is larger than the polar diameter by 43 km. 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.

(2)Length of circumferences:
The length of the equatorial circumference is 40,076 km and the polar circumference is 40,009 km. The length of the equatorial circumference is larger than the polar circumference by 67 km. Thus the earth has got a shape of an oblate spheroid.

(3)Weight of an Article :
The weight of a substance is related to the effect of the force of gravity on that substance. The weight of a substance being weighted by a spring balance increases from the equator to the pole. It is only possible when the earth has got a shape of an oblate spheroid.

Class 9 WBBSE Geography Question Answer

(4)Pendulum Clock :

The earth is an oblate spheroid or ellipsoid and was first observed by Jean Richter, a French astronomer in 1971. He observed that a pendulum clock which gave the correct time at Paris (49°N) ran slowly by two and a half minutes every day at Cayenne island (5°N) in French Guiana (South America). With a view of getting the correct time at Cayenne island, he had to cut short the pendulum by a quarter of an inch.

Fifteen Years later of this observation, Sir Isaac Newton discovered the laws of gravitation. It is mentioned in the laws that the more the distance between the centre of the earth and the object on the earth’s surface, the less gravitational pull would act upon the object. Due to the equatorial bulge and polar flattering, Cayenne island (near the equator) is far away from the centre of the earth than Paris (which lies nearer the pole). As the pendulum at Cayenne was attracted less by the gravitational force than that at Paris, the clock at Cayenne ran slow.

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(5)Length of an Arc :

The length of a one-degree arc of a parallel of latitude and also the length of a one-degree arc of the meridian of longitude would be a constant value everywhere on the earth if the earth were a perfect sphere. At the equator, the former is 110 -58 km and the latter 111-32 km. Thus the length of 1° of latitude is almost the same as the length of 1° longitude at the equator and on average, the value of 111 km per degree may be accepted.

Actually, the length of a degree may be accepted. The length of a degree of latitude is not constant everywhere on the earth and 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 11 km longer at the poles and it proves that the earth is an oblate spheroid.

Question 4. Show how Eratosthenes calculated the circumference of the earth.

Answer.

Eratosthenes calculated the circumference of the earth as follows:

Eratosthenes who lived in the 3rd century B.C. in Egypt was actually a Greek geographer and astronomer. More than 2000 years ago, an Egyptian, by name of Eratosthenes, measured the circumference of the earth. He found that on June 21st, at a place called to scene in Egypt the sun’s rays reached the bottom of a deep well at 12 noon on that day. This indicated 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. Stadiums are an Egyptian unit measuring distance and is equivalent to about 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° -r 7°12′ = 50.

The distance between Alexandria and Syene is 5000 stadia. [. . 1 stadia = 150 metre or 625 stadia = 1 km]. Hence the length of the circumference of the earth was calculated by Eratosthenes as 5000 x 50 = 2,50,000 stadia or (2,50,000 -T- 625) stadia or 46,250 km. This approximate figure is quite close to the actual figure of 40,000 km.

Question 5. Prove the earth is spherical in nature.
Answer.
The following study reveals that Earth is round in shape :

Indirect Proofs :

(1)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 were flat, the sunrise would be everywhere at the same time.

(2)Sighting a ship:

An observer watching through a telescope the approach of a ship seas 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 proves the rounded shape of the earth.

(3)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. All heavenly bodies like the sun, moon and other planets appear circular in all positions. The earth and other heavenly bodies must be rounded and spherical in shape.

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Class 9 WBBSE Geography Question Answer

(4)Travelling Round the Earth :

As the earth is spherical in shape, it is possible to circumnavigate the earth. Magellan was the first to go around the earth in a ship and complete his voyage without encountering a sharp edge. An aeroplane can fly around the world. If we travel continually in the same direction, we return eventually to our starting point.

5) The Bedford Level Experiment:

An experiment was made many years ago in the Bedford Level Canal area in Britain. The water level of the canal provided the base of measurement. Three poles were fixed at intervals of about 5 km such that the poles were rising to the same height as the level of water in the canal.

When a telescope was placed that in such a way that the top of pole A was in line with of pole C, it was found that the line of sight was intersecting the middle of pole B. This would not happen if the earth were flat. The middle pole B appeared higher owing to the curvature of the earth.

 

(6)The spherical horizon :

The limit of the horizon at a place is circular and the horizon widens as the height of the observer increases. This again indicates the spherical shape of the Earth.

(7)Effect of gravity :

The weight of a substance is related to the effect of the force of gravity on that substance. It is found that an object weighs nearly the same at all places on the earth. This means that the force of gravity is nearly equal in all places. This is possible only when the earth is a sphere.

(8) Position of the Pole star:

The pole star appears vertically overhead at the North Pole. If the earth were flat, the pole star should be overhead at all places on the earth. This is not the case. The angle of elevation of the pole star is about 40° at London and 0° at Singapore or on the equator. This is possible only when the earth is spherical in shape.

Direct Proofs :

(1)Aerial Photographs :

The most striking evidence of the spherical shape of the earth is obtained from photographs taken from space. Pictures taken by satellites show the spherical shape of the earth. The astronauts from the moon have taken pictures of the earth showing its spherical shape.

(2)Artificial Satellites :

Artificial Satellites and many space probes are put in orbit on the assumption that the earth is spherical. The calculations have proved correct and the space probes of other planets of the solar system have provided valuable data.

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Question 6. What was the ancient concept regarding the shape of the earth? Discuss in brief.
Answer.

The ancient concept regarding the shape of the earth

Ancient Flat concept of shape of the Earth: The flat Earth model is an archaic belief that the earth’s shape is a plane or disk. Many ancient cultures have had conceptions of a flat earth, including Greece until the classical period, the Bronze Age and Iron Age civilizations of the Near East until the Hellenistic period, India until the Gupta period (early centuries AD) and China until the 17th century. Given below the important ancient flat concepts of the shape of the earth—

(1) Ancient Near East :

(1) The Jewish conception of a flat earth is found in biblical and post-biblical times.
(2)The early Egyptians and Mesopotamians thought that the world was portrayed as a flat disk floating in the ocean.
(3)A similar model is found in the Homeric account of the 8th century B.C. The biblical earth is a flat disc floating on water.

(2)Ancient Mediterranean :

Poets :
(1) Both Homer and
(2) Hesiod described a flat disc cosmography.

Philosophers :

Several presocratic philosophers believed that the earth was flat,
(1) Thales (550 BC) thought the earth floated in the water like a log. It has been argued, however, that Thales actually believe in a round earth,
(2) Anaximander (550 BC) believed that the earth was a short cylinder with a flat, circular top that remained stable because it was the same distance from all things,
(3) Anaximenes of Miletus believed that “the earth is flat and rides on air; in the same way the sun and the moon and the other heavenly bodies which are all fiery, ride the air because of their flatness,
(4) Xenophanes of colophon (500 BC) believed that the earth was flat, with its upper side touching the air, and the lower side extending without limit, (v) Belief in a flat earth continued into the 5th century B.C. Anaxagoras (450 B.C.) agreed that the earth was flat.

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Historians :

(1) Hecataeus of Miletus believed the earth was flat and surrounded by water,
(2) Herodotus in his histories ridiculed the belief that water encircled the world, yet most classicists agree he still believed the earth was flat because of his descriptions of literal “ends” or “edges” of the earth.

(3)Ancient India :

Ancient Jain and Buddhist cosmology held that the earth is a disc consisting of four continents grouped around a central mountain (Mount Meru) like the petals of a flower. An outer ocean surrounds these continents. This view of traditional Buddhist and Jain cosmology depicts the cosmos as a vast oceanic disk, founded by mountains, in which the continents are set as small islands.

(4)Norse and Germanic :

The ancient Norse and Germanic peoples believed in a flat earth cosmography of the earth surrounded by an ocean, with axis Mundi (a world tree: Yggdrasil, or pillar: Iraminsul) is the centre. The Norse believed that in the world-encircling ocean sat a snake called Jormungandr.

(5)Ancient China :

Ancient China, the prevailing belief was that the earth was flat and square, while the heavens were round, an assumption virtually unquestioned until the introduction of European astronomy in the 17th century.

WBBSE Solutions for Class 9 Geography and Environment

• Chapter 2 Movement Of The Earth Rotation & Revolution
• Chapter 3 Determination Of The Location Of A Place On Earth Surface
• Chapter 4 Geomorphic Processes And Land Forms Of The Earth
• Chapter 5 Weathering
• Chapter 6 Hazards And Disasters
• Chapter 7 Resources Of India
• Chapter 8 West Bengal
• Chapter 9 Map & Scale