Get textual answers, explanations, solutions, notes, extras, MCQs, PDF of Chapter 2 Movements of the Earth: 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
Long ago, many people believed that the Earth stood still and everything else, like the stars and planets, moved around it. This idea was called the geocentric view. Thinkers like Aristotle and Ptolemy supported this idea. However, this view changed when Galileo, using a telescope he invented, showed that the Earth actually moves around the Sun, just like other planets. This understanding is called the heliocentric view.
Over time, many astronomers helped us understand how planets move. Eudoxas created an early model of the solar system with Earth at the center. Aristarchus was one of the first to suggest the Sun was at the center. Nicolaus Copernicus later developed a detailed model showing the Sun at the center with planets, including Earth, orbiting it. Johannes Kepler discovered that planets move in elliptical, or oval-shaped, paths, not perfect circles. He also found that planets move faster when they are closer to the Sun and slower when they are farther away. Isaac Newton later explained these movements with his laws of motion and gravity.
The Earth has two main movements: rotation and revolution. Rotation is when the Earth spins on its own imaginary line, called an axis. This axis is tilted. The Earth rotates from west to east, completing one spin in about 24 hours. This spinning causes day and night. The side of the Earth facing the Sun has day, and the side facing away has night. The line separating day and night is called the circle of illumination. Rotation also affects the Earth’s shape, making it bulge slightly at the equator and flatten at the poles. It causes winds and ocean currents to curve, an effect known as the Coriolis effect. The speed of rotation is fastest at the equator and slowest at the poles. We don’t feel this movement because everything around us, including the air, moves with the Earth.
Revolution is the Earth’s movement around the Sun. The Earth travels in an elliptical path called an orbit, taking about 365 and a quarter days to complete one journey. This period is what we call a year. To account for the extra quarter day, we have a leap year every four years, adding an extra day to February. The Earth’s orbit is not a perfect circle, so its distance from the Sun changes. When the Earth is closest to the Sun, it’s called perihelion, and when it’s farthest, it’s aphelion.
The Earth’s revolution, combined with the tilt of its axis, causes the seasons. Because of the tilt, different parts of the Earth receive more direct sunlight.
Textual Questions, Answers (Oriental)
Multiple Choice Questions
Choose the correct answer from the brackets:
1. Summer solstice is experienced on
A. 4th July
B. 3rd January
C. 21st June
Answer: C. 21st June
2. Winter solstice is experienced on
A. 4th July
B. 22nd December
C. 3rd January
Answer: B. 22nd December
3. Days and nights are equal on
A. 21st March
B. 22nd December
C. 24th January
Answer: A. 21st March
4. Northern hemisphere experiences longest day and shortest night on
A. 23rd September
B. 21st June
C. 22nd December
Answer: B. 21st June
Choose the correct answer from the following [Knowledge based]
5. The spinning of the earth on its own polar axis is termed as―
A. revolution
B. rotation
C. annual movement
Answer: B. rotation
6. The speed of the earth’s rotation per wave at the equator is
A. 850km
B. 1120km
C. 1630km
Answer: C. 1630km
7. The sun rises in the east and sets in the west due to―
A. Rotation of the earth
B. Rotation of the sun
C. Revolution of the earth
Answer: A. Rotation of the earth
8. The date of Aphelion is
A. 2nd December
B. 4th July
C. 3rd January
Answer: B. 4th July
True and False
1. The rotation of the earth is responsible for the formation of days and nights.
Answer: True
2. 2009 A.D. is a leap year.
Answer: False
3. The distance between the sun and the earth is maximum on 3rd January.
Answer: False
4. 21st March is known as spring equinox.
Answer: True
Write very short notes on the followings
1. Vernal equinox?
Answer: The position on 21st March is known as Spring Equinox or Vernal Equinox. On this date, the earth is so located that both the poles are neither inclined towards the sun nor away from it, and the subsolar points lie on the equator.
2. Winter Solstice?
Answer: Winter Solstice occurs on December 22 when the subpolar points arrive at the Tropic of Capricorn (23½°S). On this day, the South Pole is inclined towards the sun, and the North Pole is away from it.
3. Ferrel’s Law?
Answer: Ferrel’s Law states that due to the effect of the Coriolis Force caused by the earth’s rotation, any object or fluid moving horizontally tends to be deflected. The law is named after the American climatologist William Ferrel who developed this concept in 1855.
4. Summer Solstice?
Answer: Summer Solstice occurs on June 21. On this day, the northward apparent migration of the sun is completed, and the sun is directly overhead at 23½°N Latitude (Tropic of Cancer). This position of the earth, when the sun shines vertically on the Tropic of Cancer, is called Summer Solstice.
5. Leap Year?
Answer: A leap year is a year of 366 days that occurs after every four years. Normally, a year is 365 days, but the Earth takes about 365 days and 6 hours (specifically 5 hours 48 minutes 45.51 seconds) to revolve around the sun. Leaving off about 6 hours each year accumulates to about 24 hours, or one day, every four years. This extra day is added to February, making it 29 days long in a leap year.
6. Write a very short note on Autumnal Equinox.
Answer: On 23rd September, the position of the earth is so located that both the poles are neither inclined towards the sun nor are they away from it. The rays of the sun fall vertically on the equator. As a result, days and nights are of equal length throughout the world. This day is known as Autumn Equinox.
7. Write a very short note on Perihelion.
Answer: Perihelion is the position in the Earth’s orbit when the Earth is closest to the sun, which occurs on January 3.
8. Write a very short note on Earth’s orbit.
Answer: The path of the earth round the sun is called Earth’s orbit. The plane on which the earth moves is called the plane of orbit, or orbital plane. The Earth’s orbit is slightly elliptical in shape, not a circle, and the sun is situated in one focus of the ellipse. The length of the Earth’s orbit around the sun is about 96.5 crore km. Both the centres of the sun and the earth lie on the same orbital plane.
9. Write a very short note on Coriolis Force.
Answer: The Coriolis force is a tendency of deflection of wind and other moving objects like ocean currents due to the earth’s rotation. Earth’s rotation produces this force, which tends to turn the flow of air. This deviation from a straight path is called the Coriolis effect or Coriolis force.
10. Write a very short note on Kepler’s Law.
Answer: Johannes Kepler, a German astronomer, derived, formulated, and verified the three basic laws of planetary motion. Kepler’s Laws of Planetary Motion are:
(i) The path of each planet around the sun is an ellipse with the sun at one focus.(ii) The “area rule”: A planet covers equal areas of its orbit in equal periods of time.
(iii) The period of revolution of a planet is proportional to its distance from the sun, i.e., it travels most rapidly when it is nearest the sun and most slowly when it is farthest from the sun.
Answer in very short
1. Who first promulgated the idea of the rotation of the earth?
Answer: In 1522 A.D., Nicolaus Copernicus, a Polish astronomer proved first in his book titled “On the Revolutions of the Heavenly spheres” that the earth spins daily on its axis. Copernicus proposed that the Earth rotates, which better explained the daily motions of the heavens.
2. What do you know about the earth’s axis?
Answer: Rotation is the turning around of the Earth on its axis, from west to east. The axis is the imaginary line passing through the centre of the Earth on which the Earth rotates. The Earth spins, west to east, around its axis once in 24 hours. The north pole and south pole lie at the ends of the axis. The earth’s axis is not vertical. It makes an angle of 23½° with the vertical or 66½° with the plane of the Earth’s orbit. The Earth’s axis always remains pointed in the same direction (towards the Pole star) as the Earth journeys around the sun. The tilt of the Earth’s axis is also known as the inclination of the Earth’s axis.
3. In what way does the earth rotate?
Answer: The earth spins on its own imaginary axis from west to east. If we look down upon the Earth (Globe) from outside, the Earth is found to rotate from west to east or in anticlockwise direction. Since the Earth rotates in a west-east direction, we see the sun rising everyday in the east and setting in the west.
4. How much time does the earth take to complete one rotation?
Answer: The earth takes 24 hours to complete one rotation. More precisely, the earth spins on its own imaginary axis once in every 24 hours (actually 23 hours 56 minutes and 4 seconds).
5. What causes day and night on earth?
Answer: The rotation of the earth causes the formation of day and night. The earth rotates around its axis from west to east once in 24 hours. So when a particular place comes in front of the sun, it gets the sunlight and therefore experiences day. As the earth rotates, this particular place moves away from the sun into darkness. In this way, all places on the earth’s surface continuously experience periods of daylight followed by periods of darkness called night. The imaginary line that separates the lit-up half from the darkened half is called the circle of Illumination or Shadow circle.
6. What is the angle of inclination of the earth in its axis?
Answer: The earth’s axis is not vertical. It makes an angle of 23½° with the vertical or 66½° with the plane of the Earth’s orbit. The tilt of the Earth’s axis is also known as the inclination of the Earth’s axis.
7. Is the earth’s axis vertical?
Answer: The earth’s axis is not vertical.
8. What is the speed of rotation at the equator?
Answer: The speed of rotation at 0° (Equator) is 1670 km/hour.
9. What is the speed of rotation at Kolkata?
Answer: The speed of rotation at 22°34′ N (Kolkata) is 1536 km/hour.
10. Name the place (latitude) where days and nights are always equal?
Answer: Except at the Equator, days and nights are not equal on all the places of the earth. Daylight hours vary least at the equator, where there is 12 hours of day light throughout the year.
Answer the following questions briefly
1. Who first promulgated the idea of the rotation of the earth?
Answer: In 1522 A.D., Nicolaus Copernicus, a Polish astronomer proved first in his book titled “On the Revolutions of the Heavenly spheres” that the earth spins daily on its axis. Copernicus proposed that the Earth rotates, which better explained the daily motions of the heavens.
2. What do you know about the earth’s axis?
Answer: Rotation is the turning around of the Earth on its axis, from west to east. The axis is the imaginary line passing through the centre of the Earth on which the Earth rotates. The Earth spins, west to east, around its axis once in 24 hours. The north pole and south pole lie at the ends of the axis. The earth’s axis is not vertical. It makes an angle of 23½° with the vertical or 66½° with the plane of the Earth’s orbit. The Earth’s axis always remains pointed in the same direction (towards the Pole star) as the Earth journeys around the sun. The tilt of the Earth’s axis is also known as the inclination of the Earth’s axis.
3. In what way does the earth rotate?
Answer: The earth spins on its own imaginary axis from west to east. If we look down upon the Earth (Globe) from outside, the Earth is found to rotate from west to east or in anticlockwise direction. Since the Earth rotates in a west-east direction, we see the sun rising everyday in the east and setting in the west.
4. How much time does the earth take to complete one rotation?
Answer: The earth takes 24 hours to complete one rotation. More precisely, the earth spins on its own imaginary axis once in every 24 hours (actually 23 hours 56 minutes and 4 seconds).
5. What causes day and night on earth?
Answer: The rotation of the earth causes the formation of day and night. The earth rotates around its axis from west to east once in 24 hours. So when a particular place comes in front of the sun, it gets the sunlight and therefore experiences day. As the earth rotates, this particular place moves away from the sun into darkness. In this way, all places on the earth’s surface continuously experience periods of daylight followed by periods of darkness called night. The imaginary line that separates the lit-up half from the darkened half is called the circle of Illumination or Shadow circle.
6. What is the angle of inclination of the earth in its axis?
Answer: The earth’s axis is not vertical. It makes an angle of 23½° with the vertical or 66½° with the plane of the Earth’s orbit. The tilt of the Earth’s axis is also known as the inclination of the Earth’s axis.
7. Is the earth’s axis vertical?
Answer: The earth’s axis is not vertical.
8. What is the speed of rotation at the equator?
Answer: The speed of rotation at 0° (Equator) is 1670 km/hour.
9. What is the speed of rotation at Kolkata?
Answer: The speed of rotation at 22°34′ N (Kolkata) is 1536 km/hour.
10. Name the place (latitude) where days and nights are always equal?
Answer: Except the Equator, days and nights are not equal on all the places of the earth. Daylight hours vary least at the equator, where there is 12 hours of day light throughout the year.
Answer the following questions briefly
1. What are the causes of seasons?
Answer: The main causes of the change of seasons are:
(i) Elliptical Orbit of the earth,
(ii) Location of the Axis on same direction,
(iii) Spherical shape of the Earth,
(iv) Differentiation of temperature according to increasing and decreasing length of Day and Night,
(v) Differentiation of temperature according to Vertical and Lateral rays of the sun.
Additionally, the variation in the length of days and nights, which contributes to seasons, is caused by (i) spherical shape of the earth, (ii) rotation and revolution of the earth, (iii) elliptical shape of the earth’s orbit, (iv) tilting of the earth’s axis at 66½° to the orbital plane and (v) parallelism of the earth’s axis.
2. How are the days and nights caused on the earth’s surface?
Answer: The earth rotates around its axis from west to east once in 24 hours. As the earth is a sphere, only half of it facing the sun is lit-up by sunrays. The other half remains dark. As a result, day occurs in the lit-half of the earth and night in the dark-half of it. When a particular place comes in front of the sun, it gets the sunlight and therefore experiences day. As the earth rotates, this particular place moves away from the sun into darkness, experiencing night. The earth’s rotation does not allow either of the two halves to remain always lit or unlit. They keep moving from sunlight to darkness and again from darkness to sunlight after almost regular intervals. The imaginary line that separates the lit-up half from the darkened half is called the circle of Illumination or shadow circle.
3. What is Ferrel’s law?
Answer: Ferrel’s law states: Any object or fluid moving horizontally in the northern hemisphere tends to be deflected to the right of its path of motion, regardless of the compass direction of the path. In the Southern hemisphere, a similar deflection is toward the left of the path of motion. This deflection is due to the coriolis force produced by the earth’s rotation. According to Ferrel, due to the effect of Coriolis Force, wind and ocean currents are deflected towards the right in the northern hemisphere and towards the left in the southern hemisphere.
4. What is the difference between the earth’s rotation and revolution?
Answer: The major differences between Rotation and Revolution are:
| Rotation | Revolution |
| (i) Spinning around of the earth in its own axis. | (i) Movement of the earth around the sun on its orbit. |
| (ii) The earth takes 24 hour to complete one rotation. | (ii) The earth takes 365.25 days to complete one revolution. |
| (iii) Rotation causes day and night. | (iii) Revolution causes seasons. |
| (iv) Rotation is also called the diurnal motion of the earth. | (iv) Revolution is also called annual motion of the earth. |
| (v) The earth is spinning on its own axis. | (v) The earth revolves round the sun on its elliptical orbit. |
5. What is Leap Year?
Answer: Normally a year is considered to be of 365 days, while the actual period of earth’s one revolution round the sun is 365 days and a little less than 6 hours (5 hours 48 minutes and 45.51 seconds). This means we leave off about 6 hours every year. Evidently in four years, we leave off about 6 x 4 = 24 hours or one day. So, we have a year of 366 days after every four years. Such a year is called a leap year. A year, divisible by 4, is treated as a leap year; for example 1984, 1988, 1992, 1996, 2004 etc.
In a leap year, February has 29 days instead of 28 days. However, to correct for the fact that the period left off in four years is slightly less than 24 hours, the only century years or the years those ending in ’00 are divisible by 400 are leap years. So 2000, 2400, 2800 etc. are leap years. The other century years are not considered to be leap years.
6. What do you mean by Aphelion and perihelion?
Answer: The distance between the earth and the sun is not constant because the orbit is not circular in shape, it is an ellipse, and the sun is not centrally placed within it.
Aphelion refers to the position when the distance between the sun and the earth is the farthest. This occurs on July 4, and the distance is about 15 crore 20 lakh km. In Greek ‘ap’ means ‘away from’ and ‘helios’ means ‘Sun’. The Earth moves slowest in aphelion.
Perihelion refers to the position when the earth is closest to the sun. This occurs on January 3, and the distance is about 14 crore 70 lakh km. At the perihelion position, the distance between the sun and the earth becomes minimum and the sun looks bigger than at aphelion. The Earth moves fastest when it is in perihelion.
7. What do you understand by the rotation and the revolution of the earth?
Answer: The earth has two main motions or movements: Rotation and Revolution.
Rotation is the spinning of the earth on its own imaginary axis from west to east. This spinning is also termed ‘diurnal motion’ or ‘the daily movement of the earth’. The earth takes about 24 hours (actually 23 hours 56 minutes and 4 seconds) to complete one rotation. Rotation causes the formation of day and night.
Revolution is the movement of the earth around the sun from west to east in an elliptical orbit. This movement is also known as the Annual Movement of the earth. It takes about 365 days 5 hours 48 minutes and 46 seconds (approximately 365¼ days) to complete one round about the sun. Revolution, along with the tilt of the Earth’s axis, causes the change of seasons.
8. What are the effects of revolution of the globe?
Answer: The effects of the earth’s revolution are:
- Variation in the length of day and nights,
- Change of seasons,
- Idea of a year and leap year formed.
- Sun’s apparent annual movement,
- Idea of the latitudes and heat-zones of the earth formed.
- Shifting of wind belts.
Revolution also causes seasons and is called the annual motion of the earth.
Essay Type Questions
1. How are days and nights caused on the earth?
Answer: The earth rotates around its axis from west to east once in every 24 hours. As the earth is a sphere, only half of it facing the sun is lit-up by sunrays, while the other half remains dark. As a result, day occurs in the lit-half of the earth and night in the dark-half of it. When a particular place comes in front of the sun due to rotation, it gets the sunlight and therefore experiences day. As the earth continues to rotate, this particular place moves away from the sun into darkness, experiencing night. The earth’s rotation does not allow either of the two halves to remain always lit or unlit; they keep moving from sunlight to darkness and again from darkness to sunlight after almost regular intervals. The imaginary line that separates the lit-up half from the darkened half is called the circle of Illumination or shadow circle. In this way, all places on the earth’s surface continuously experience periods of daylight followed by periods of darkness called night. During each 24 hour day, each place or meridian appears to shift its position from west to east, making the sun appear to move from east to west.
2. Give three proofs of diurnal motion of the earth.
Answer: There are many ways to prove that the earth rotates continuously on its axis from the west to east. Three proofs are:
- East-west movement of the sun: Since the earth rotates from west to east, we see the sun rising in the east and setting in the west. Not only the sun, but all heavenly bodies in the sky seem to move from east to west everyday.
- Drop of stone from high tower: At the time when there is no movement of air, if a piece of stone is dropped from a high tower, it will fall on the ground slightly to the east than the vertical. This happens because the earth rotates from west to east and the rotational velocity of the stone (at the tower) is greater than the earth’s surface below. This proves both the earth’s west-eastward rotation and that the speed of rotation is greater where the circumference is larger. This proof was conducted in Boulogne (France) and Humburg (Germany) from a 76.2m high tower.
- Foucault’s Pendulum Experiment: In 1851, Jean Bernard Leon Foucault provided an excellent proof of earth’s rotation. He suspended a heavy cannon ball from the dome of the Pantheon in Paris using a long wire. A pin attached to the bottom traced lines in sand below as it swung north-south. As time passed, the pendulum was seen oscillating in a line different from what it was tracing at the outset. It was obvious that the earth’s surface was slowly turning below the pendulum, but this motion was not being transmitted to the ball. This showed that the earth was slowly turning from west to east as it rotates round the axis.
3. Explain the effects of the earth’s rotation.
Answer: The rotation of the earth is responsible for the following major effects:
- Formation of Days and Nights: Rotation causes different parts of the Earth to face towards or away from the sun, resulting in periods of daylight and darkness.
- Occurrence of Sunrise, Noon and Sunset: As the earth rotates west to east, the sun appears to rise in the east, reach its highest point at noon, and set in the west.
- Determination of time: The Earth takes a full day (approximately 24 hours) to complete one rotation, which forms the basis for our system of timekeeping.
- Deflection of Planetary Wind and Ocean Currents (Coriolis Effect): Rotation causes moving air (wind) and water (ocean currents) to be deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere (Ferrel’s Law). This affects general circulation patterns, cyclones, and anti-cyclones.
- Formation of Tides: The daily rise and fall of tides are partly a result of the Earth’s rotation, as places on the surface are brought into positions where the Moon’s gravitational pull causes ocean water to swell.
- Magnetization of the Earth: The Earth’s magnetic field is partly due to its rotation and the circulation of molten rock in its outer core.
- Differentiation of Temperature: Rotation causes variations in the distribution of temperature across the Earth’s surface as different areas receive sunlight.
- Determination of the Direction: As the earth rotates west to east, the first direction of east where the sun rises becomes prime, helping determine other directions.
- Different local time: Due to rotation, different places on Earth have different local times simultaneously.
- Shape of the Earth: Rotation is considered responsible for the slight flattening of the Earth at the poles and a bulging at the equator, making it an oblate spheroid. The equatorial diameter is 43km longer than the polar diameter.
- Other effects: These include the variation of daily temperature, determination of Longitude, indirect influence on the creation of pressure belts, and the creation and expansion of life.
4. Give at least three proofs supporting the annual motion of the earth.
Answer: The annual motion of the Earth, or its revolution around the Sun, is supported by several observable phenomena which serve as proofs. Three of these are:
- Change of Seasons: The progression through spring, summer, autumn, and winter occurs because the Earth revolves around the Sun with its axis tilted. This tilt causes different hemispheres to receive more direct sunlight at different times of the year, leading to seasonal variations in temperature and weather patterns.
- Variation in the length of day and nights: Throughout the year, the length of daylight and nighttime changes for most locations on Earth (except at the equator). This variation, including phenomena like the longest day (summer solstice) and shortest day (winter solstice), is a direct consequence of Earth’s revolution combined with its axial tilt.
- Sun’s apparent annual movement: Due to the Earth’s revolution, the Sun appears to move north and south between the Tropic of Cancer and the Tropic of Capricorn over the course of a year. This apparent migration (Uttarayan and Dakshinayan) causes the overhead position of the sun to change, which wouldn’t happen if the Earth didn’t revolve around the sun.
5. Describe briefly how the earth’s rotation and revolution affect life on earth.
Answer: The Earth’s rotation and revolution profoundly affect life on Earth in several ways.
Rotation causes the cycle of day and night, which governs the fundamental rhythms of activity and rest for most plants and animals. Photosynthesis in plants, for example, depends on daylight. Rotation also drives the Coriolis effect, influencing wind and ocean currents, which shape global climate patterns and marine ecosystems, thereby determining habitats suitable for life. The tides, partly caused by rotation, affect coastal life. Furthermore, rotation contributes to the Earth’s magnetic field, shielding life from harmful solar radiation.
Revolution around the Sun causes the change of seasons. These seasonal shifts in temperature, rainfall, and daylight hours dictate life cycles for many species, including plant growth, animal migration, hibernation, and reproduction. The variation in the length of day and night throughout the year, caused by revolution and the Earth’s axial tilt, also influences biological processes like flowering in plants and breeding patterns in animals. Together, rotation and revolution create the diverse environmental conditions and cyclical changes that life on Earth has adapted to and depends upon. Rotation also has an indirect influence on the creation and expansion of life.
6. Explain the phenomena of the change of season.
Answer: The change of seasons is primarily caused by the combination of the Earth’s revolution around the Sun and the tilt of its rotational axis (at 23½° to the vertical or 66½° to its orbital plane), along with the parallelism of the axis (meaning the axis always points in the same direction towards the Pole Star). As the Earth revolves around the Sun in its elliptical orbit, its tilted axis means that different parts of the Earth receive the Sun’s rays more directly at different times of the year.
When the Northern Hemisphere is tilted towards the Sun (around June 21st, the Summer Solstice), it receives more direct sunlight, resulting in longer days, shorter nights, and warmer temperatures (summer). At the same time, the Southern Hemisphere is tilted away from the Sun, experiencing shorter days, longer nights, and colder temperatures (winter).
Conversely, when the Southern Hemisphere is tilted towards the Sun (around December 22nd, the Winter Solstice), it experiences summer, while the Northern Hemisphere experiences winter.
During the Equinoxes (around March 21st – Vernal Equinox, and September 23rd – Autumnal Equinox), neither pole is tilted significantly towards or away from the Sun. The Sun’s rays fall vertically on the equator, and days and nights are approximately equal in length all over the Earth. These periods mark the transition between summer and winter (spring and autumn).
Therefore, the change of seasons is a result of the varying amounts of solar energy received by different parts of the Earth throughout its annual journey around the Sun, due to its axial tilt and revolution.
7. Explain the effects of the earth’s revolution.
Answer: The revolution of the Earth, which is its movement around the Sun in an elliptical orbit approximately every 365.25 days, has several significant effects:
- Variation in the length of day and nights: Combined with the Earth’s axial tilt, revolution causes the length of daylight and darkness to vary throughout the year at different latitudes. This leads to phenomena like solstices (longest/shortest days) and equinoxes (equal day/night).
- Change of seasons: As the Earth revolves with its tilted axis, different hemispheres are oriented towards or away from the Sun at different times, causing the cycle of seasons (spring, summer, autumn, winter) due to variations in solar energy received.
- Idea of a year and leap year formed: One complete revolution defines the length of a year (approximately 365 days, 5 hours, 48 minutes, 46 seconds). To account for the extra fraction of a day, a leap year with 366 days is added every four years.
- Sun’s apparent annual movement: Revolution causes the Sun to appear to migrate north and south between the Tropic of Cancer (23½°N) and the Tropic of Capricorn (23½°S) over the course of the year. This apparent movement is known as Uttarayan (northward) and Dakshinayan (southward).
- Idea of the latitudes and heat-zones of the earth formed: The varying angle of the Sun’s rays due to revolution and tilt leads to different heat zones on Earth (Tropical, Temperate, Polar) based on latitude, influencing climate.
- Shifting of wind belts: Seasonal changes caused by revolution lead to the shifting of global pressure and wind belts north and south during the year.
- Aphelion and Perihelion: Because the Earth’s orbit is elliptical, the distance between the Earth and Sun varies. The Earth is farthest from the Sun (Aphelion) around July 4th and closest (Perihelion) around January 3rd. This affects the speed of revolution (fastest at perihelion, slowest at aphelion) according to Kepler’s laws.
Extras
Additional MCQs
1. Which model places Earth at the centre of the universe?
A. Geocentric
B. Heliocentric
C. Elliptical
D. Equatorial
Answer: A. Geocentric
60. Magnetization of Earth is partly due to its rotation and partly to circulation of what?
A. Ocean currents
B. Molten rock
C. Atmospheric winds
D. Solar radiation
Answer: B. Molten rock
Additional Questions, Answers
1. What is geocentric theory?
Answer: Many ancient and medieval cultures believed the stars and the planets rotated around a fixed Earth, and this type of concept was known as geocentric ideas. Ancient Greek astronomer Aristotle’s view was of a stationary earth at the center of a revolving universe. This geocentric worldview became engrained in Christian theology, making it a doctrine of religion as much as natural philosophy. Greek astronomer Ptolemy (2nd century A.D.) began by accepting the view that the earth does not move, but is the centre of the universe.
70. Describe in detail the changes that occur during equinoxes.
Answer: On September 23 and March 21 the earth is so located on these two dates that the subsolar points lie on the equator. The shadow circle passes through both the poles and coinsides with meridians. Thus these phenomena cause day and night equal all over the earth on these two dates 23rd Sept. and 21st March. On these days the positon of the earth is so located that both the poles neither inclined towards the sun nor they are away from it. The rays of the sun fall vertically on the equator. As a result, days and nights are of equal length throughout the world. Hence when it is spring (as on March) in the northern hemisphere, it is autumn in southern hemisphere. 21st March is known as Spring Equinox and 23rd September is known as Autumn Equinox. At the equinoxes, days and nights are of equal length throughout the world.
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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