Rotation and Revolution: ICSE Class 9 Geography solutions
Get notes, summary, solutions, questions and answers, MCQs, extras, and PDFs of Chapter 3 “Rotation and Revolution” which is part of ICSE Class 9 Geography (Morning Star/Total) textbook/workbook answers. However, the notes should only be treated as references and changes should be made according to the needs of the students.
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Summary
Our Earth moves in two main ways. It spins like a top, and it also travels around the Sun. These movements are called rotation and revolution. They cause many things we see, like day and night, and the changing seasons.
Rotation is when the Earth spins on its axis. This axis is an imaginary line going through the North Pole and the South Pole. The Earth spins from west to east, taking about 24 hours to complete one spin. This spinning is what causes day and night. As Earth spins, different parts of it face the Sun (daytime) and then turn away from the Sun (nighttime). The Earth’s axis is not straight up and down. It is tilted at an angle of 23½° from a vertical line. This tilt is always pointed in the same direction, towards the Pole Star, as Earth moves. Rotation also makes the Sun, Moon, and stars appear to move across the sky from east to west. It’s like when you are in a moving train and trees outside seem to move backward. Another effect is the Coriolis effect, which changes the direction of winds and ocean currents. The speed of rotation is fastest at the Equator.
Revolution is the Earth’s journey around the Sun. Earth travels in a path called an orbit, which is shaped like a slightly flattened circle, an ellipse. It takes Earth about 365 days and 6 hours to go all the way around the Sun once. This is why we have a year. The extra 6 hours each year add up, so every four years, we have a leap year with an extra day. As Earth revolves around the Sun, its tilted axis causes the seasons. For part of the year, the North Pole is tilted towards the Sun, bringing summer to the Northern Hemisphere. When it’s tilted away, it’s winter there. The seasons are opposite in the Southern Hemisphere. If Earth’s axis were not tilted, there would be no seasons, and every day would have equal hours of daylight and night everywhere. We don’t feel these movements because gravity holds us and everything on Earth firmly, keeping us moving with the planet.
Because of the tilt and revolution, the length of day and night changes throughout the year, except at the Equator where they are always nearly equal. There are special days marking these changes. Solstices happen twice a year. Around June 21st, the Northern Hemisphere has its longest day (summer solstice). Around December 22nd, it has its shortest day (winter solstice). On these days, the Sun appears to stand still in its noon height before reversing direction. Equinoxes also happen twice a year, around March 21st and September 23rd. On these days, day and night are of equal length all over the world because the Sun shines directly over the Equator. The word Equinox means ‘equal night’.
The Sun’s rays hit Earth differently because of its tilt. Areas near the Equator (Torrid Zone) get direct rays and are warm. Areas further north and south (Temperate Zones) get slanting rays and have milder climates. The polar regions (Frigid Zones) get very slanting rays and are very cold. Even when the Sun is just below the horizon before sunrise or after sunset, we see some light. This is called twilight (at dusk) or dawn. This diffused light is caused by sunlight scattering in the atmosphere. The duration of twilight is shorter at the Equator and gets longer towards the poles.
Textbook solutions (Morning Star/Total)
Multiple-Choice Questions
1. Which of the following is true about the rotation of the earth?
(a) The earth completes one rotation in 25:56:4.09 hrs
(b) The earth’s axis passes through the poles
(c) The speed of rotation increases as we move towards the equator
(d) All of the above.
Answer: (b) The earth’s axis passes through the poles
2. What angle does the earth’s axis make with the plane of earth’s orbit?
(a) 0°
(b) 23½°
(c) 66½°
(d) 90°
Answer: (c) 66½°
3. An apparent outward force that acts on a rotating object:
(a) Centrifugal Force
(b) Sunset Effect
(c) Coriolis Effect
(d) Rotational Effect
Answer: (a) Centrifugal Force
4. What is the shape of the path of the earth around the sun?
(a) Oval path
(b) Spherical path
(c) Elliptic
(d) Coriolis
Answer: (c) Elliptic
5. Which of the following is correct?
(a) Aphelion: earth is closest to the sun
(b) Aphelion: earth is farthest from the sun
(c) Aphelion: moon is closest to the earth
(d) Aphelion: the equator is closest to the sun.
Answer: (b) Aphelion: earth is farthest from the sun
6. What is the time difference between two consecutive lines of longitude?
(a) 7½ minutes
(b) 4 minutes
(c) 1 minute
(d) 3 minutes
Answer: (b) 4 minutes
7. Which of the following is true about the revolution of the earth around the sun?
(a) It results in the cycle of seasons
(b) The direction of motion is the same as rotation
(c) The speed is not uniform
(d) All of the above.
Answer: (d) All of the above.
8. Which of the following is true about the perihelion position of the earth?
(a) It is farthest from the sun.
(b) It occurs on 3 January.
(c) The speed of revolution is the least.
(d) All of the above.
Answer: (b) It occurs on 3 January.
9. The lighted part of the earth is called the ______________
(a) Circle of Light
(b) Circle of Illumination
(c) Circle of Solstice
(d) Circle of Equinox
Answer: (b) Circle of Illumination
10. Perihelion : 147.4 million km :: ______________ : 152 million km
(a) Aphelion
(b) Equinox
(c) Solstice
(d) All of the above.
Answer: (a) Aphelion
11. Which of the following is true about the aphelion?
(a) Occurs on 4 July.
(b) Summer in northern hemisphere
(c) Speed of revolution is maximum
(d) All of the above.
Answer: (a) Occurs on 4 July.
12. Solstice : Summer/Winter :: ______________ : Spring/Autumn
(a) Solstice
(b) Equinox
(c) Vernal
(d) None of the above.
Answer: (b) Equinox
13. Name the phenomenon when the regions beyond the Arctic Circle experience 24 hours daylight.
(a) Daylight sun
(b) Midnight sun
(c) Arctic sun
(d) Regional sun
Answer: (b) Midnight sun
14. The period of diffused light between sunset and complete darkness is called
(a) dawn
(b) dusk
(c) twilight
(d) Both (b) and (c)
Answer: (d) Both (b) and (c)
15. The duration of twilight:
(a) increases to the poles
(b) might last for as much as 7 weeks at the poles
(c) is as long as the sun is 18° below the horizon
(d) all of the above.
Answer: (d) all of the above.
16. World Standard Time : 0° :: Indian Standard Time : ______________
(a) 23½°
(b) 72½°
(c) 66½°
(d) 82½°
Answer: (d) 82½°
17. Greenwich Mean Time : ______________ :: Indian Standard Time : 12:00 pm
(a) 6:30 am
(b) 5:30 am
(c) 6:30 pm
(d) 5:30 pm
Answer: (a) 6:30 am
18. World Standard Time : ______________ :: Indian Standard Time : Standard Meridian of India
(a) World Standard Meridian
(b) Prime Meridian
(c) International Date Line
(d) Greenwich Mean Time
Answer: (b) Prime Meridian
Short Answer Questions
1. What is meant by the inclination of earth’s axis? At what angle is the earth’s axis inclined?
Answer: The angle at which the earth is tilted is known as the inclination of the earth’s axis. The earth’s axis is not vertical; it makes an angle of 23½° with the vertical. This means that if a line were drawn parallel to the plane of the earth’s orbit, the axis would make an angle of 66½° to this line. The axis is, therefore, inclined at an angle of 23½° from the perpendicular to the plane of the Earth’s orbit.
2. Name the two chief motions of the earth.
Answer: Rotation and revolution are the two chief motions of the earth.
3. Describe two characteristics of rotation.
Answer: Two characteristics of rotation are:
(i) Direction: The earth completes one rotation from west to east on its axis in 23 hours, 56 minutes, 4.09 seconds, which is roughly in 24 hours.
(ii) Speed: The speed of earth’s rotation at the Equator is 1670 km per hour, as the circumference of the earth is 40,075 km, which is covered in 24 hours. The speed decreases towards the poles.
4. State two effects of the rotation of the earth.
Answer: Two effects of the rotation of the earth are:
(i) The occurrence of Day and Night is caused by the rotation of the earth on its axis.
(ii) Sunrise and Sunset are caused by the rotation of the earth from west to east, as every part of the earth’s surface faces the sun at some time or the other.
5. Mention any two possible consequences if the axis of the earth was vertical instead of inclined.
Answer: If the axis of the earth was vertical instead of inclined, two possible consequences would be:
(i) At all places on the earth, the length of day and night would have been equal.
(ii) Places on earth would have the same temperature throughout the year, and there would also be no seasons.
6. State one reason why we do not feel the motions of the earth.
Answer: We do not feel the motions of the earth because the force of gravity keeps everything attached to the earth. This keeps all objects at rest with reference to the motions of the earth.
7. What is an elliptic?
Answer: The path of the earth around the sun is known as elliptic. It passes through the centre of both the earth and the sun.
8. Define ‘revolution’.
Answer: The earth, like all other planets in the Solar System, revolves round the sun in an elliptical orbit. This motion of the earth is known as revolution.
9. State two chief characteristics of the revolution of the earth.
Answer: Two chief characteristics of the revolution of the earth are:
(i) The earth moves round the sun in an elliptical orbit at an average speed of 29.8 kilometres per second or about 100,000 kilometres per hour.
(ii) The period taken by the earth to make one complete round of the sun is 365 days, 5 hours, 48 minutes and 45.51 seconds, which is taken as 365 days and 6 hours. The length of one Solar year is 365 days.
10. Mention two effects of revolution.
Answer: Two effects of revolution are:
(i) Seasonal Changes: Revolution causes different seasons, i.e., the changing weather conditions due to differences in the heating of the earth. Revolution is an annual cycle, so the seasons repeat year after year.
(ii) Creation of heat zones: The spherical shape of the earth along with its movements around the sun causes the difference in the angles at which the sun’s rays fall on the earth’s surface. This causes difference in the distribution of heat on the earth’s surface, and as a result, the world has been divided into three distinct heat or temperature zones.
11. What do you understand by perihelion and aphelion?
Answer: Due to the elliptical orbit of the earth, the distance between the earth and the sun varies. When the earth is closest to the sun, the position is called perihelion, and when it is farthest, the position is called aphelion. At aphelion, the distance of the sun is 152 million km, while at its closest at perihelion, the earth is 147.3 million km away from the sun. On January 3, the earth in its orbit is closest to the sun; this time is said to be Perihelion. On about July 4, the earth is farthest from the sun; at this time, the earth is said to be Aphelion.
12. On which two days are the days and nights equal all over the world and why? What name do you give to these days?
Answer: The days and nights are equal all over the world on 21st March and 23rd September. This is because on these two days in a year, the sun shines vertically over the Equator. These days are known as Equinoxes; 21st March is the Spring or Vernal Equinox, and 23rd September is the Autumnal Equinox.
13. Which is the longest and which is the shortest day in the Northern Hemisphere and why?
Answer: In the Northern Hemisphere, the longest day is June 21st. This is because on this day, the North Pole is tilted towards the sun, and the sun is overhead at the Tropic of Cancer. The shortest day in the Northern Hemisphere is December 22nd. This is because on this day, the Northern Hemisphere is tilted away from the sun, while the Southern Hemisphere is tilted towards the sun.
14. On which dates does the sun shine vertically overhead at (a) Equator, (b) Tropic of Cancer. (c) Tropic of Capricorn?
Answer: The sun shines vertically overhead at:
(a) Equator on 21st March and 23rd September.
(b) Tropic of Cancer on June 21st.
(c) Tropic of Capricorn on December 22nd.
15. Why is noon is hotter than morning?
Answer: Noon is hotter than morning because at noon, the sun is overhead. When a place receives vertical sun rays, the place gets hot. This is because the amount of heat in the direct vertical rays is concentrated on a small area, whereas in the morning, the sun’s rays are more oblique, and the same amount of heat is spread over a larger area.
16. Why are days and nights equal at all places on earth on September 23? What are the seasons in the Northern and the Southern Hemispheres on this date?
Answer: On September 23rd, days and nights are equal at all places on earth because on this day, the sun is vertically overhead at the Equator. On this date, it is autumn in the Northern Hemisphere and spring in the Southern Hemisphere.
17. What is meant by Summer Solstice? When do we have Summer Solstice in the Northern Hemisphere?
Answer: Summer Solstice refers to the time when, on June 21, the earth is in the position where the North Pole is tilted towards the sun, and on this day, the sun is overhead at the Tropic of Cancer. We have Summer Solstice in the Northern Hemisphere on June 21.
18. What is meant by Equinox?
Answer: Equinox refers to the time when the sun crosses the plane of the earth’s Equator, making night and day of equal length. This occurs on two days in a year, 21st March (Spring or Vernal Equinox) and 23rd September (Autumnal Equinox), when the sun shines vertically over the Equator and days and nights are of equal length throughout the world.
19. What will be the duration of daylight on March 21st at 23°30′N and 66°30’S latitudes? Give reason.
Answer: On March 21st, the duration of daylight at 23°30′N and 66°30’S latitudes will be 12 hours. The reason is that March 21st is an Equinox, and at the Equinoxes, the days and nights are of equal length throughout the world because the sun shines vertically over the Equator.
20. What is the relationship of seasons between the Northern and Southern Hemispheres?
Answer: The seasons in the Northern and Southern Hemispheres are reversed. For example, when it is summer in the Northern Hemisphere, it is winter in the Southern Hemisphere. On March 21, it is spring in the Northern Hemisphere and autumn in the Southern Hemisphere. On September 23, it is autumn in the Northern Hemisphere and spring in the Southern Hemisphere.
21. Briefly describe the cycle of seasons with the change in inclination of the sun’s rays. Which temperature zone receives almost vertical rays of the sun and which zones receive slanting rays?
Answer: Revolution of the earth causes different seasons, which are changing weather conditions due to differences in the heating of the earth; this is an annual cycle. The amount of heat a place receives depends on the angle at which the sun’s rays reach it, which is determined by the tilt of the earth’s axis. There are generally four seasons: spring, summer, autumn, and winter, corresponding to the dates of solstices and equinoxes.
The Torrid Zone, stretching between 23½° N and S latitudes, more or less receives the vertical rays of the sun. The Temperate Zones and the Frigid Zones receive slanting (oblique or extremely oblique) rays of the sun.
22. How is the duration of twilight influenced by seasons?
Answer: The duration of twilight is influenced by seasons particularly in polar regions. At the poles, the duration of twilight is 50 days long during the 3 months of alternating period of day and night, which is a seasonal phenomenon. For instance, in polar regions, twilight can last for as much as seven weeks at a stretch during the transition between continuous daylight and continuous darkness. During the winter darkness at the poles, what is experienced is often a long period of twilight.
23. How has the phenomenon of the ‘Midnight Sun’ come about?
Answer: The phenomenon of the ‘Midnight Sun’ has come about due to the tilt of the Earth’s axis. On 21st June, when the North Pole is tilted towards the sun, the rays of the sun fall vertically on the Tropic of Cancer. This causes the duration of sunlight to increase towards the North Pole, and beyond the Arctic Circle (at 66½° N), regions experience 24 hours of daylight. This phenomenon is termed as ‘midnight sun’.
24. Mention one effect of seasons in low and high latitudes.
Answer: One effect of seasons is that in low latitudes, such as near the Equator, there are minimal seasonal contrasts, with regions experiencing a moderately warm climate throughout the year and little variation in day length. In high latitudes, such as near the Poles, seasons cause great contrasts, including extreme variations in day length like 24-hour daylight (Midnight Sun) in summer or 24-hour darkness in winter, and very long periods of twilight.
25. Draw a well labelled diagram to show changes in the altitude of the midday sun at different times of the year.
Answer: See Figure 3.4 of the chapter (Total Geography by Morning Star) or click here
Distinguish between the following
(i) Rotation and Revolution.
Answer: Rotation is the spinning of the earth on its axis from west to east once in 24 hours. The earth completes one rotation from west to east on its axis in 23 hours, 56 minutes, 4.09 seconds (roughly in 24 hours). The earth is always tilted in the same direction (towards the Pole Star) as it moves round the sun, and the speed of earth’s rotation at the Equator is 1670 km per hour, decreasing towards the poles.
Revolution is the motion where the earth revolves round the sun in an elliptical orbit. The earth moves round the sun in an elliptical orbit at an average speed of 29.8 kilometres per second or about 100,000 kilometres per hour. When the earth is closer to the sun, the gravitational pull makes the earth move faster than when it is away from the sun, so the speed of revolution is not uniform. The period taken by the earth to make one complete round of the sun is 365 days, 5 hours, 48 minutes and 45.51 seconds, which is taken as 365 days and 6 hours. The earth’s axis is always inclined to its orbital plane at an angle of 66½°, and the motion of the earth is from west to east or in the same direction as the rotation.
(ii) Vertical and Slanting Rays.
Answer: When a place receives vertical sun rays, the place gets hot. This is because the amount of heat in the direct vertical rays is concentrated on a small area. The Torrid Zone, which stretches between 23½° N and S latitudes, more or less receives the vertical rays of the sun.
In the case of slanting or oblique rays, the same amount of heat is spread over a larger area. In the Temperate Zone, between 23½° North and South and 66½° North and South, the sun’s rays fall obliquely. In the Frigid Zone, from 66½° N to 90° N and 66½° S to 90° S, the sun’s rays fall extremely obliquely. The difference in the amount of heat received at different parts of the earth during the year, which depends on the inclination of the sun’s rays, is best explained by vertical and slanting rays of the sun.
(iii) Equinox and Solstice.
Answer: The distinctions between Solstice and Equinox are as follows:
| Solstice | Equinox |
| Solstice refers to the time when the sun reaches its highest or lowest point in the sky at noon, resulting in the shortest and longest days of the year. | Equinox refers to time when the sun crosses the plane of the earth’s Equator, making night and day of equal length. |
| The word Solstice is derived from the Latin words ‘Sol’ meaning ‘sun’ and ‘sistere’ meaning ‘to stand still’. | The word Equinox is derived from the Latin words ‘aequus’ meaning ‘equal’ and ‘nox’ meaning ‘night’. |
| It happens twice a year on June 21 (summer solstice) and December 22 (winter solstice). | It happens twice a year, around March 21 (Spring or Vernal Equinox) and September 23 (Autumnal Equinox). |
| It happens during summer and winter. | It happens at the start of spring and autumn. |
On June 21, the earth is in the position where the North Pole is tilted towards the sun, and the sun is overhead at the Tropic of Cancer; this day is known as the Summer Solstice. On December 22, the Southern Hemisphere is tilted towards the sun, while the Northern Hemisphere is tilted away from the sun; this day is known as the Winter Solstice.
On two days in a year, 21st March (Spring or Vernal Equinox) and 23rd September (Autumnal Equinox), the sun shines vertically over the Equator i.e., at an angle of 90°. At the Equinoxes the days and nights are of equal length throughout the world.
Structured Questions
1. (a) What is meant by rotation of the earth? State three effects of the rotation of the earth.
Answer: Rotation is the spinning of the earth on its axis from west to east once in 24 hours. Three effects of the rotation of the earth are:
(i) Occurrence of Day and Night are caused by the rotation of the earth on its axis.
(ii) Sunrise and Sunset are caused by the rotation of the earth from west to east.
(iii) Coriolis Effect refers to the force experienced by any object moving over the surface of a rotating body such as the earth. The Coriolis Effect plays an important role in the movement of air (winds) and water (ocean currents) on the earth.
(b) What is the effect of the inclined axis of the earth on day and night?
Answer: The effect of the inclined axis on the duration of day and night is that their duration differs. The duration of day and night is not equal at all places on the earth because of the inclined axis. For example, at the Equator, the length of day is equal to the length of night. On the Tropic of Cancer, during certain times of the year, days are longer than nights. On the Arctic Circle, there can be a day of 24 hours near the North Pole in summer, while on the Antarctic Circle, there can be a night for 24 hours near the South Pole in winter.
(c) Give a geographical reason for each of the following:
(i) Kuala Lumpur rotates faster on the earth’s axis than London.
Answer: The speed of earth’s rotation at the Equator is 1670 km per hour. The speed decreases towards the poles. Kuala Lumpur is situated closer to the Equator than London, and therefore, it rotates faster on the earth’s axis.
(ii) We always see the sun rising in the east.
Answer: The earth completes one rotation from west to east on its axis. Because the earth spins from west to east, the sun, the moon and the stars seem to move from east to west. The part of the earth that moves from darkness into the sun’s rays experiences sunrise, and this apparent movement makes us see the sun rising in the east.
(iii) Norway is called the Land of the Midnight Sun.
Answer: On June 21st, it is summer solstice in the Northern Hemisphere. Beyond the Arctic Circle, the regions experience 24 hours daylight. This phenomena is termed as ‘midnight sun’. Norway is called land of midnight sun because, during this time, the sun is visible only at very low height, just above the horizon, even at midnight.
(d) Draw a well labelled diagram to show inclination of the earth on its axis.
Answer: See Figure 3.1 of the chapter (Total Geography by Morning Star) or click here.
2. (a) Describe how the duration of sunlight changes from the Equator to the Poles with respect to the angle of incidence during the solstices.
Answer: During the solstices, the duration of sunlight changes significantly from the Equator to the Poles, and this is related to the angle of incidence of the sun’s rays. Hours of daylight are always 12 hours at the Equator.
On June 21st (summer solstice in the Northern Hemisphere) the duration of sunlight or day time increases from 12 hours at the Equator to 13 hours and 27 minutes at 23½° N (Tropic of Cancer), where the angle of incidence is 90°. It further increases to 24 hours at 66½° N (Arctic Circle), where the angle of incidence is 47°. At the North Pole (90°N), there are 24 hours of daylight with an angle of incidence of 23°30′.
Conversely, in the Southern Hemisphere on this date, the duration of daylight decreases towards the South Pole, reaching 0 hours beyond the Antarctic Circle.
On December 22nd (winter solstice in the Northern Hemisphere, summer in Southern Hemisphere):
The situation is reversed. At the Equator, daylight is 12 hours with an angle of incidence of 63°30′. In the Northern Hemisphere, the duration of sunlight decreases towards the North Pole. For example, at 23°30’N, daylight is 10h 33m with an angle of incidence of 43°. At 66°30’N, there are 0 hours of daylight with an angle of incidence of 0°, and the same at the North Pole.
In the Southern Hemisphere on December 22nd, areas beyond the Antarctic Circle experience 24 hours daylight. For instance, at 90°S (South Pole), there are 24 hours of daylight with an angle of incidence of 23°30′.
Generally, the hours of daylight go on increasing or decreasing towards the Poles from the Equator during solstices.
(b) Describe how seasons are made and reversed between the Northern and Southern Hemispheres.
Answer: Seasons are made due to the tilt of the earth’s axis and its revolution around the sun. The earth’s axis is not perpendicular to the plane of its orbit but is tilted at an angle of 66½° to it, or 23½° from the perpendicular. As a result of this tilt, in the course of the earth’s movement around the sun, the North Pole remains inclined towards the sun for a part of the year while the South Pole is tilted away from it. This gives rise to summer in the Northern Hemisphere and winter in the Southern Hemisphere. For the remaining part of the year, the situation is reversed: the North Pole is tilted away from the sun, and the South Pole is inclined towards it, causing winter in the Northern Hemisphere and summer in the Southern Hemisphere.
This reversal is evident in the positions of the earth during its revolution:
On June 21st (Summer Solstice), the Northern Hemisphere is tilted towards the sun, experiencing summer, while the Southern Hemisphere is tilted away, experiencing winter.
On September 23rd (Autumnal Equinox), the sun is vertically overhead at the Equator. It is autumn in the Northern Hemisphere and spring in the Southern Hemisphere.
On December 22nd (Winter Solstice), the Southern Hemisphere is tilted towards the sun, experiencing summer, while the Northern Hemisphere is tilted away, experiencing winter.
On March 21st (Spring Equinox), the sun is again vertically overhead at the Equator. It is spring in the Northern Hemisphere and autumn in the Southern Hemisphere.
Thus, revolution causes different seasons, which are the changing weather conditions due to differences in the heating of the earth, and these seasons are reversed between the two hemispheres.
(c) Give a geographical reason for each of the following:
(i) The length of day and night is not equal at all places on the earth.
Answer: The length of day and night is not equal at all places on the earth because of the inclined axis of the earth. If the axis were vertical, the length of day and night would be equal at all places.
(ii) The period of twilight and dawn increases polewards.
Answer: The period of twilight (diffused light between sunset and complete darkness) and dawn (diffused light between sunrise and full daylight) increases polewards because the sun rises and sets in an oblique path in temperate and polar latitudes, as opposed to a more vertical path at the Equator. The twilight continues as long as the sun is 18° below the horizon. Its duration is 1 hour and 12 minutes at the Equator and it goes on increasing towards the Poles. At the poles, the duration is 50 days long during the 3 months of alternating period of day and night because the period during which the refracted light is received is longer. The duration of twilight is large beyond 50° latitude and in polar regions twilight lasts for as much as seven weeks at a stretch.
(iii) 25th of December in New Zealand may be one of the hottest days of the year.
Answer: New Zealand is in the Southern Hemisphere. On December 22nd, the Southern Hemisphere is tilted towards the sun and experiences summer. This day is known as the Winter Solstice in the Northern Hemisphere but is the Summer Solstice for the Southern Hemisphere. Since December 25th is very close to December 22nd, New Zealand experiences summer conditions, making it one of the hottest times of the year there.
(d) Draw a well labelled diagram to show the tilt of the earth’s axis and how the revolution causes seasons and variation in the length of day and night.
Answer: See Figure 3.4 of the chapter (Total Geography by Morning Star) or click here.
Thinking Skills
1. Imagine if the earth stops its rotation on its axis. What would be its impact on the inhabitants of the earth? Give examples to support your answer.
Answer: If the Earth stopped rotating on its axis, the impact on inhabitants would be catastrophic.
Permanent Day and Night: One half of the Earth would be in constant, scorching daylight, while the other half would be in perpetual, freezing darkness.
Example: The side facing the sun would become incredibly hot, possibly boiling away oceans and making it impossible for plants and animals to survive. The dark side would become extremely cold, freezing everything solid.
No Daily Cycle: There would be no sunrise or sunset, and the concept of a “day” as we know it (24 hours) would disappear.
Extreme Temperatures: Without rotation to distribute solar energy, the temperature differences between the light and dark sides would be immense, far beyond what any known life could tolerate.
Example: Plants on the sun-facing side would burn up, and those on the dark side would freeze and die from lack of light for photosynthesis.
Life as we know it would cease: The Earth would become uninhabitable for most, if not all, current life forms.
2. You travel for winter vacation to Australia from India. What type of climate will be there in Australia? Give reasons to support your answer.
Answer: If I travel from India to Australia for a winter vacation (meaning it’s winter in India, which is in the Northern Hemisphere), I would expect a summer climate in Australia.
Reason: Australia is in the Southern Hemisphere. Due to the Earth’s tilt on its axis (23½°), when the Northern Hemisphere is tilted away from the sun (experiencing winter), the Southern Hemisphere is tilted towards the sun (experiencing summer). The seasons are opposite in the two hemispheres. So, India’s winter (e.g., December-January) corresponds to Australia’s summer.
3. On June 21, your uncle who lives in New York experiences summer, whereas your cousin who lives in Jakarta, experiences winter. Give reasons to support your answer.
Answer: This is because of the Earth’s tilt and its revolution around the sun, leading to different seasons in different hemispheres and at different latitudes.
New York (Summer): New York is in the Northern Hemisphere. Around June 21st (Summer Solstice), the Northern Hemisphere is tilted towards the sun. This means it receives more direct sunlight, resulting in longer days and warmer temperatures, hence it experiences summer.
Jakarta (Winter – with a caveat): Jakarta, Indonesia, is in the Southern Hemisphere, though it’s very close to the Equator (around 6° South latitude).
On June 21st, the Southern Hemisphere is tilted away from the sun. This is why it’s technically the “winter” period for the Southern Hemisphere.
Project/Activity
1. With the help of a Power Point Presentation show
(i) change of seasons in the Northern Hemisphere.
(ii) the apparent path of the sun from the Equator to North Pole.
Answer: Do it yourself. Here are the instructions:
- Open PowerPoint and create a title slide with the heading “Rotation and Revolution: Change of Seasons and Path of the Sun”.
- Slide 1: Introduction
- Write one or two short points explaining the earth’s rotation and revolution.
- Mention the tilt of the earth’s axis (23½°).
- Slide 2: Change of Seasons in the Northern Hemisphere
- Draw or insert a labelled diagram showing Earth’s orbit around the sun.
- Highlight four key positions: March 21 (Spring), June 21 (Summer), September 23 (Autumn), December 22 (Winter).
- Briefly describe what season occurs at each date.
- Slide 3: Apparent Path of the Sun
- Use a diagram showing the sun’s apparent movement from the Equator to the Tropic of Cancer (around June 21).
- Explain that this movement causes longer days in the Northern Hemisphere in summer.
- Slide 4: Summary
- Add 3–4 bullet points summarising key facts (e.g. solstices, equinoxes, vertical rays, 24-hour day/night near poles).
2. Draw a diagram to show the winter solstice and answer the following questions.
(i) Name the correct date depicted in your diagram.
(ii) Name the latitude where the sun is shining vertically overhead.
(iii) Name the part of the globe where there is night on this date.
(iv) Name the latitude on which length of the day will be 24 hours.
(v) Give the date when the earth will be directly opposite to the above position.
(vi) What will be the vertical position of the sun on that date?
(vii) What is the effect of the inclination of the earth upon the length of day and night?
(viii) What will be the probable length of day and night on that date?
Answer: Do it yourself. Here are the instructions:
- Draw a circle to represent the Earth.
- Tilt it so the South Pole leans towards the Sun.
- Mark the Tropic of Capricorn (23½° S) and show sun rays hitting it vertically.
- Shade the Northern Hemisphere to show it’s experiencing night.
- Label the Arctic Circle, Tropic of Cancer, Equator, Tropic of Capricorn, and Antarctic Circle.
Then answer these questions using the diagram:
- (i) The correct date is December 22.
- (ii) The sun is shining vertically overhead at the Tropic of Capricorn (23½° S).
- (iii) The Northern Hemisphere (especially beyond the Arctic Circle) is in night.
- (iv) On Antarctic Circle (66½° S), the length of the day is 24 hours.
- (v) The opposite date is June 21.
- (vi) On June 21, the sun is vertically overhead at the Tropic of Cancer (23½° N).
- (vii) Because of the earth’s tilted axis, day and night are not equal at most places. Some places have longer days or longer nights depending on their position and the time of year.
- (viii) On December 22, most places (except the Equator) have unequal day and night. At the Equator it is about 12 hours each; in the far north, it could be almost 24 hours of night.
Extras
Additional MCQs
1. The spinning of the Earth on its axis is known as:
A. Rotation
B. Revolution
C. Orbit
D. Tilt
Answer: A. Rotation
45. The circle dividing the lighted and dark halves of the Earth at any moment is the:
A. Circle of illumination
B. Equator
C. Meridian
D. Tropic
Answer: A. Circle of illumination
Additional Assertion and Reasons
1. Assertion (A): The occurrence of day and night is caused by the Earth’s rotation.
Reason (R): The Earth rotates from East to West on its axis.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (c) A is true but R is false.
31. Assertion (A): The duration of twilight is shortest at the Equator and tends to increase as one moves towards the poles.
Reason (R): At the Equator, the sun’s path during sunrise and sunset is nearly vertical, leading to a rapid transition, whereas at higher latitudes, the sun’s oblique path prolongs the period of refracted and scattered sunlight.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (a) Both A and R are true and R is the correct explanation of A.
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