Movements of the Earth: Rotation and Revolution Class 8 Notes Questions and Answers Social Science Chapter 3

By reviewing Kerala Syllabus 8th Standard Social Science Notes Pdf and Class 8 Social Science Chapter 3 Movements of the Earth: Rotation and Revolution Notes Questions and Answers Kerala SCERT Solutions, students can improve their conceptual understanding.

Class 8 Social Science Chapter 3 Movements of the Earth: Rotation and Revolution Notes Questions and Answers

Class 8 Social Science Movements of the Earth: Rotation and Revolution Notes Questions and Answers

Class 8 Social Science Chapter 3 Question Answer Kerala Syllabus

Question 1.
Look at the given figure and answer the following questions related to rotation.

Answer:

Direction of the Earth’s rotation	West to East
Tilt of the Earth’s axis	23 1/2°

Question 2.
Some facts related to rotation are given below. Complete the table by finding out the reasons behind these facts.
Answer:

The sun rises in the east and sets in the west.	The direction of rotation of the Earth is from west to east.
Freely moving bodies get deflected in their direction in both hemispheres.	Coriolis effect.

Question 3.
Have you identified 2024 as a leap year from the given calendar?
Find out five consecutive leap years after 2024.

Answer:
The next five leap years after 2024 are: 2028, 2032, 2036, 2040, 2044.

Question 4.
Observe the picture and find answers

a. On which latitude do the Sun’s rays fall vertically?
b. On which days does this happen?
Answer:
a. Equator
b. 21^st March and 23^rd September

Question 5.
Find out the duration of daytime at your place on 21st March and 23rd September based on the time of sunrise and sunset given in the calendar.
Answer:
Duration of daytime in march 21^st is 12 hours and in September 23^rd is 12 hours.

Question 6.
a. In which direction does the apparent position of the sun shift from 21st March onwards?
b. On which latitude do the sun’s rays fall vertically on 21st June?

Answer:
a. From March 21st, the relative position of the Sun in the Northern Hemisphere moves towards the northern line.
b. On June 21st, the Sun’s rays fall vertically directly above the northern line.

Question 7.
The table showing the length of day in different latitudes on the summer solstice (June 21) is given below.

Latitude	Length of the day
90° North	24 hours
66 1/2° North	24 hours
23 1/2° North	13 hours 27 minutes
0°	12 hours
23 1/2° South	10 hours 33 minutes
66 1/2° South	Nil
90° South	Nil

What are the changes that happen to the length of day in the southern hemisphere on the summer solstice (June 21)?
Answer:
On the summer solstice (June 21), the Southern Hemisphere is tilted away from the Sun. As a result, the length of the day decreases as we move from the equator towards the South Pole. At 23 1/2° South, the day is shorter than 12 hours (10 hours 33 minutes), and it continues to decrease. At 66 1/2° South and 90° South, there is no daylight at all (0 hours), meaning these areas experience polar night.

Question 8.
What will be the duration of the night in the southern polar regions when there is daylight for six months in the northern polar regions?
Answer:
The southern polar regions experience continuous darkness. Therefore, the duration of the night in the southern polar regions during this period is six months.

Question 9.
a. In which direction does the Sun’s apparent position shift from 23rd September onwards?
b. On which latitude do the Sun’s rays fall vertically on 22nd December?

Answer:
a. The Sun’s apparent position shifts from the equator to the Tropic of Capricorn during the period from 23rd September to 22nd December. As
b. On December 22, the sun’s rays fall vertically directly above the southern hemisphere.

Question 10.
The table shows the duration of daytime in different latitudes on the winter solstice (December 22). What are the changes that happen to the length of the day in the northern hemisphere on the Winter Solstice (December 22)?

Latitude	Length of the day
90° North	Nil
66 1/2° North	Nil
23 1/2° North	10 hours 33 minutes
0°	12 hours
23 1/2°  South	13 hours 27 minutes
66 1/2°  South	24 hours
90° South	24 hours

Answer:
On December 22 (Winter Solstice), the Northern Hemisphere has its shortest day.

Question 11.
Complete the table.

Answer:

Question 12.
Observe the table about the different seasons in northern and southern hemispheres and write the answers for the questions given below.

a. What change happens to the apparent movement of the Sun when it is summer season in the northern hemisphere?
b. What will the season be in the northern hemisphere when it is autumn in the southern hemisphere?
c. Which season is experienced in the southern hemisphere from 23rd September to 22nd December?
d. Name the season in the southern hemisphere when the Sun’s apparent position shifts from the Tropic of Capricorn to the equator.
Answer:
a. From the Tropic of Cancer to the Equator
b. Spring
c. Spring
d. Summer

Question 13.
What will be the time at 1° East and 1° West when it is 10:00 A.M. at Greenwich Meridian (0° longitude)?

Answer:

Question 14.
When it is 9.00 P.M. at Greenwich Meridian (0° longitude) what will (he time be at 30° East?

Answer:

Question 15.
What is the time difference between Greenwich Meridian (0° longitude) and Indian Standard Meridian (82 1/2° East)?
Answer:
The Indian Standard Meridian is at 82 1/2° East of the Greenwich Meridian (0°).
Since the Earth rotates 15° per hour, each 1° = 4 minutes of time.
Time difference = 82 1/2° × 4
= 330 Minutes
= 330/ 60
= 5 hours 30 minutes

Question 16.
In Figure given below what is the time and date at 180° East and 180° West when it is December 25 evening 6 p.m. at Greenwich Meridian?

Answer:

• At 180° East: 180° × 4 minutes =12 hours ahead of GMT
  So, 6:00 p.m. + 12 hours = 6:00 a.m., December 26
• At 180° West: 180° × 4 minutes = 12 hours behind GMT
  So, 6:00 p.m. – 12 hours = 6:00 a.m.. December 25

Class 8 Movements of the Earth: Rotation and Revolution Questions and Answers Extended Activities

Question 1.
Observe the changes in nature during the different seasons in your locality and note down the same in the Social Science Observation Book.
Answer:
(Hints)

Seasons	Changes
Spring	• The weather is pleasant. • Flowers bloom everywhere. • Trees grow new green leaves. • Birds are active and chirping.
Summer	• Days are hot and sunny. • People wear light cotton clothes. • Water levels go down. • Fans and coolers are used more.
Autumn	• Leaves change colour and fall from trees. • The weather becomes cooler. • The sky is usually clear. • Fields are harvested in many areas.
Winter	• Days are cold, nights are colder. • People wear sweaters and jackets. • Mornings may be foggy. • Trees may look bare.

Question 2.
Calculate the time duration of day and night in your place on 22nd December and 21st June based on the time of sunrise and sunset.
Answer:
In our area, on December 22, sunrise is at 6:43 am and sunset is at 6:06 pm. The length of the day is 11 hours and 23 minutes. On June 21, sunrise is at 6:08 am and sunset is at 6:45 pm. The length of the day is 12 hours and 37 minutes.

Movements of the Earth: Rotation and Revolution Class 8 Notes Pdf

Std 8 Social Science Movements of the Earth: Rotation and Revolution Notes

• Rotation is the spinning of the Earth on its imaginary axis.
• The direction of rotation of the Earth is from the west to the east.
• The sun rises in the east and sets in the west.
• The time taken for the Earth to complete one rotation is 24 hours (23 hours 56 minutes 4 seconds).
• While rotating on its axis, the Earth revolves around the Sun in a fixed orbit. This is known as Revolution.
• The time taken to complete one revolution in the elliptical orbit is 365 days.
• 365 days is considered as one year for practical convenience.
• The tilt of the Earth’s axis is maintained at an angle of 23 1/2° throughout the revolution, and the Sun’s apparent position moves northward and southward between the Tropic of Cancer and the Tropic of Capricorn.
• 21st March is known as Spring Equinox and 23rd September is Autumnal Equinox.
• Similar to the Earth and the Moon, the Sun also has two movements – rotation and revolution.
• Due to the apparent shift in the position of the Sun, different places experience specific weather patterns. These patterns are known as seasons.
• The revolution of the Earth and variations in the availability of solar energy are the reasons for the occurrence of the seasons.
• The Earth takes 24 hours to complete one rotation or to spin 360° on its axis. This is the time taken to complete one rotation.
• The time calculated based on the length of the shadow and position of the Sun is termed as the Local time.
• Time worldwide is calculated based on GMT.

INTRODUCTION

This chapter, “Movements of the Earth: Rotation and Revolution”, helps us to understand how the movements of the Earth affect our daily life. The Earth rotates on its axis, causing day and night. It also revolves around the Sun, leading to the change of seasons like summer, winter, spring, and autumn. Due to these movements, the Sun appears to move across the sky. This phenomenon is known as the apparent movement of the Sun. These movements help us measure time, and since different places on Earth experience different times, the world is divided into time zones. By learning about rotation, revolution, and their impact on seasons and time, we can gain a deeper understanding of the world around us.

ROTATION

• Rotation is the spinning of the Earth on its imaginary axis.
• The direction of rotation of the Earth is from the west to the east.
• The sun rises in the east and sets in the west.

DAY AND NIGHT

• The time taken for the Earth to complete one rotation is 24 hours (23 hours 56 minutes 4 seconds).
• The Earth receives light from the Sun.
• During rotation, the part of the Earth facing the Sun has daytime and the other part experiences night.
• The imaginary line that demarcates day and night on the Earth is called the Circle of Illumination.
• This circle of illumination is not parallel to the Earth’s Axis.

Mars & Uranus The direction of rotation of all planets except the Mars and the Uranus is from the west to the east. The direction of rotation of Mars and Uranus is in the opposite direction, that is, from the east to the west.

CORIOLIS EFFECT

REVOLUTION

• While rotating on its axis, the Earth revolves around the Sun in a fixed orbit. This is known as Revolution.
• The time taken to complete one revolution in the elliptical orbit is 365 days.
• 365 days is considered as one year for practical convenience.
• The fraction of 14 days is added once in 4 years to February, making it 29 days. Thus, the year that has 366 days is called a leap year.

PERIHELION AND APHELION

• Since the Earth’s orbit is elliptical, there is a difference in the distance between the Earth and the Sun.
• The day on which the Earth comes closest to the Sun during revolution (147 million kilometres) is known as Perihelion.
• This happens in the month of January (around 3rd January). The distance between the Sun and the Earth will be at a maximum (152 million kilometres) in the month of July (around 4th July). This is called Aphelion.
• The speed of revolution of the Earth is around 30 km per second. The distance between the Earth and the Sun causes a difference in gravitational force and the speed of revolution.

Precession
Precession is another movement of the Earth, like rotation and revolution. This is the axial rotation of the Earth. As given in the picture, when the Earth takes twenty-four hours to complete one rotation, it takes around 26000 years for the Earth’s axis to complete one circle slowly.

APPARENT MOVEMENT OF THE SUN

• The tilt of the Earth’s axis is maintained at an angle of 23 1/2° throughout the revolution, and the Sun’s apparent position moves northward and southward between the Tropic of Cancer and the Tropic of Capricorn.
• This apparent shift in the Sun’s position is called the apparent movement of the Sun.

EQUINOX

• During the Revolution, on 21st March and 23rd September, the sun’s rays fall vertically on the equator.
• The duration of day and night will be equal on both hemispheres on these days.
• These days are called equinoxes. 21st March is known as Spring Equinox and 23rd September is Autumnal Equinox.

SUMMER SOLSTICS

Movements of the Sun Similar to the Earth and the Moon, the Sun also has two movements- rotation and revolution. The Sun completes its rotation on its axis in 27 days. It takes around 230 to 250 million years for the solar system, including the sun, to revolve around the centre of the Galaxy, called the Milky Way.

WINTER SOLSTICS

Aurora Aurora is seen in the polar regions during winter months when strong solar winds are experienced. Aurora is the natural coloured light in the atmosphere at high latitudes. It is called Arora Borealis in the Northern Polar region and Aurora Australis in the Southern polar region.

• Following the winter solstice (December 22), the apparent movement of the Sun from Tropic of Capricorn (23/1/2° South) to Tropic of Cancer (23/1/2° North) is known as the apparent movement of the Sun towards the North (Uttarayanam).
• The shift in the apparent position of the Sun after the Summer Solstice (June 21) from the Tropic of Cancer (23 1/2° North) to Tropic of Capricorn (23/1/2° South) is known as the apparent movement of the Sun towards South (Dakshinayanam).

SEASONS

• Due to the apparent shift in the position of the Sun, different places experience specific weather patterns. These patterns are known as seasons.
• The revolution of the Earth and variations in the availability of solar energy is the reason for the occurrence of the seasons.
• The occurrence of spring, summer, autumn and winter in a cyclical manner during a year is called seasonal change.

Different seasons and their Characteristics

Spring	• Plants bloom and produce fruits. • During this period duration of daytime gradually increases.
Summer	• High atmospheric temperature • Generally longer days
Autumn	• Trees shed their leaves before the arrival of winter. • During this period duration of daytime gradually decreases.
Winter	• low atmospheric temperature • SnowfallGenerally longer nights

TIME

• The Earth takes 24 hours to complete one rotation or to spin 360° on its axis.
• This is the time taken to complete one rotation.
  • If it takes 1 hour to turn 15°, how much time will it take to turn 1°?
    15° = 1 hour = 60 minutes
    1° = \(\frac{60}{15}\) = 4 minutes
    The proportionate time difference for 1° longitudinal extent is 4 minutes.

LOCAL TIME

• In the early days, local time was calculated based on the shadow and the overhead position of the Sun.
• It was considered to be noon when the Sun is vertically overhead. Length of the shadow is the shortest at this time.
• Thus, the time calculated based on the length of the shadow and position of the Sun is termed as the Local time.

STANDARD TIME

GREENWICH MEAN TIME

• Circles of latitude decrease in size from equator to poles, but all longitudes are equal semi-circles.
• The Prime Meridian (0° meridian) passes through the Royal Observatory, Greenwich (England).
• The local time at the Prime Meridian is called Greenwich Mean Time (GMT).
• Time worldwide is calculated based on GMT.
• As Earth rotates west to east, time adds 4 minutes per degree east and subtracts 4 minutes per degree west of Greenwich.

INDIAN STANDARD TIME

• There’s a 30° longitudinal difference between Arunachal Pradesh (97°.25’ East) and Gujarat (68°.7’ East).
• This creates a 2-hour local time difference between the two ends of India.
• To avoid confusion, a Standard Time is set for the whole country.
• The 82 1/2° East longitude is chosen as the Standard Meridian of India.
• The local time at this meridian is called the Indian Standard Time (IST).

TIME ZONES

• Based on international understanding, the world has been divided into 24 zones with 1 hour difference. These are time zones. Each time zone has 15° longitudinal distance.
• Countries like Russia, the U.S.A., and Australia, with large longitudinal extensions, have many time
  Zones and standard time.

INTERNATIONAL DATE LINE

• 180° East and 180° West refer to the same longitude.
• There’s a 24-hour time difference across this line.
• Eastward travellers lose a day, while westward travellers gain a day.
• This line is called the International Date Line (IDL).
• Based on global agreement, IDL marks the change of calendar date.
• To avoid two dates in one country, the line is adjusted to skip populated areas in the Pacific Ocean.
• Earth’s rotation and revolution affect time, seasons, and daily life.
• These changes impact the social and cultural life of people worldwide.