Change of Seasons – Complete Detailed Notes for Competitive Examination
By Home Academy
Introduction
The change of seasons refers to the periodic variation in weather conditions during the year due to the movement of Earth around the Sun and the inclination of Earth’s axis.
Seasonal change affects temperature, rainfall, day length, agriculture, climate, vegetation, animal life, and human activities.
What is a Season?
A season is a division of the year characterized by specific weather patterns and daylight hours.
Earth generally experiences four main seasons:
Spring
Summer
Autumn (Fall)
Winter
However, in tropical countries like India, seasons are commonly divided into:
Winter Season
Summer Season
Rainy (Monsoon) Season
Retreating/Post-Monsoon Season
Main Causes of Change of Seasons
The change of seasons occurs mainly because of three factors:
1. Revolution of Earth
Earth revolves around the Sun in an elliptical orbit.
Time taken for one revolution:
365¼ days (1 year)
As Earth moves around the Sun, different parts receive different amounts of sunlight.
2. Inclination of Earth’s Axis
Earth’s axis is tilted at 66½° to the plane of orbit or 23½° from vertical.
This tilt is the most important reason for seasonal change.
If Earth had no tilt, seasons would not exist.
3. Parallelism of Earth’s Axis
During revolution, Earth’s axis remains parallel in one direction.
Because of this, different hemispheres receive varying solar energy.
Why Seasons Change?
Earth receives sunlight at different angles.
Direct rays → More heat
Slanting rays → Less heat
When one hemisphere receives direct sunlight:
→ Summer there
→ Winter in opposite hemisphere
Solstices and Equinoxes
These are important positions of Earth during revolution.
1. Summer Solstice
Date: 21 June
Sun’s vertical rays fall on Tropic of Cancer (23½° N).
Effects:
• Northern Hemisphere → Summer
• Southern Hemisphere → Winter
• Longest day in Northern Hemisphere
• Shortest night in Northern Hemisphere
Important fact:
Arctic region experiences Midnight Sun.
2. Winter Solstice
Date: 22 December
Sun’s vertical rays fall on Tropic of Capricorn (23½° S).
Effects:
• Southern Hemisphere → Summer
• Northern Hemisphere → Winter
• Shortest day in Northern Hemisphere
• Longest night in Northern Hemisphere
3. Vernal (Spring) Equinox
Date: 21 March
Sun shines directly on Equator.
Effects:
• Day and night equal worldwide
• Spring begins in Northern Hemisphere
• Autumn begins in Southern Hemisphere
4. Autumnal Equinox
Date: 23 September
Sun’s rays fall directly on Equator.
Effects:
• Equal day and night
• Autumn begins in Northern Hemisphere
• Spring begins in Southern Hemisphere
Seasonal Distribution in Northern Hemisphere
| Season | Approx. Months |
|---|---|
| Spring | March–May |
| Summer | June–August |
| Autumn | September–November |
| Winter | December–February |
Seasonal Distribution in Southern Hemisphere
| Season | Approx. Months |
|---|---|
| Spring | September–November |
| Summer | December–February |
| Autumn | March–May |
| Winter | June–August |
Effect of Seasons on Climate
Summer
Temperature increases.
Characteristics:
• Long days
• Short nights
• More evaporation
• Agricultural growth
Winter
Temperature decreases.
Characteristics:
• Short days
• Long nights
• Snowfall in cold regions
Spring
Moderate temperature.
Characteristics:
• Flower blooming
• New vegetation
Autumn
Transition season.
Characteristics:
• Leaves fall
• Cooling starts
Change of Seasons in India
India mainly experiences four seasons.
Winter Season (December–February)
Characteristics:
• Low temperature
• Western disturbances bring rain in North India
Summer Season (March–May)
Characteristics:
• High temperature
• Formation of low pressure
Southwest Monsoon Season (June–September)
Characteristics:
• Heavy rainfall
• Agriculture dependent on monsoon
Retreating Monsoon (October–November)
Characteristics:
• Withdrawal of monsoon
• Rain in Tamil Nadu region
Important Terms
Insolation
Incoming solar radiation received by Earth.
Greater insolation → Higher temperature.
Equinox
Equal day and equal night.
Occurs twice:
21 March
23 September
Solstice
Longest or shortest day.
Occurs twice:
21 June
22 December
Perihelion
Earth closest to Sun.
Occurs around 3 January
Aphelion
Earth farthest from Sun.
Occurs around 4 July
Important: Distance from Sun is not the main cause of seasons.
Importance of Seasonal Change
Supports agriculture
Maintains ecosystems
Controls rainfall distribution
Influences biodiversity
Regulates water cycle
Supports food production
Important Examination Facts
Earth rotates west to east.
Revolution causes year formation.
Earth takes 365¼ days around Sun.
Earth’s tilt = 23½°.
Equinox means equal day and night.
Solstice means maximum seasonal difference.
Tropic of Cancer receives vertical rays on 21 June.
Tropic of Capricorn receives vertical rays on 22 December.
Seasons are opposite in both hemispheres.
Earth’s distance from Sun is not responsible for seasons.
MCQ Questions (Single Correct)
Q1. Main cause of seasons is:
A. Rotation
B. Revolution and tilt
C. Winds
D. Moon
Answer: B
Q2. Sun shines vertically over Tropic of Cancer on:
A. 22 December
B. 21 June
C. 23 September
D. 21 March
Answer: B
Q3. Equal day and night occur during:
A. Solstice
B. Equinox
C. Eclipse
D. Rotation
Answer: B
Q4. Earth completes revolution in:
A. 365¼ days
B. 300 days
C. 400 days
D. 250 days
Answer: A
Q5. Which season occurs in Northern Hemisphere in December?
A. Spring
B. Summer
C. Winter
D. Autumn
Answer: C
Statement Type Questions (More Than One Correct)
Q1. Consider the statements:
Earth’s axis is tilted.
Revolution causes seasonal variation.
Equinox means equal day and night.
Seasons occur due to Earth–Moon distance.
Options:
A. 1, 2 and 3 only
B. 2 and 4 only
C. 1 and 4 only
D. All correct
Answer: A
Q2. Which statements are correct?
Summer Solstice occurs on 21 June.
Winter Solstice occurs on 22 December.
Seasons are same in both hemispheres.
Distance from Sun is main reason for seasons.
Options:
A. 1 and 2 only
B. 1, 2 and 3 only
C. 2 and 4 only
D. All correct
Answer: A
Seasons = Revolution + Axis Tilt + Parallelism
21 March → Equinox
21 June → Summer Solstice
23 September → Equinox
22 December → Winter Solstice