Notes Class 7 Chapter 8 Geography Maharashtra Board

Notes For All Chapters – Geography Class 7

How Seasons Occur – Part 2

1. Introduction to Seasons

• Seasons occur due to the Earth’s revolution around the Sun and the tilt of its axis.
• Different parts of the Earth receive varying amounts of sunlight throughout the year, leading to seasonal changes.

2. Apparent Movement of the Sun

• The Sun does not actually move, but due to the Earth’s movement, it appears to shift northward or southward over the year.
• This apparent movement causes variations in the position of sunrise and sunset.

Dakshinayan (Southward Movement)

• From 21st June to 22nd December, the Sun appears to move southward.
• The Tropic of Cancer stops receiving direct sunlight, and the days become shorter in the Northern Hemisphere.

Uttarayan (Northward Movement)

• From 22nd December to 21st June, the Sun appears to move northward.
• The Tropic of Capricorn stops receiving direct sunlight, and the days become longer in the Northern Hemisphere.

3. Solstices and Equinoxes

Summer Solstice (21st June)

• The longest day and shortest night in the Northern Hemisphere.
• The shortest day and longest night in the Southern Hemisphere.
• The Tropic of Cancer receives perpendicular sun rays.

Winter Solstice (22nd December)

• The longest day and shortest night in the Southern Hemisphere.
• The shortest day and longest night in the Northern Hemisphere.
• The Tropic of Capricorn receives perpendicular sun rays.

Equinoxes (21st March & 23rd September)

• Equal day and night (12 hours each) all over the world.
• 21st March (Vernal Equinox): Start of spring in the Northern Hemisphere and autumn in the Southern Hemisphere.
• 23rd September (Autumnal Equinox): Start of autumn in the Northern Hemisphere and spring in the Southern Hemisphere.

4. The Earth’s Revolution and Tilt

• The Earth revolves around the Sun in an elliptical orbit.
• The Earth’s axis is tilted at 23.5°, causing different parts of the Earth to receive varying amounts of sunlight throughout the year.
• This leads to the formation of seasons.

5. The Perihelion and Aphelion Positions of the Earth

• The Earth’s orbit is elliptical, meaning its distance from the Sun varies.
• Perihelion (Early January): Earth is closest to the Sun.
• Aphelion (Early July): Earth is farthest from the Sun.
• These do not have a significant effect on the seasons.

6. Seasonal Changes in the Northern & Southern Hemispheres

• The Northern Hemisphere experiences summer from March to September and winter from September to March.
• The Southern Hemisphere experiences opposite seasons-summer from September to March and winter from March to September.

7. Effect of Seasons on Day & Night Duration

• In the polar regions, the Sun remains visible for 24 hours for several months.
• Midnight Sun: In places like Norway, the Sun remains visible for six months during summer.
• Six-Month Night: At the South Pole, the Sun is not visible for six months during winter.

8. Why the Equatorial Region Does Not Experience Seasons?

• The equator receives almost equal sunlight throughout the year.
• There is no significant difference in temperatures or day-night durations.
• Thus, the equatorial region does not have distinct seasons.

9. Impact of the Cycle of Seasons on Living Beings

• The tilt of the Earth’s axis creates a diverse climate, leading to different ecosystems and adaptations.
• In the Arctic and Antarctic, animals like penguins, walruses, and polar bears have adapted to extreme cold.
• In tropical regions, plants and animals are adapted to constant warmth and humidity.
• Bird Migration: Birds like the Arctic Tern migrate thousands of kilometers to experience summer twice a year.

10. Importance of the Seasons in Human Life

• Agriculture depends on seasonal changes, affecting crop growth and harvest cycles.
• Festivals and cultural events are often linked to specific seasons.
• Tourism and sports activities are influenced by the weather conditions of different regions.

Conclusion

• The revolution of the Earth and the tilt of its axis cause seasonal variations.
• The cycle of seasons impacts climate, biodiversity, and human activities.
• The solstices and equinoxes mark important changes in day length and temperature.