Notes Class 7 Chapter 1 Geography Maharashtra Board

Notes For All Chapters – Geography Class 7

How Seasons Occur – Part 1

Introduction

• The Earth moves continuously in space, which causes different natural phenomena such as day and night and seasonal changes.
• This chapter focuses on the Earth’s rotation and revolution and how they affect the duration of day and night throughout the year.
• We will also understand the changing positions of sunrise and sunset and how this influences seasons.

1. How Day and Night Occur

1.1 Earth’s Rotation

• The Earth rotates around its own axis.
• The axis is an imaginary line passing through the North Pole and South Pole.
• The Earth rotates from west to east and takes 24 hours to complete one full rotation.
• This rotation is responsible for the occurrence of day and night.

1.2 How Does Rotation Cause Day and Night?

• The part of the Earth facing the Sun experiences daytime, while the part facing away from the Sun has nighttime.
• This cycle repeats every 24 hours, creating a daily pattern of sunrise and sunset.
• The rotation of the Earth helps in measuring time in terms of days.

2. Changes in the Duration of Day and Night

2.1 Why Don’t Day and Night Have Equal Duration?

• The duration of day and night is not the same throughout the year.
• This happens because of:
  1. Earth’s axial tilt (23.5°).
  2. Earth’s revolution around the Sun.

2.2 Observing Changes in Day and Night Duration

• The duration of day and night gradually changes throughout the year.
• In summer, days are longer and nights are shorter.
• In winter, days are shorter and nights are longer.
• The difference in day and night duration is greater near the poles and smaller near the equator.

3. Earth’s Revolution Around the Sun

3.1 What is Revolution?

• The Earth moves around the Sun in an elliptical (oval-shaped) orbit.
• This movement is called revolution.
• The Earth takes 365¼ days (one year) to complete one full revolution around the Sun.

3.2 The Tilt of the Earth’s Axis

• The Earth’s axis is tilted at an angle of 23.5°.
• This tilt remains fixed in the same direction as the Earth moves around the Sun.
• Due to this tilt, different parts of the Earth receive varying amounts of sunlight at different times of the year, leading to seasonal changes.

4. Changing Position of Sunrise and Sunset

4.1 Why Does the Position of the Sun Change?

• The position of sunrise and sunset does not remain the same throughout the year.
• As the Earth revolves around the Sun, the position of the Sun appears to shift northward or southward in the sky.
• This change affects the duration of daylight hours.

4.2 Observing Changes in Sunrise and Sunset

• The Sun appears to rise in the east and set in the west every day.
• However, its exact position on the horizon changes slightly throughout the year.
• In summer, the Sun rises early and sets late, making the days longer.
• In winter, the Sun rises late and sets early, making the days shorter.

4.3 Seasonal Changes Due to Sun’s Position

• The Sun appears to move towards the north from January to June (Summer Solstice).
• The Sun appears to move towards the south from July to December (Winter Solstice).
• This movement causes seasonal variations in different parts of the Earth.

5. Activities to Understand Day and Night Changes

5.1 Observing Day and Night Duration

• Record the sunrise and sunset timings for a few days in a month.
• Compare the length of the day and night using a table.
• Identify the longest and shortest days of the year.

5.2 Shadow Experiment

• Take a stick or rod and place it in the sunlight.
• Observe the direction and length of its shadow at different times of the day.
• Compare shadows in summer and winter to see the change in the Sun’s position.

6. Important Terms to Remember

7. Summary of Key Learnings

• The Earth rotates on its axis, causing day and night.
• The Earth revolves around the Sun, leading to seasonal changes.
• The duration of day and night changes throughout the year due to the tilt of the Earth’s axis.
• The position of sunrise and sunset shifts slightly due to Earth’s revolution.
• Observing shadows, sunrise, and sunset times helps in understanding these changes.

Conclusion

• The Earth’s movements (rotation and revolution) are responsible for the occurrence of day and night and changing seasons.
• The tilt of the Earth’s axis plays a crucial role in varying the duration of daylight hours.
• By observing natural changes, such as sunrise, sunset, and shadows, we can understand these geographical phenomena better.