Seasons

Definition of Seasons

• Seasons refer to periodic climate changes experienced throughout the year.
• The year is divided into four main seasons: Spring, Summer, Autumn, and Winter.
• Seasons occur due to Earth’s axial tilt and revolution around the Sun.

Cause of Seasons (Tilt of Earth’s Axis and Revolution)

• The Earth’s axis is tilted at an angle of 23.5°.
• As Earth revolves around the Sun, different parts receive varying amounts of sunlight.
• This variation in solar intensity leads to seasonal changes.

Solstices and Equinoxes

• Solstice: When the Sun is directly overhead at the Tropics (Cancer/Capricorn).
  • Summer Solstice (21st June): Longest day in the Northern Hemisphere.
  • Winter Solstice (22nd December): Longest night in the Northern Hemisphere.
• Equinox: When the Sun is directly overhead at the Equator.
  • Spring Equinox (21st March) and Autumn Equinox (23rd September).
  • Day and night are equal worldwide.

Summer Season

• Occurs when a hemisphere is tilted toward the Sun.
• More direct sunlight → Longer days, shorter nights.
• In the Northern Hemisphere: June to September.
• In the Southern Hemisphere: December to March.

Winter Season

• Occurs when a hemisphere is tilted away from the Sun.
• Less direct sunlight → Shorter days, longer nights.
• In the Northern Hemisphere: December to March.
• In the Southern Hemisphere: June to September.

Spring Season

• Occurs after winter as the hemisphere starts tilting toward the Sun.
• Moderate temperatures, increasing daylight.
• Spring Equinox marks its beginning.
• In the Northern Hemisphere: March to June.
• In the Southern Hemisphere: September to December.

Autumn Season

• Occurs after summer as the hemisphere starts tilting away from the Sun.
• Gradual cooling, shorter days, and shedding of leaves in temperate zones.
• Autumn Equinox marks its beginning.
• In the Northern Hemisphere: September to December.
• In the Southern Hemisphere: March to June.

Variation in Day and Night Length

• Due to Earth’s tilt, the length of day and night changes throughout the year.
• At Equinoxes, day and night are equal worldwide.
• At Solstices, extreme variations occur:
  • Summer Solstice: Longest day, shortest night.
  • Winter Solstice: Shortest day, longest night.
• At the poles, the Sun remains visible for 6 months (Midnight Sun) and remains dark for 6 months (Polar Night).

Seasons in the Northern Hemisphere

• Spring: March – June (Begins with Spring Equinox).
• Summer: June – September (Begins with Summer Solstice).
• Autumn: September – December (Begins with Autumn Equinox).
• Winter: December – March (Begins with Winter Solstice).

Seasons in the Southern Hemisphere

• Spring: September – December (Begins with Spring Equinox).
• Summer: December – March (Begins with Summer Solstice).
• Autumn: March – June (Begins with Autumn Equinox).
• Winter: June – September (Begins with Winter Solstice).