Seasons

Summary

Seasons are recurring annual changes in temperature and daylight caused mainly by Earth's axial tilt and revolution.

Core concept

Understand the system

Seasons are recurring annual changes in temperature and daylight caused mainly by Earth's axial tilt and revolution.

Why / how it happens

Causes and context

Seasons occur because Earth's axis is tilted about 23.5° and maintains its orientation while Earth revolves around the Sun. The tilt changes both solar altitude and daylight duration, so each hemisphere receives different insolation through the year.

Mechanism / process

First, Earth's tilted axis maintains near-parallel orientation during revolution. Next, the subsolar point migrates between the Tropic of Cancer and Tropic of Capricorn. Then solar altitude and day length change by latitude, producing solstices, equinoxes and opposite hemispheric seasons.

Key facts

• Equinoxes have nearly equal day and night globally.
• Solstices mark maximum seasonal solar declination: about 23.5°N or 23.5°S.
• The Northern and Southern Hemispheres have opposite seasons.

Important terminology

• solstice
• equinox
• solar declination
• insolation
• tropic

Established figures

• Solstices mark maximum seasonal solar declination: about 23.5°N or 23.5°S.

Named examples / case studies

• The June solstice brings the Sun overhead at the Tropic of Cancer.

Causes / components

• Earth's approximately 23.5° axial tilt.
• Earth's annual revolution around the Sun.
• The changing angle and duration of incoming solar radiation.

Effects / significance

• Solstices mark maximum solar declination and seasonal contrast.
• Equinoxes produce nearly equal day and night globally.
• Opposite seasons occur in opposite hemispheres.

Geography connection

The June solstice brings the Sun overhead at the Tropic of Cancer. This illustrates how seasons varies by location, scale or environmental context.

Bangladesh connection

At about 23.5°N, the June solstice is especially relevant to Bangladesh's high summer solar altitude and monsoon context.

BCS preliminary facts

• Equinoxes have nearly equal day and night globally.
• Solstices mark maximum seasonal solar declination: about 23.5°N or 23.5°S.
• The Northern and Southern Hemispheres have opposite seasons.

BCS written analysis

Build an analytical answer

• Show the cause-effect chain from axial tilt to changing insolation, temperature and day length.
• Contrast solstice and equinox conditions using the tropics and polar circles.
• Relate Bangladesh's pre-monsoon and monsoon seasonality to solar geometry without claiming tilt alone causes rainfall.

Common misconceptions

• Seasons are not caused by changing Earth-Sun distance.
• The Equator does not have four temperate seasons like mid-latitudes.

Quick revision

• Seasons
• Equinoxes have nearly equal day and night globally.
• Solstices mark maximum seasonal solar declination: about 23.5°N or 23.5°S.
• solstice / equinox
• Definition → process → spatial example