Seasons and Earth's Tilt

Overview

This lecture explains why seasons occur and why summer is hot and winter is cold, focusing on the Earth's tilt and the effects of sunlight angle and duration.

Why Seasons Happen

Seasons are not caused by Earth's distance from the Sun.
The Earth's axis tilt causes different parts of Earth to lean toward or away from the Sun during its orbit.

Reason 1: Length of Daylight

In summer, days are longer because your location is tilted toward the Sun.
In winter, days are shorter because your location is tilted away from the Sun.
Longer daylight in summer allows more time for the Sun to heat the ground.

Reason 2: Angle of Sunlight

In summer, the Sun appears higher in the sky and sunlight strikes the ground more directly.
Direct sunlight in summer is concentrated, heating the ground more efficiently.
In winter, the Sun is lower in the sky and sunlight arrives at a shallow angle.

Effects of Sunlight Angle

Shallow sunlight in winter spreads over a larger area, reducing heat per unit of ground.
Spread-out light gives plants and the ground less energy, making it harder for life to thrive.
Light behaves like tiny particles called photons.
When photons arrive at a low angle in winter, more are reflected (like skipping rocks) instead of being absorbed, so less heat stays.
In summer, photons hit the ground straight on, are absorbed, and increase ground temperature.

Key Terms & Definitions

Axis tilt — The slant of Earth's rotational axis, responsible for seasonal changes.
Photon — A tiny particle of light.
Reflection — Light bouncing off a surface instead of being absorbed.
Equator — The midpoint latitude of Earth, dividing Northern and Southern Hemispheres.

Action Items / Next Steps

Review how sunlight angle and daylight duration affect temperature.
Be able to explain why angle is more important than daylight length for seasonal temperature changes.