We have seasons because Earth's axis is tilted about 23.4 degrees relative to its orbit around the Sun. This tilt causes different parts of Earth to receive varying amounts of direct sunlight throughout the year as Earth orbits the Sun. When the Northern Hemisphere is tilted toward the Sun, it experiences summer with more direct sunlight and longer days, while the Southern Hemisphere, tilted away from the Sun, experiences winter with less direct sunlight and shorter days. The reverse happens six months later, creating opposite seasons in the two hemispheres. The axial tilt and Earth’s consistent orientation relative to the Sun are the main reasons for seasonal changes, not the distance from the Sun.
Key Points about Seasons
- Earth's axis is tilted at about 23.4 degrees.
- The tilt causes varying angles and durations of sunlight on different parts of Earth during its orbit.
- This results in temperature changes and weather patterns that define the seasons.
- Opposite hemispheres have opposite seasons at any given time due to the tilt.
- Distance to the Sun changes little and does not cause the seasons.
Additional Detail on Earth’s Tilt
The tilt likely resulted from a massive collision early in Earth’s history, which also contributed to the formation of the Moon. As Earth orbits the Sun, its tilted axis stays pointed in the same direction, so the angle of sunlight changes with the seasons. This explains why in June the Northern Hemisphere receives more direct sunlight and in December the Southern Hemisphere does.
This axial tilt and orbit configuration cause the sequence of spring, summer, autumn, and winter experienced in temperate regions.
