Earth and Space Science / Unit 9: The Solar System
9.5 Seasons
Notes
Seasons are caused by Earth's axial tilt of 23.5°, not by distance from the Sun.
- When the Northern Hemisphere tilts toward the Sun it gets more direct sunlight and longer days: summer.
- Solstices (about June 21 and December 21) are the longest and shortest days. Equinoxes (about March 20 and September 22) have nearly equal day and night.
- Earth is actually closest to the Sun in early January (perihelion).
- Near the equator, seasons are weak.
- When it is summer in the north, it is winter in the south.
Practice
What causes the seasons?
Tilt changes the angle and duration of sunlight.
When the Northern Hemisphere has summer, the Southern Hemisphere has:
Hemispheres are tilted oppositely.
Around December 21 in the Northern Hemisphere there is:
Shortest day of the year.
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