Science · Solar system
Earth's tilt & seasons
Why seasons happen as Earth orbits the Sun.
Why Do We Have Seasons?
Earth travels around the Sun once every year. That journey is called an orbit. But Earth does not stand up straight as it orbits. Earth is tilted to one side, like a spinning top leaning over. This tilt is the reason we have seasons. When your part of Earth leans toward the Sun, you get summer. When it leans away from the Sun, you get winter. The tilt stays the same direction all year round.
Earth's Tilt
Imagine Earth with a stick through the middle from top to bottom. That stick is called Earth's axis. The axis is tilted at an angle. It never changes direction as Earth moves around the Sun. Because of this tilt, different parts of Earth face the Sun more directly at different times of year. When the North Pole tilts toward the Sun, countries in the north have summer. At the same time, the South Pole tilts away, so countries in the south have winter.
Sunlight and Warmth
When sunlight hits Earth straight on, it warms the ground more. When sunlight hits at a slant, it spreads out over a bigger area. That means less warmth in each spot. In summer, your part of Earth tilts toward the Sun. Sunlight hits more directly, so days are warmer and longer. In winter, your part tilts away. Sunlight comes in at a slant, so days are cooler and shorter.
The Orbit Stays the Same
Earth does not move closer to or farther from the Sun to make seasons. The distance stays nearly the same all year. Only the tilt matters. Spring and autumn happen when neither pole tilts much toward the Sun. During these seasons, day and night are nearly equal in length. The tilt causes all four seasons as Earth completes its yearly orbit.
Worked examples
1. It is summer in Australia. What season is it in England at the same time?
- Australia is in the Southern Hemisphere, below the equator.
- England is in the Northern Hemisphere, above the equator.
- When the Southern Hemisphere tilts toward the Sun, the Northern Hemisphere tilts away.
- So if Australia has summer, England has winter.
2. Why is it warmer in summer even though Earth stays the same distance from the Sun?
- In summer, your part of Earth tilts toward the Sun.
- Sunlight hits the ground more directly, not at a slant.
- Direct sunlight warms each spot more than slanted sunlight.
- The tilt causes the warmth, not the distance from the Sun.
3. During which seasons are day and night nearly equal in length?
- In spring and autumn, neither pole tilts much toward the Sun.
- Both hemispheres get similar amounts of sunlight.
- Day and night are nearly equal during these seasons.
- Summer and winter have unequal day and night lengths.
Try it yourself
The North Pole tilts toward the Sun. What season is it in Canada?
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