Why seasons happen — Science, 7–10 years
Seasons happen because Earth is tilted as it travels around the Sun, changing how sunlight reaches each place.
The idea
Earth is tilted rather than standing straight up as it travels around the Sun. For part of the journey, your half of Earth leans towards the Sun: sunlight is more direct and days are longer, so it is warmer. Later, it leans away: light is less direct and days are shorter.
Why it matters
People needed to predict when plants would grow, when ice might melt and how long daylight would last. The puzzle was that the Sun seems to move across the sky in the same daily way, yet the year changes. Earth’s tilt and orbit explain that repeating pattern.
A worked example
Imagine Earth’s Northern Hemisphere tilted towards the Sun in June. Step one: sunlight hits it more directly, spreading over a smaller area. Step two: daylight lasts longer. Step three: the ground receives more energy each day, so temperatures often rise. At the same time, the Southern Hemisphere has winter.
A common trap
Many people think summer happens because Earth is much closer to the Sun. That seems sensible: closer things often feel warmer. But Earth’s small change in distance is not the main cause. The tilt changes the angle and length of sunlight, and the two hemispheres have opposite seasons.
Where it is used
Seasonal changes help people decide when to plant crops, prepare buildings and plan journeys. Animals and plants also respond to changing daylight and temperature, for example by growing, flowering or migrating. The pattern differs by place: near the Equator, seasonal temperature changes may be smaller.
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