Seasons come from the tilt of Earth's axis. Earth is tilted by about 23 and a half degrees, and as it goes around the Sun, the tilt always points the same way in space. Earth's changing distance from the Sun is too small to cause the seasons.
In summer, the Sun is higher in the sky, and its rays hit the ground more directly. That makes summer warmer. When rays hit the ground at a slant, they spread out over more ground and warm it less. That is part of why winter is cold. Summer days also have more hours of sunlight.
The Sun is directly overhead at noon only between the Tropic of Cancer and the Tropic of Capricorn. Outside those two lines the Sun is never straight overhead. On about June 21 it is over the Tropic of Cancer, and around December 21 it is over the Tropic of Capricorn.
Near the equator it stays warm all year, and the seasons are wet and dry instead of warm and cold. Near the poles the amount of daylight changes dramatically. At the South Pole the Sun stays up all summer and stays down all winter, so days and nights last half a year.
Water warms and cools much more slowly than land. A place near a big ocean has smaller seasonal changes than a place in the middle of a continent.
Earth's orbit is slightly squashed, so Earth is a little closer to the Sun at some times of year and a little farther at others. As of November 2026, Earth is closest to the Sun in early January, in the middle of northern winter. It is farthest in July.
The calendar days still matter. The spring equinox is usually on March 20, and the fall equinox is usually on September 22. At both, Earth's axis points neither toward nor away from the Sun, and day and night are about equal in length.
Living things follow the Sun too. In late summer the days get shorter, and that tells trees to make less green chlorophyll. Less chlorophyll lets other colors show. Some animals migrate when the seasons change, traveling a long way to a winter home.
Words to know
- tropic: overhead line
- equator: middle line
- continent: huge land
- chlorophyll: leaf's green
