Rotation and revolution

Section 1Two motions, happening together

Earth moves in two ways at the same time. Rotation is spinning on its own axis — one full spin every 24 hours. Revolution is travelling around the Sun — one full orbit every 365.25 days. The two motions cause different things.

Section 2Rotation — what it causes

Earth rotates on its axis from west to east (this is why the Sun appears to rise in the east and set in the west). One full rotation takes about 24 hours. Rotation causes day and night, time zones, and the apparent daily motion of the Sun and stars.

Section 3Revolution — what it causes

Earth orbits the Sun in a nearly circular path, taking about 365.25 days. The extra quarter-day is why we add a leap day (Feb 29) every 4 years. Earth's axis is tilted at 23.5° and stays pointed in the same direction throughout the orbit, which means different parts of Earth lean toward the Sun at different times — and that gives us seasons.

Section 4Why we have seasons

When the Northern Hemisphere tilts toward the Sun, the North has summer and the South has winter. Six months later, the opposite is true. The tilt — not the distance from the Sun — is what drives seasons. Equinoxes (around March and September) are when neither hemisphere is tilted toward the Sun.