By John Lindell
Updated Mar 24, 2022
The time it takes for Earth to complete a rotation on its axis is called a day, while the period for a full orbit around the Sun is a year. This article breaks down both timescales and explains why they matter.
Earth rotates about an imaginary line that runs from the North Pole to the South Pole. Unlike a perfectly vertical spin, this axis is tilted 23.5°, giving our planet the appearance of a spinning top. The tilt, not the distance to the Sun, drives the seasonal cycle.
Relative to the Sun, Earth needs exactly 24 hours to complete one full turn—this is the solar day. However, when measured against the background stars, the planet turns in 23 hours, 56 minutes, and 4 seconds, known as the sidereal day. The difference arises because Earth is also moving along its orbit while spinning.
It takes 365 days and 5 hours for Earth to travel once around the Sun. The orbital path, called the ecliptic, is slightly elliptical: Earth’s closest approach (perihelion) is 91 million miles, and its farthest point (aphelion) is 95 million miles from the Sun.
Other planets spin and orbit at different rates. Mercury, for instance, completes a full orbit in 88 Earth days (about one quarter of Earth’s year) and rotates on its axis in roughly 59 Earth days. Jupiter, by contrast, orbits the Sun in 12 Earth years but whirls around its axis in less than 10 Earth hours.
The 23.5° tilt of Earth’s axis means that as the planet orbits the Sun, one hemisphere is alternately angled toward or away from the Sun. The hemisphere facing the Sun experiences spring and summer, while the opposite side experiences autumn and winter.
