Earth in Orbit

Earth follows a slightly elliptical orbit around the Sun at an average distance of about 93 million miles (150 million kilometers). This distance is called one astronomical unit, or AU.

Earth completes one orbit in approximately 365.25 days, which determines the length of our year. To account for the extra quarter day, most calendars add a leap day every four years, except for century years that are not evenly divisible by 400.

Earth travels around the Sun at an average speed of about 67,000 miles per hour (107,000 kilometers per hour). Because its orbit is slightly elliptical, Earth moves a little faster near perihelion, its closest point to the Sun in early January, and a little slower near aphelion, its farthest point in early July.

This change in distance is relatively small. Earth's seasons are caused primarily by the planet's axial tilt of about 23.5 degrees, not by its varying distance from the Sun.

Key Features of Earth’s Orbit

Earth's orbital plane is called the ecliptic. The other planets orbit close to this same general plane, which is why the Sun and planets appear to follow similar paths across our sky.

Earth's orbit has low eccentricity, meaning it is close to circular. Over immense periods, gravitational interactions with other planets gradually change the shape and orientation of that orbit.

Earth and the Moon travel together around the Sun, while the Moon completes an orbit around Earth in about 27.3 days. Changes in the alignment of Earth, the Moon, and the Sun create lunar phases and, when the geometry is precise, solar or lunar eclipses.

Seasons and Orbital Motion

As Earth travels around the Sun, its axis remains pointed in nearly the same direction in space. When the Northern Hemisphere tilts toward the Sun, it receives more direct sunlight and experiences longer days, producing summer there.

Six months later, the Northern Hemisphere tilts away from the Sun while the Southern Hemisphere tilts toward it. This geometry creates opposite seasons in the two hemispheres and influences climate, ecosystems, agriculture, and the constellations visible at night.

Human Activity in Earth Orbit

Earth orbit is an important region for human activity. Satellites support communications, navigation, weather forecasting, scientific research, and Earth observation. Low Earth orbit is also home to the International Space Station.

Understanding Earth's motion is essential for satellite operations, launch planning, and timing missions to destinations throughout the Solar System.

Long-Term Orbital Changes

Over tens to hundreds of thousands of years, gravitational interactions with other planets slowly alter Earth's orbital shape, axial tilt, and orientation. Together, these variations are known as Milankovitch cycles and contribute to long-term climate patterns, including the timing of ice ages.

Earth's nearly circular orbit, together with its atmosphere, oceans, and favorable distance from the Sun, has helped maintain conditions where liquid water and complex life can exist.