How big is Distance from Earth to the Sun?

Earth is about 150 million kilometers (93 million miles) from the Sun on average. The distance changes a little through the year, because Earth's orbit is not a perfect circle. The average is so useful that astronomers made it a unit of length, the astronomical unit, now defined as exactly 149,597,870,700 meters.

Distance

Earth travels around the Sun on an ellipse, a slightly stretched circle. It is closest to the Sun, about 147.1 million kilometers (91.4 million miles) away, in early January. It is farthest, about 152.1 million kilometers (94.5 million miles) away, in early July. In 2026 those dates are January 3 and July 6.

The difference is about 5 million kilometers, or about 3%. That is too small to cause the seasons. They come from the 23.4-degree tilt of Earth's axis, which is why the Northern Hemisphere has winter when Earth is closest to the Sun.

At the average distance, sunlight takes about 8 minutes and 19 seconds to reach Earth. The Sun seen in the sky is the Sun as it was about 8 minutes earlier.

Size comparisons

About 11,700 Earths lined up side by side would span the distance.
It is about 389 times the average distance from Earth to the Moon, far enough to travel to the Moon and back about 195 times.
Rigel, a blue supergiant star and the next smaller object in the explorer, is about 110 million kilometers across, about three-quarters of this distance.
If the Sun were shrunk to the size of a basketball, Earth would be a bead about 2 millimeters wide, orbiting about 26 meters (85 feet) away.
A car driving nonstop at 100 kilometers per hour (62 miles per hour) would take about 170 years to cover it.

How the distance was measured

Astronomers once knew the relative distances of the planets far better than their actual distances. In 1716 Edmond Halley described how to measure the Sun's distance using a transit of Venus, when Venus passes across the face of the Sun as seen from Earth. Observers at widely separated places would time the transit precisely, and combining their timings would reveal the distance.

Expeditions observed the transits of 1761 and 1769 from places including South Africa, Siberia, Norway and Tahiti. They gave astronomers their first good value for the distance to the Sun. In 1771 the French astronomer Lalande combined the results into a distance of about 153 million kilometers, about 2% more than the modern value.

A unit of length

Astronomers measure distances within the Solar System in astronomical units. Until 2012, the unit was defined through the Sun's gravity, so that the planets' distances could be given accurately as ratios even when their true distances were uncertain.

Modern measurements are precise enough that this is no longer needed. In 2012 the International Astronomical Union, the international organization of professional astronomers, fixed the astronomical unit at exactly 149,597,870,700 meters. It chose that value to be close to the distance from Earth to the Sun. The unit's symbol is au.