What is the average distance from Earth to the Sun in millions of kilometers?

The average distance from Earth to the Sun is about 150 million kilometers. Astronomers define this distance more precisely as one astronomical unit, or 149,597,870.7 kilometers exactly.

Earth does not travel around the Sun in a perfect circle. Its orbit is an ellipse, so the distance changes during the year: Earth is closest at perihelion and farthest at aphelion. The average value is used because it provides a convenient standard for describing distances throughout the Solar System.

The astronomical unit became an important measuring tool in astronomy because kilometers quickly become unwieldy for planetary distances. One AU is also about 499 light-seconds, meaning sunlight takes roughly 8 minutes 19 seconds to reach Earth.

A common mix-up is treating 150 million kilometers as a fixed distance. It is a rounded average, not the exact separation on every day of the year. The International Astronomical Union adopted the exact modern definition in 2012.