astronomical unit

noun

: a unit of length used in astronomy equal to the mean distance of the earth from the sun or about 93 million miles (150 million kilometers)

Examples of astronomical unit in a Sentence

Recent Examples on the Web

These are all typical features of a comet that is still 3.8 astronomical units (Earth-sun distances; one AU is about 93 million miles, or 149.6 million km) from the sun. —Keith Cooper, Space.com, 8 Aug. 2025

Astronomers use the distance between the Earth and the sun — one astronomical unit or au — to measure distance in the solar system. —Jamie Carter, Forbes.com, 15 July 2025

The distance between the exoplanet and its star, GJ 504, is 44 astronomical units (au), around the same distance between the sun and Pluto in our solar system. —Kenna Hughes-Castleberry, Space.com, 23 June 2025

The Kuiper Belt begins about 30 astronomical units (AU) from the sun (one AU is the distance of Earth from the sun), its inner edge guarded by Neptune, and extends out to 50 AU. —Keith Cooper, Space.com, 30 May 2025

Word History

First Known Use

1848, in the meaning defined above

Rhymes for astronomical unit

• lunate
• multiunit
• subunit

Kids Definition

astronomical unit

noun

: a unit of length used in astronomy equal to the average distance of the earth from the sun or about 93 million miles (150 million kilometers)