astronomical unit

American  

noun

Astronomy.

1. a unit of length, equal to the mean distance of the earth from the sun: approximately 93 million miles (150 million km). AU

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astronomical unit British  

noun

1. a unit of distance used in astronomy equal to the mean distance between the earth and the sun. 1 astronomical unit is equivalent to 1.495 × 10 ¹¹ metres or about 9.3 × 10 ⁷ miles

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astronomical unit Scientific  

/ ăs′trə-nŏm′ĭ-kəl /

1. A unit of length equal to the average distance from Earth to the Sun, approximately 149.6 million km (92.8 million mi). It is used especially to measure distances within the solar system.

2. Compare light-year parsec

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astronomical unit Cultural  

1. The mean distance between the Earth and the sun, about 93 million miles or 150 million kilometers. It is often abbreviated as AU.

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Etymology

Origin of astronomical unit

First recorded in 1900–05

Compare meaning

How does astronomical-unit compare to similar and commonly confused words? Explore the most common comparisons:

• astronomical unit vs. light-year

Example Sentences

The debris cloud around Gaia20ehk appears to orbit the star at about one astronomical unit, which is roughly the same distance between Earth and the sun.

From Science Daily • Mar. 11, 2026

The average distance between Earth and the sun, what astronomers call an astronomical unit, is defined as 149,597,870.7 km.

From Scientific American • Jun. 30, 2023

“So. We’re near Dralee, right? That means the gate is about a half an astronomical unit from this location if we—” “The gate does not exist.”

From The Verge • Jun. 11, 2019

In particular, 1 astronomical unit is defined to be the average distance from Earth to the Sun, and is now recognized to be 149,597,870,700 m or, approximately 93,000,000 mi.

From Textbooks • Mar. 30, 2016

An astronomical unit is the distance of the Earth from the Sun.

From "Cosmos" by Carl Sagan