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
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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 Read More: Our Solar System May Have a New Dwarf Planet Orbiting Even Farther Than Pluto Crowded Clusters and Far-Flung Planets Though some planets orbit their stars closely, there are some planets that circle their stars from afar, from hundreds or thousands of astronomical units (AU) away. Sam Walters, Discover Magazine, 28 May 2025 The companion's orbit relative to the central star is a bit lopsided, ranging from about two astronomical units (AU, the typical Earth-Sun distance) at its closest approach to roughly three AU at its farthest. John Timmer, ArsTechnica, 22 May 2025 The amount of movement on the sky would be tiny — about three arcminutes per year at a distance of approximately 700 astronomical units (AU). Keith Cooper, Space.com, 1 May 2025 See All Example Sentences for astronomical unit

Word History

First Known Use

1848, in the meaning defined above

Time Traveler
The first known use of astronomical unit was in 1848

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Cite this Entry

“Astronomical unit.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/astronomical%20unit. Accessed 13 Jun. 2025.

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)

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