astronomical unit


Definition of astronomical unit

: 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

The previous record holder orbited the sun at about 120 AU (one AU, or astronomical unit, is the distance from the Earth to the sun). David Grossman, Popular Mechanics, "Move Over, Farout: FarFarOut Has Been Discovered," 25 Feb. 2019 At an orbital distance of 600 astronomical units (1 AU is the distance between Earth and the sun), Planet Nine would be 160,000 times dimmer than Neptune is at 30 AU. Quanta Magazine, "Why Can’t We Find Planet Nine?," 3 July 2018 Farout orbits the sun at about 120 astronomical units (AU)—in other words, 120 times as far from the sun as Earth is. Avery Thompson, Popular Mechanics, "Scientists Find the Most Distant Solar System Object Yet," 17 Dec. 2018 Some simple numbers to spell it out: Distance in the solar system is measured in astronomical units (AU), which is the distance between Earth and the sun. John Wenz, Popular Mechanics, "Why Voyager 2 Is In Interstellar Space But Not Out of the Solar System," 13 Dec. 2018 Sedna's elliptical orbit takes it as close to the sun as 76 astronomical units (AU; the Earth-sun distance, about 93 million miles, or 150 million kilometers) and as far away as 936 AU. Nola Taylor Redd,, "No Need for Planet Nine? Small Objects' Gravity Could Explain Weird Orbits," 5 June 2018 At this week’s pass, the asteroid will be about .07 astronomical units or about 6.5 million miles away — the equivalent of about 30 trips between our pale blue planet and the moon. Blaine Friedlander, Washington Post, "The biggest meteor shower of the year peaks tonight. Here’s how to watch.," 13 Dec. 2017 Gliese 710 will be about 16,000 astronomical units away from the sun. Jason Daley, Smithsonian, "2.8 Million Stars Sparkle in This Incredible Image of the Milky Way," 6 Sep. 2017 For instance, the object takes 1,100 earth years to orbit the sun in an elliptical orbit that brings it as close as 38 astronomical units (the distance of the earth to the sun) and as far as 180 AUs. Jason Daley, Smithsonian, "Meet DeeDee, the Solar System’s Newest Dwarf Planet (Maybe)," 14 Apr. 2017

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'astronomical unit.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

See More

First Known Use of astronomical unit

1848, in the meaning defined above

Keep scrolling for more

Learn More about astronomical unit

Statistics for astronomical unit

Last Updated

22 Jul 2019

Look-up Popularity

Time Traveler for astronomical unit

The first known use of astronomical unit was in 1848

See more words from the same year

More from Merriam-Webster on astronomical unit Encyclopedia article about astronomical unit

Comments on astronomical unit

What made you want to look up astronomical unit? Please tell us where you read or heard it (including the quote, if possible).


formidable, illustrious, or eminent

Get Word of the Day daily email!

Test Your Vocabulary

The Exceptions Quiz III

  • one green toy robot amidst many red toy robots
  • Which of these words does not mean "nonsense"?
How Strong Is Your Vocabulary?

Test your vocabulary with our 10-question quiz!

Word Winder's CrossWinder

Test Your Knowledge - and learn some interesting things along the way.

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!