astronomical unit


astronomical unit
(ua or au or AU)
   a unit of distance used by astronomers to measure distances in the Solar System. One astronomical unit equals the "average" distance from the center of the Earth to the center of the Sun (mathematically, it is the length of the semimajor axis of the Earth's elliptical orbit, which is the ordinary average of the Earth's minimum and maximum distances from the Sun). The currently accepted value, adopted in 1996, is 149 597 870 691 meters (1.495 978 706 91 x 108 kilometers or about 92 955 807 miles), with an uncertainty of about 30 meters. The astronomical unit is a convenient yardstick for measuring the distances between objects in the Solar System. Astronomers find it particularly convenient to use astronomical units in solving the equations of planetary motion. Because these equations are the same regardless of the unit used for distance, the predictions they generate will remain correct even if future astronomers determine a slightly different length for the distance between the Earth and Sun. This unit is accepted for use with SI units. The official symbol for the unit is ua, but the symbol au is common in English-speaking countries. Note that AU is also used as the symbol for the absorbance unit (see above).

Dictionary of units of measurement. 2015.

Look at other dictionaries:

  • astronomical unit — n. Astron. a unit of length based on the mean distance of the earth from the sun, c. 149.6 million km ( c. 93 million mi): light travels this distance in c. 8.3 minutes: abbrev. AU …   English World dictionary

  • Astronomical unit — This article is about unit of length. For the full system of units, see Astronomical system of units. 1 astronomical unit = SI units 149.60×10^6 km 149.60×10^9 m Astronomical units 4.8481 …   Wikipedia

  • astronomical unit — Astron. a unit of length, equal to the mean distance of the earth from the sun: approximately 93 million miles (150 million km). Abbr.: AU [1900 05] * * * ▪ unit of measurement        Comparative data for the Sun, planets, and other solar system… …   Universalium

  • astronomical unit — UK / US noun [countable] Word forms astronomical unit : singular astronomical unit plural astronomical units astronomy a unit for measuring distance in space …   English dictionary

  • Astronomical Unit — noun a unit of length used for distances within the solar system; equal to the mean distance between the Earth and the Sun (approximately 93 million miles or 150 million kilometers) (Freq. 1) • Syn: ↑AU • Hypernyms: ↑astronomy unit * * *… …   Useful english dictionary

  • Astronomical Unit —    A unit of distance used to measure orbits and trajectories within the solar system. An Astronomical Unit is the average distance between the Sun and Earth. One AU is roughly equal to 149,600,000 km (92,956,000 mi.). To give you an idea of the… …   The writer's dictionary of science fiction, fantasy, horror and mythology

  • astronomical unit — astronominis vienetas statusas T sritis Standartizacija ir metrologija apibrėžtis Apibrėžtį žr. priede. priedas( ai) Grafinis formatas atitikmenys: angl. astronomical unit vok. astronomische Einheit, f rus. астрономическая единица, f pranc. unité …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

  • astronomical unit — astronominis vienetas statusas T sritis fizika atitikmenys: angl. astronomical unit vok. Astronomische Einheit, f rus. астрономическая единица, f pranc. unité astronomique, f …   Fizikos terminų žodynas

  • astronomical unit — unit of distance equal to the distance from the earth to the sun Units of Measurement …   Phrontistery dictionary

  • astronomical unit — /ˌæstrənɒmɪkəl ˈjunət/ (say .astruhnomikuhl yoohnuht) noun a unit, defined as 149 597 870 km, approximately equal to the mean distance between the centre of the earth and the centre of the sun, used as a unit of distance in astronomy. Symbol: AU… …   Australian English dictionary

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