Astronomical Unit

Domain	Definition
Aerospace	1. A unit of length, usually defined as the distance from the earth to the sun, 149,599,000 kilometers. This value for the AU was derived from radar observations of the distance of Venus. The value given in astronomical ephemerides, 149,500,000 kilometers, was derived from observations of the minor planet Eros. 2. The unit of distance in terms of which, in the Kepler Third Law,n2a3 = k2(1+m), the semimajor axis a of an elliptical orbit must be expressed in order that the numerical value of the Gaussian constant k may be exactly 0.01720209895 when the unit of time is the ephemeris day.In astronomical units, the mean distance of the earth from the sun, calculated by the Kepler law from the observed mean motion n and adopted mass m, is 1.00000003.Abbreviation AU. (references)
Computing	A transfer mode in which the information is organized into cells, it is asynchronous in the sense that the recurrence of cells depends on the required or instantaneous bit rate. Source: European Union. (references)
Geography	The distance from the Earth to the sun. Source: European Union. (references)
Physics	149,597,870 km; the average distance from the Earth to the Sun. (AU). (references)
Solar	The mean earth-sun distance, equal to 1.496E+13cm or 214.94 solar radii. (AU). (references)
Space	(AU). Mean Sun-Earth distance, used as scaling distance in the solar system. Using Kepler's laws, it is easy to derive distances in this system as measured in astronomical units. Independent measurement of one distance in that system then fixes the magnitude of all the rest. (references)
	The mean Sun-Earth distance, a unit of distance widely used in expressing distances in the solar system. 1 AU = 149,600,000 km = 92,957,000 miles. (AU). (references)
Source: compiled by the editor from various references; see credits.

Specialty Definition: Astronomical unit

An astronomical unit (AU) is a unit of distance, approximately equal to the mean distance between the Earth and Sun. Earth's orbit is not a circle but an ellipse; originally, the AU was defined as the length of the semimajor axis of said orbit. For greater precision, the IAU in 1976 defined the AU as the distance from the Sun at which a particle of negligible mass, in an unperturbed orbit, would have an orbital period of 365.2568983 days (a Gaussian year). The AU is thus defined as 1.4959787066E+11mm (about 150 million kilometres).

At the time the AU was introduced, its actual value was very poorly known, but planetary distances in terms of AU could be determined from heliocentric geometry and the laws of planetary motion. Eventually the actual value of the AU was determined (approximately) from parallax observations, and more recently (and precisely) by radar. While the value of the astronomical unit is now known to great precision, the value of the mass of the Sun is not because of uncertainty in the value of the gravitational constant. Because the gravitational constant is known to only five or six significant digits while the positions of the planets are known to 11 or 12 digits, it is impossible to do calculations about the position of the planets in SI units without losing precision in the unit conversion. Therefore calculations in celestial mechanics are performed in solar masses and astronomical units rather than in kilograms and kilometers.

Examples

Pluto is 39.5 AU from the Sun.
Jupiter is 5.2 AU from the Sun.
Mean diameter of Betelgeuse is 2.57 AU.
The Moon is 0.0026 AU from the Earth.

Some approximate conversion factors:

1 AU = 149,600,000 km = 92,960,000 miles = 490,800,000,000 feet
1 ly (light-year) = 63,240 AU

External link

Conversion Calculator for Units of LENGTH: http://www.ex.ac.uk/cimt/dictunit/ccleng.htm

Synonyms within Context: Astronomical Unit

Frequency of Internet Keywords: Astronomical Unit

Modern Translation: Astronomical Unit

Language		Translations for "Astronomical Unit"; alternative meanings/domain in parentheses.
Danish		astronomisk enhed, AE (United Arab Emirates). (various references)

Dutch		astronomische eenheid, AE (Avian encephalomyelitis Epidemic tremor, United Arab Emirates). (various references)

Finnish		tähtitieteellinen yksikkö. (various references)

French		unité astronomique, UA, U.a.. (various references)

German		astronomische Einheit, A.E.. (various references)

Greek		αστρονομική μονάδα. (various references)

Italian		unita'astronomica, unit� astronomica, ua (actual zone of indecision, Ukraine). (various references)

Pig Latin		astronomicalay itunay

Portuguese		unidade astronómica. (various references)

Spanish		unidad astronómica (astronomic unit). (various references)
Source: compiled by the editor from various translation references.

Anagrams: Astronomical Unit

Scrabble® Enable2K-Verified Anagrams
	Words within the letters "a-a-c-i-i-l-m-n-n-o-o-r-s-t-t-u"
	-2 letters: matriculations.
	-3 letters: antiromantics, articulations, calumniations, columniations, contaminators, instructional, malnutritions, matriculation, translocation.
	-4 letters: antiromantic, articulation, astronomical, calumniation, calumniators, columniation, consultation, contaminator, continuators, culminations, incrustation, inoculations, inosculation, instauration, lacrimations, malnutrition, matriculants, naturalistic, nonautomatic, onomastician, transitional.
	-5 letters: acrimonious, anastomotic, antimonials, antimusical, antitumoral, astronautic, automations, calumniator, continuator, contritions, culinarians, culmination, inoculation, inoculators, instinctual, instruction, lacrimation, laminations, maculations, marinations.
Source: compiled by the editor from various references; see credits. SCRABBLE® is a registered trademark. All intellectual property rights in and to the game are owned in the U.S.A and Canada by Hasbro Inc., and throughout the rest of the world by J.W. Spear & Sons Limited of Maidenhead, Berkshire, England, a subsidiary of Mattel Inc. Mattel and Spear are not affiliated with Hasbro.

Context	Synonyms within Context (source: adapted from Roget's Thesaurus).
Length	Astronomical unit, AU, light-year, parsec.
Source: adapted from Roget's Thesaurus.

Expression	Frequency per Day
astronomical unit	29
Source: compiled by the editor from various references; see credits.

Astronomical Unit

Definition: Astronomical Unit