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1 astronomical unit =
SI units
149. 60×106 km 149. The kilometre ( American spelling: kilometer) symbol km is a unit of Length in the Metric system, equal to one thousand 60×109 m
Astronomical units
4. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International 8481×10-6 pc 15. History The first direct measurements of an object at interstellar distances were undertaken by German Astronomer Friedrich Wilhelm Bessel in 1838 813×10−6 ly}}
US customary / Imperial units
92. A light-year or light year (symbol ly) is a unit of Length, equal to just under ten trillion Kilometres As defined by US customary units, also known in the United States as English units or Imperial units (in reference to the British Empire) (but see English Imperial units or the Imperial system is a collection of units first defined in the British Weights and Measures Act of 1824 956×106 mi 490. A mile is a unit of Length, usually used to measure Distance, in a number of different systems including Imperial units United States 81×109 ft

The astronomical unit (AU or au or a. A foot (plural feet or foot; symbol or abbreviation ft or sometimes &prime – the prime symbol) is a non-SI unit u. or sometimes ua) is a unit of length of approximately 150 million kilometres, and is based on the distance from the Earth to the Sun. Length is the long Dimension of any object The length of a thing is the distance between its ends its linear extent as measured from end to end The kilometre ( American spelling: kilometer) symbol km is a unit of Length in the Metric system, equal to one thousand EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 The Sun (Sol is the Star at the center of the Solar System. The precise value of the AU is currently accepted as 149,597,870,691 ± 30 metres (nearly 150 million kilometres or 93 million miles). ± The

The symbol ua is recommended by the Bureau International des Poids et Mesures[1] but in anglophone countries the reverse - au - is more common. The International Bureau of Weights and Measures ( Bureau international des poids et mesures, in French) is an international Standards organization, one An Anglophone (or anglophone) is someone who speaks the English language. The International Astronomical Union recommends au[2] and international standard ISO 31-1 uses AU. International standards are Standards developed by international Standards organisations International standards are available for consideration and use worldwide ISO 31-1 is the part of International standard ISO 31 that defines names and symbols for quantities and units related to Space In general, capital letters are only used for the symbols of units which are named after individual scientists, while au or a. u. can also mean atomic unit or even arbitrary unit; however, the use of AU to refer to the astronomical unit is widespread. Atomic units ( au) form a System of units convenient for Atomic physics, Electromagnetism, and Quantum electrodynamics, especially

Originally, the AU was defined as the length of the semi-major axis of the Earth's elliptical orbit around the Sun. Length is the long Dimension of any object The length of a thing is the distance between its ends its linear extent as measured from end to end In Geometry, the semi-major axis (also semimajor axis) is used to describe the dimensions of ellipses and hyperbolae The Sun (Sol is the Star at the center of the Solar System. In 1976, the International Astronomical Union revised the definition of the AU for greater precision, defining it as the distance from the centre of the Sun at which a particle of negligible mass, in an unperturbed circular orbit, would have an orbital period of 365. In physical theories, a test particle is an idealized model of an object whose physical properties (usually Mass, Charge, or size) are assumed Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object The orbital period is the time taken for a given object to make one complete Orbit about another object 2568983 days (one Gaussian year). A Gaussian year is defined as 3652568983 Days It was adopted by Carl Friedrich Gauss as the length of the Sidereal year in his studies of the dynamics This definition gives a value that is slightly less than the mean Earth-Sun distance. An alternative way of stating the definition is that an AU is the distance at which the heliocentric gravitational constant (the product GM☉) is equal to (0. The gravitational constant, denoted G, is a Physical constant involved in the calculation of the gravitational attraction between objects with mass 017 202 098 95)² AU³/d².

Contents

History

Aristarchus of Samos estimated the distance to the Sun to be about 20 times the distance to the moon, whereas the true ratio is about 390. Aristarchus (Ἀρίσταρχος 310 BC - ca 230 BC) was a Greek Astronomer and Mathematician, born on the island of His estimate was based on the angle between the half moon and the sun, which he estimated as 87°.

According to Eusebius of Caesarea in the Praeparatio Evangelica, Eratosthenes found the distance to the sun to be "σταδιων μυριαδας τετρακοσιας και οκτωκισμυριας" (literally "of stadia myriads 400 and 80000"). Προπαρασκευη Ευαγγελικη ('Preparation for the Gospel', commonly known by its Latin title Praeparatio evangelica, was a work by Eratosthenes of Cyrene ( Greek; 276 BC - 194 BC was a Greek Mathematician, Poet, athlete, Geographer and Myriad is a classical Greek name for the Number 104 = 10000. In modern English the word refers to an unspecified large quantity This has been translated either as 4,080,000 stadia (1903 translation by Edwin Hamilton Gifford), or as 804,000,000 stadia (edition of Édouard des Places, dated 1974-1991). Stadiametric rangefinding, or the stadia method is a technique of measuring distances with a telescopic instrument. Using the Greek stadium of 185 to 190 metres, the former translation comes to a far-too-low 755,000 km, whereas the second translation comes to 148. 7 to 152. 8 million km (accurate within 2%).

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 Kepler's laws of planetary motion. In Astronomy, Kepler's Laws of Planetary Motion are three mathematical laws that describe the motion of Planets in the Solar System. The value of the AU was first estimated by Jean Richer and Giovanni Domenico Cassini in 1672. Jean Richer (1630 - 1696 was a French Astronomer and assistant ( élève astronome) of Giovanni Domenico Cassini. Giovanni Domenico Cassini ( June 8, 1625 &ndash September 14, 1712) was an Italian Mathematician, Astronomer By measuring the parallax of Mars from two locations on the Earth, they arrived at a figure of about 140 million kilometres. Parallax is an apparent displacement or difference of orientation of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between

A somewhat more accurate estimate can be obtained by observing the transit of Venus. A transit of Venus across the Sun takes place when the Planet Venus passes directly between the Sun and Earth, obscuring a small portion of the This method was devised by James Gregory and published in his Optica Promata. James Gregory (November 1638 &ndash October 1675 was a Scottish Mathematician and Astronomer. It was strongly advocated by Edmond Halley and was applied to the transits of Venus observed in 1761 and 1769, and then again in 1874 and 1882. Edmond Halley FRS (ˈɛdmənd ˈhɔːlɪ ( November 8, 1656 &ndash January 14, 1742) was an English Astronomer

Another method involved determining the constant of aberration, and Simon Newcomb gave great weight to this method when deriving his widely accepted value of 8. The aberration of light (also referred to as astronomical aberration or stellar aberration) is an astronomical phenomenon which produces an Apparent motion Simon Newcomb ( March 12 1835 &ndash July 11 1909) was a Canadian American Astronomer and Mathematician 80″ for the solar parallax (close to the modern value of 8. Parallax is an apparent displacement or difference of orientation of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between 794148″).

The discovery of the near-Earth asteroid 433 Eros and its passage near the Earth in 1900–1901 allowed a considerable improvement in parallax measurement. Near-Earth asteroids (NEAs are Asteroids whose Orbits are close to Earth 's orbit TemplateInfobox Planet. --> 433 Eros (ˈɪərɒs irr'-os) is the first discovered Near-Earth asteroid More recently very precise measurements have been carried out by radar and by telemetry from space probes. Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships Telemetry (synonymous with Telematics) is a Technology that allows the remote measurement and reporting of Information of interest to the system designer A space probe is a scientific Space exploration mission in which a Robotic spacecraft leaves the Gravity well of Earth and approaches the

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. The gravitational constant, denoted G, is a Physical constant involved in the calculation of the gravitational attraction between objects with mass 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, calculations in celestial mechanics are typically performed in solar masses and astronomical units rather than in kilograms and kilometres. This approach makes all results dependent on the gravitational constant. A conversion to SI units would separate the results from the gravitational constant, at the cost of introducing additional uncertainty by assigning a specific value to that unknown constant.

Examples

The distances are approximate mean distances. It has to be taken into consideration that the distances between celestial bodies change in time due to their orbits and other factors. s are significant physical entities, associations or structures which current Science has confirmed to exist in Space. For other uses see Time (disambiguation Time is a component of a measuring system used to sequence events to compare the durations of In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star

Some conversion factors:

See also

References

  1. ^ Bureau International des Poids et Mesures (2006). The International Bureau of Weights and Measures ( Bureau international des poids et mesures, in French) is an international Standards organization, one The International System of Units (SI) (8th Edn). ISBN 92-822-2213-6.  p.  126. ,
  2. ^ IAU Website: Units

External links

Dictionary

astronomical unit

-noun

  1. (astronomy) The mean distance from the Earth to the Sun (the semi-major axis of Earth's orbit), approximately 149,600,000 kilometres (symbol AU), used to measure distances in the solar system.
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