140 relations: Aberration of light, Agreement (linguistics), Ahmad ibn Muhammad ibn Kathir al-Farghani, Al-Battani, Al-Biruni, Albert A. Michelson, Albert Einstein, Angular frequency, Apollo program, Archimedes, Aristarchus of Samos, Arithmetic underflow, Arthur Robert Hinks, Astronomical constant, Astronomical system of units, Astronomy, Astronomy & Astrophysics, Barycentric Dynamical Time, Cayenne, Celestial mechanics, Celestial Mechanics and Dynamical Astronomy, Christiaan Huygens, Cleomedes, Cosmic distance ladder, Earth, Earth radius, Earth's orbit, Edmond Halley, Edwin Gifford, Ellipse, Elliptic orbit, Ephemeris, Eratosthenes, Eusebius, Floating-point arithmetic, Frame of reference, French Guiana, Galactic Center, Gaussian gravitational constant, General relativity, Gerald J. Toomer, Giovanni Domenico Cassini, Godefroy Wendelin, Gravitational constant, Harold Spencer Jones, Hipparchus, IAU (1976) System of Astronomical Constants, Imperial units, Inflection, Integer overflow, ..., International Astronomical Union, International Bureau of Weights and Measures, International Committee for Weights and Measures, International Earth Rotation and Reference Systems Service, International System of Units, ISO 80000-3, James Gregory (mathematician), Jérôme Lalande, Jean Picard, Jean Richer, Jeremiah Horrocks, Jet Propulsion Laboratory, Johannes Kepler, Julian year (astronomy), Kepler's laws of planetary motion, Kuiper belt, Length, Li (unit), Light-second, Light-year, Line segment, Lunar distance (astronomy), Lunar phase, Mars, Mercury (planet), Metre, Metric system, Metric tensor (general relativity), Mile, Milky Way, Minute and second of arc, Monthly Notices of the Royal Astronomical Society, Myriad, NASA, Near-Earth object, Nicolaus Copernicus, Noel Swerdlow, Non-SI units mentioned in the SI, Numerical model of the Solar System, Ole Rømer, On the Sizes and Distances (Aristarchus), Oort cloud, Orders of magnitude (length), Pappus of Alexandria, Parallax, Paris, Parsec, Perihelion and aphelion, Photon, Posidonius, Praeparatio evangelica, Proper length, Proxima Centauri, Ptolemy, Radar, Rudolphine Tables, Russian Academy of Sciences, Secular variation, Semi-major and semi-minor axes, Seven Years' War, Simon Newcomb, Solar mass, Solar radius, Solar System, Space probe, Speed of light, Stadion (unit), Standard gravitational parameter, Star system, Sun, Sunlight, Telemetry, Telescope, Terrestrial Time, The Astrophysical Journal, The Sand Reckoner, Theory of relativity, Toise, Transit of Venus, Transit of Venus, 1639, Truncation, Tycho Brahe, Unit of length, United Kingdom Hydrographic Office, United States customary units, United States Naval Observatory, Venus, Zhoubi Suanjing, Zij, 433 Eros. Expand index (90 more) »

## Aberration of light

The aberration of light (also referred to as astronomical aberration, stellar aberration, or velocity aberration) is an astronomical phenomenon which produces an apparent motion of celestial objects about their true positions, dependent on the velocity of the observer.

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## Agreement (linguistics)

Agreement or concord (abbreviated) happens when a word changes form depending on the other words to which it relates.

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## Ahmad ibn Muhammad ibn Kathir al-Farghani

. (800/805-870) also known as Alfraganus in the West, was a Persian astronomer in the Abbasid court in Baghdad, and one of the most famous astronomers in the 9th century.

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## Al-Battani

Abū ʿAbd Allāh Muḥammad ibn Jābir ibn Sinān al-Raqqī al-Ḥarrānī aṣ-Ṣābiʾ al-Battānī (Arabic: محمد بن جابر بن سنان البتاني) (Latinized as Albategnius, Albategni or Albatenius) (c. 858 – 929) was an Arab astronomer, astrologer, and mathematician.

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## Al-Biruni

Abū Rayḥān Muḥammad ibn Aḥmad Al-Bīrūnī (Chorasmian/ابوریحان بیرونی Abū Rayḥān Bērōnī; New Persian: Abū Rayḥān Bīrūnī) (973–1050), known as Al-Biruni (البيروني) in English, was an IranianD.J. Boilot, "Al-Biruni (Beruni), Abu'l Rayhan Muhammad b. Ahmad", in Encyclopaedia of Islam (Leiden), New Ed., vol.1:1236–1238.

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## Albert A. Michelson

Albert Abraham Michelson FFRS HFRSE (December 19, 1852 – May 9, 1931) was an American physicist known for his work on measuring the speed of light and especially for the Michelson–Morley experiment.

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## Albert Einstein

Albert Einstein (14 March 1879 – 18 April 1955) was a German-born theoretical physicist who developed the theory of relativity, one of the two pillars of modern physics (alongside quantum mechanics).

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## Angular frequency

In physics, angular frequency ω (also referred to by the terms angular speed, radial frequency, circular frequency, orbital frequency, radian frequency, and pulsatance) is a scalar measure of rotation rate.

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## Apollo program

The Apollo program, also known as Project Apollo, was the third United States human spaceflight program carried out by the National Aeronautics and Space Administration (NASA), which accomplished landing the first humans on the Moon from 1969 to 1972.

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## Archimedes

Archimedes of Syracuse (Ἀρχιμήδης) was a Greek mathematician, physicist, engineer, inventor, and astronomer.

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## Aristarchus of Samos

Aristarchus of Samos (Ἀρίσταρχος ὁ Σάμιος, Aristarkhos ho Samios; c. 310 – c. 230 BC) was an ancient Greek astronomer and mathematician who presented the first known model that placed the Sun at the center of the known universe with the Earth revolving around it (see Solar system).

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## Arithmetic underflow

The term arithmetic underflow (or "floating point underflow", or just "underflow") is a condition in a computer program where the result of a calculation is a number of smaller absolute value than the computer can actually represent in memory on its CPU.

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## Arthur Robert Hinks

Arthur Robert Hinks, CBE, FRS (26 May 1873 – 14 April 1945) was a British astronomer and geographer.

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## Astronomical constant

An astronomical constant is a physical constant used in astronomy.

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## Astronomical system of units

The astronomical system of units, formally called the IAU (1976) System of Astronomical Constants, is a system of measurement developed for use in astronomy.

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## Astronomy

Astronomy (from ἀστρονομία) is a natural science that studies celestial objects and phenomena.

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## Astronomy & Astrophysics

Astronomy & Astrophysics is a peer-reviewed scientific journal covering theoretical, observational, and instrumental astronomy and astrophysics.

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## Barycentric Dynamical Time

Barycentric Dynamical Time (TDB, from the French Temps Dynamique Barycentrique) is a relativistic coordinate time scale, intended for astronomical use as a time standard to take account of time dilation when calculating orbits and astronomical ephemerides of planets, asteroids, comets and interplanetary spacecraft in the Solar System.

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## Cayenne

Cayenne is the capital city of French Guiana, an overseas region and department of France located in South America.

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## Celestial mechanics

Celestial mechanics is the branch of astronomy that deals with the motions of celestial objects.

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## Celestial Mechanics and Dynamical Astronomy

Celestial Mechanics and Dynamical Astronomy is a scientific journal covering the fields of astronomy and astrophysics.

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## Christiaan Huygens

Christiaan Huygens (Hugenius; 14 April 1629 – 8 July 1695) was a Dutch physicist, mathematician, astronomer and inventor, who is widely regarded as one of the greatest scientists of all time and a major figure in the scientific revolution.

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## Cleomedes

Cleomedes (Κλεομήδης) was a Greek astronomer who is known chiefly for his book On the Circular Motions of the Celestial Bodies (Κυκλικὴ θεωρία μετεώρων).

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## Cosmic distance ladder

The cosmic distance ladder (also known as the extragalactic distance scale) is the succession of methods by which astronomers determine the distances to celestial objects.

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## Earth

Earth is the third planet from the Sun and the only astronomical object known to harbor life.

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## Earth radius

Earth radius is the approximate distance from Earth's center to its surface, about.

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## Earth's orbit

Earth's orbit is the trajectory along which Earth travels around the Sun.

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## Edmond Halley

Edmond (or Edmund) Halley, FRS (–) was an English astronomer, geophysicist, mathematician, meteorologist, and physicist.

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## Edwin Gifford

Edwin Hamilton Gifford, DD (18 December 1820 – 4 May 1905) was an eminent Anglican priest and author in the second half of the 19th century.

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## Ellipse

In mathematics, an ellipse is a curve in a plane surrounding two focal points such that the sum of the distances to the two focal points is constant for every point on the curve.

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## Elliptic orbit

In astrodynamics or celestial mechanics, an elliptic orbit or elliptical orbit is a Kepler orbit with an eccentricity of less than 1; this includes the special case of a circular orbit, with eccentricity equal to 0.

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## Ephemeris

In astronomy and celestial navigation, an ephemeris (plural: ephemerides) gives the positions of naturally occurring astronomical objects as well as artificial satellites in the sky at a given time or times.

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## Eratosthenes

Eratosthenes of Cyrene (Ἐρατοσθένης ὁ Κυρηναῖος,; –) was a Greek mathematician, geographer, poet, astronomer, and music theorist.

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## Eusebius

Eusebius of Caesarea (Εὐσέβιος τῆς Καισαρείας, Eusébios tés Kaisareías; 260/265 – 339/340), also known as Eusebius Pamphili (from the Εὐσέβιος τοῦ Παμϕίλου), was a historian of Christianity, exegete, and Christian polemicist. He became the bishop of Caesarea Maritima about 314 AD. Together with Pamphilus, he was a scholar of the Biblical canon and is regarded as an extremely learned Christian of his time. He wrote Demonstrations of the Gospel, Preparations for the Gospel, and On Discrepancies between the Gospels, studies of the Biblical text. As "Father of Church History" (not to be confused with the title of Church Father), he produced the Ecclesiastical History, On the Life of Pamphilus, the Chronicle and On the Martyrs. During the Council of Antiochia (325) he was excommunicated for subscribing to the heresy of Arius, and thus withdrawn during the First Council of Nicaea where he accepted that the Homoousion referred to the Logos. Never recognized as a Saint, he became counselor of Constantine the Great, and with the bishop of Nicomedia he continued to polemicize against Saint Athanasius of Alexandria, Church Fathers, since he was condemned in the First Council of Tyre in 335.

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## Floating-point arithmetic

In computing, floating-point arithmetic is arithmetic using formulaic representation of real numbers as an approximation so as to support a trade-off between range and precision.

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## Frame of reference

In physics, a frame of reference (or reference frame) consists of an abstract coordinate system and the set of physical reference points that uniquely fix (locate and orient) the coordinate system and standardize measurements.

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## French Guiana

French Guiana (pronounced or, Guyane), officially called Guiana (Guyane), is an overseas department and region of France, on the north Atlantic coast of South America in the Guyanas.

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## Galactic Center

The Galactic Center is the rotational center of the Milky Way.

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## Gaussian gravitational constant

The Gaussian gravitational constant (symbol) is a parameter used in the orbital mechanics of the solar system.

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## General relativity

General relativity (GR, also known as the general theory of relativity or GTR) is the geometric theory of gravitation published by Albert Einstein in 1915 and the current description of gravitation in modern physics.

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## Gerald J. Toomer

Gerald James Toomer (born 23 November 1934) is a historian of astronomy and mathematics who has written numerous books and papers on ancient Greek and medieval Islamic astronomy.

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## Giovanni Domenico Cassini

Giovanni Domenico Cassini (8 June 1625 – 14 September 1712) was an Italian (naturalised French) mathematician, astronomer and engineer.

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## Godefroy Wendelin

Govaert Wendelen, Latinized Godefridus Wendelinus, or sometimes Vendelinus (6 June 1580 – 24 October 1667) was a Flemish astronomer.

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## Gravitational constant

The gravitational constant (also known as the "universal gravitational constant", the "Newtonian constant of gravitation", or the "Cavendish gravitational constant"), denoted by the letter, is an empirical physical constant involved in the calculation of gravitational effects in Sir Isaac Newton's law of universal gravitation and in Albert Einstein's general theory of relativity.

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## Harold Spencer Jones

Sir Harold Spencer Jones KBE FRS FRSE PRAS (29 March 1890 Kensington, London – 3 November 1960) was an English astronomer.

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## Hipparchus

Hipparchus of Nicaea (Ἵππαρχος, Hipparkhos) was a Greek astronomer, geographer, and mathematician.

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## IAU (1976) System of Astronomical Constants

The International Astronomical Union at its XVIth General Assembly in Grenoble in 1976, accepted (Resolution No. 1) a whole new consistent set of astronomical constants IAU(1976) ibidem: Commission 4 (Ephemerides) recommendations 1,2,3,5,6: pp.52..67 recommended for reduction of astronomical observations, and for computation of ephemerides.

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## Imperial units

The system of imperial units or the imperial system (also known as British Imperial or Exchequer Standards of 1825) is the system of units first defined in the British Weights and Measures Act of 1824, which was later refined and reduced.

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## Inflection

In grammar, inflection or inflexion – sometimes called accidence – is the modification of a word to express different grammatical categories such as tense, case, voice, aspect, person, number, gender, and mood.

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## Integer overflow

In computer programming, an integer overflow occurs when an arithmetic operation attempts to create a numeric value that is outside of the range that can be represented with a given number of bits – either larger than the maximum or lower than the minimum representable value.

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## International Astronomical Union

The International Astronomical Union (IAU; Union astronomique internationale, UAI) is an international association of professional astronomers, at the PhD level and beyond, active in professional research and education in astronomy.

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## International Bureau of Weights and Measures

The International Bureau of Weights and Measures (Bureau international des poids et mesures) is an intergovernmental organization established by the Metre Convention, through which Member States act together on matters related to measurement science and measurement standards.

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## International Committee for Weights and Measures

The International Committee for Weights and Measures (abbreviated CIPM from the French Comité international des poids et mesures) consists of eighteen persons, each of a different nationality, from Member States of the Metre Convention (Convention du Mètre) appointed by the General Conference on Weights and Measures (CGPM) whose principal task is to promote worldwide uniformity in units of measurement by taking direct action or by submitting proposals to the CGPM.

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## International Earth Rotation and Reference Systems Service

The International Earth Rotation and Reference Systems Service (IERS), formerly the International Earth Rotation Service, is the body responsible for maintaining global time and reference frame standards, notably through its Earth Orientation Parameter (EOP) and International Celestial Reference System (ICRS) groups.

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## International System of Units

The International System of Units (SI, abbreviated from the French Système international (d'unités)) is the modern form of the metric system, and is the most widely used system of measurement.

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## ISO 80000-3

ISO 80000-3:2006 is an ISO standard entitled Quantities and units – Part 3: Space and time, superseding ISO 31-1 and ISO 31-2.

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## James Gregory (mathematician)

James Gregory FRS (November 1638 – October 1675) was a Scottish mathematician and astronomer.

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## Jérôme Lalande

Joseph Jérôme Lefrançois de Lalande (11 July 1732 – 4 April 1807) was a French astronomer, freemason and writer.

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## Jean Picard

Jean-Félix Picard (21 July 1620 – 12 July 1682) was a French astronomer and priest born in La Flèche, where he studied at the Jesuit Collège Royal Henry-Le-Grand.

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## Jean Richer

Jean Richer (1630–1696) was a French astronomer and assistant (élève astronome) at The French Academy of Sciences, under the direction of Giovanni Domenico Cassini.

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## Jeremiah Horrocks

Jeremiah Horrocks (1618 – 3 January 1641), sometimes given as Jeremiah Horrox (the Latinised version that he used on the Emmanuel College register and in his Latin manuscripts), – See footnote 1 was an English astronomer.

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## Jet Propulsion Laboratory

The Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center in Pasadena, California, United States, with large portions of the campus in La Cañada Flintridge, California.

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## Johannes Kepler

Johannes Kepler (December 27, 1571 – November 15, 1630) was a German mathematician, astronomer, and astrologer.

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## Julian year (astronomy)

In astronomy, a Julian year (symbol: a) is a unit of measurement of time defined as exactly 365.25 days of SI seconds each.

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## Kepler's laws of planetary motion

In astronomy, Kepler's laws of planetary motion are three scientific laws describing the motion of planets around the Sun.

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## Kuiper belt

The Kuiper belt, occasionally called the Edgeworth–Kuiper belt, is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune (at 30 AU) to approximately 50 AU from the Sun.

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## Length

In geometric measurements, length is the most extended dimension of an object.

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## Li (unit)

The li (lǐ, or 市里, shìlǐ), also known as the Chinese mile, is a traditional Chinese unit of distance.

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## Light-second

The light-second is a unit of length useful in astronomy, telecommunications and relativistic physics.

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## Light-year

The light-year is a unit of length used to express astronomical distances and measures about 9.5 trillion kilometres or 5.9 trillion miles.

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## Line segment

In geometry, a line segment is a part of a line that is bounded by two distinct end points, and contains every point on the line between its endpoints.

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## Lunar distance (astronomy)

Lunar distance (LD or \Delta_), also called Earth–Moon distance, Earth–Moon characteristic distance, or distance to the Moon, is a unit of measure in astronomy.

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## Lunar phase

The lunar phase or phase of the Moon is the shape of the directly sunlit portion of the Moon as viewed from Earth.

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## Mars

Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System after Mercury.

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## Mercury (planet)

Mercury is the smallest and innermost planet in the Solar System.

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## Metre

The metre (British spelling and BIPM spelling) or meter (American spelling) (from the French unit mètre, from the Greek noun μέτρον, "measure") is the base unit of length in some metric systems, including the International System of Units (SI).

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## Metric system

The metric system is an internationally adopted decimal system of measurement.

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## Metric tensor (general relativity)

In general relativity, the metric tensor (in this context often abbreviated to simply the metric) is the fundamental object of study.

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## Mile

The mile is an English unit of length of linear measure equal to 5,280 feet, or 1,760 yards, and standardised as exactly 1,609.344 metres by international agreement in 1959.

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## Milky Way

The Milky Way is the galaxy that contains our Solar System.

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## Minute and second of arc

A minute of arc, arcminute (arcmin), arc minute, or minute arc is a unit of angular measurement equal to of one degree.

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## Monthly Notices of the Royal Astronomical Society

Monthly Notices of the Royal Astronomical Society (MNRAS) is a peer-reviewed scientific journal covering research in astronomy and astrophysics.

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## Myriad

A myriad (from Ancient Greek label) is technically the number ten thousand; in that sense, the term is used almost exclusively in translations from Greek, Latin, or Chinese, or when talking about ancient Greek numbers.

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## NASA

The National Aeronautics and Space Administration (NASA) is an independent agency of the executive branch of the United States federal government responsible for the civilian space program, as well as aeronautics and aerospace research.

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## Near-Earth object

A near-Earth object (NEO) is any small Solar System body whose orbit can bring it into proximity with Earth.

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## Nicolaus Copernicus

Nicolaus Copernicus (Mikołaj Kopernik; Nikolaus Kopernikus; Niklas Koppernigk; 19 February 1473 – 24 May 1543) was a Renaissance-era mathematician and astronomer who formulated a model of the universe that placed the Sun rather than the Earth at the center of the universe, likely independently of Aristarchus of Samos, who had formulated such a model some eighteen centuries earlier.

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## Noel Swerdlow

Noel Mark Swerdlow (born 1941) is a professor emeritus of history, astronomy and astrophysics at the University of Chicago.

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## Non-SI units mentioned in the SI

This is a list of units that are not defined as part of the International System of Units (SI), but are otherwise mentioned in the SI, because either the General Conference on Weights and Measures (CGPM) accepts their use as being multiples or submultiples of SI-units, they have important contemporary application worldwide, or are otherwise commonly encountered worldwide.

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## Numerical model of the Solar System

A numerical model of the Solar System is a set of mathematical equations, which, when solved, give the approximate positions of the planets as a function of time.

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## Ole Rømer

Ole Christensen Rømer (25 September 1644 – 19 September 1710) was a Danish astronomer who in 1676 made the first quantitative measurements of the speed of light.

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## On the Sizes and Distances (Aristarchus)

On the Sizes and Distances (of the Sun and Moon) (Περὶ μεγεθῶν καὶ ἀποστημάτων, Peri megethon kai apostematon) is widely accepted as the only extant work written by Aristarchus of Samos, an ancient Greek astronomer who lived circa 310–230 BCE.

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## Oort cloud

The Oort cloud, named after the Dutch astronomer Jan Oort, sometimes called the Öpik–Oort cloud, is a theoretical cloud of predominantly icy planetesimals proposed to surround the Sun at distances ranging from.

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## Orders of magnitude (length)

The following are examples of orders of magnitude for different lengths.

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## Pappus of Alexandria

Pappus of Alexandria (Πάππος ὁ Ἀλεξανδρεύς; c. 290 – c. 350 AD) was one of the last great Greek mathematicians of Antiquity, known for his Synagoge (Συναγωγή) or Collection (c. 340), and for Pappus's hexagon theorem in projective geometry.

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## Parallax

Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines.

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## Paris

Paris is the capital and most populous city of France, with an area of and a population of 2,206,488.

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## Parsec

The parsec (symbol: pc) is a unit of length used to measure large distances to astronomical objects outside the Solar System.

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## Perihelion and aphelion

The perihelion of any orbit of a celestial body about the Sun is the point where the body comes nearest to the Sun.

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## Photon

The photon is a type of elementary particle, the quantum of the electromagnetic field including electromagnetic radiation such as light, and the force carrier for the electromagnetic force (even when static via virtual particles).

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## Posidonius

Posidonius (Ποσειδώνιος, Poseidonios, meaning "of Poseidon") "of Apameia" (ὁ Ἀπαμεύς) or "of Rhodes" (ὁ Ῥόδιος) (c. 135 BCE – c. 51 BCE), was a Greek Stoic philosopher, politician, astronomer, geographer, historian and teacher native to Apamea, Syria.

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## Praeparatio evangelica

Preparation for the Gospel (Εὐαγγελικὴ προπαρασκευή), commonly known by its Latin title Praeparatio evangelica, was a work of Christian apologetics written by Eusebius in the early part of the fourth century AD.

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## Proper length

Proper length or rest length refers to the length of an object in the object's rest frame.

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## Proxima Centauri

Proxima Centauri, or Alpha Centauri C, is a red dwarf, a small low-mass star, about from the Sun in the constellation of Centaurus.

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## Ptolemy

Claudius Ptolemy (Κλαύδιος Πτολεμαῖος, Klaúdios Ptolemaîos; Claudius Ptolemaeus) was a Greco-Roman mathematician, astronomer, geographer, astrologer, and poet of a single epigram in the Greek Anthology.

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## Radar

Radar is an object-detection system that uses radio waves to determine the range, angle, or velocity of objects.

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## Rudolphine Tables

The Rudolphine Tables (Tabulae Rudolphinae) consist of a star catalogue and planetary tables published by Johannes Kepler in 1627, using some observational data collected by Tycho Brahe (1546–1601).

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## Russian Academy of Sciences

The Russian Academy of Sciences (RAS; Росси́йская акаде́мия нау́к (РАН) Rossíiskaya akadémiya naúk) consists of the national academy of Russia; a network of scientific research institutes from across the Russian Federation; and additional scientific and social units such as libraries, publishing units, and hospitals.

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## Secular variation

The secular variation of a time series is its long-term non-periodic variation (see Decomposition of time series).

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## Semi-major and semi-minor axes

In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the widest points of the perimeter.

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## Seven Years' War

The Seven Years' War was a global conflict fought between 1756 and 1763.

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## Simon Newcomb

Simon Newcomb (March 12, 1835 – July 11, 1909) was a Canadian–American astronomer, applied mathematician and autodidactic polymath, who was Professor of Mathematics in the U.S. Navy and at Johns Hopkins.

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## Solar mass

The solar mass is a standard unit of mass in astronomy, equal to approximately.

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## Solar radius

Solar radius is a unit of distance used to express the size of stars in astronomy.

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## Solar System

The Solar SystemCapitalization of the name varies.

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## Space probe

A space probe is a robotic spacecraft that does not orbit the Earth, but, instead, explores further into outer space.

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## Speed of light

The speed of light in vacuum, commonly denoted, is a universal physical constant important in many areas of physics.

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## Stadion (unit)

The stadion (στάδιον; stadium), formerly also anglicized as stade, was an ancient Greek unit of length, based on the length of a typical sports stadium of the time.

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## Standard gravitational parameter

In celestial mechanics, the standard gravitational parameter μ of a celestial body is the product of the gravitational constant G and the mass M of the body.

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## Star system

A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction.

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## Sun

The Sun is the star at the center of the Solar System.

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## Sunlight

Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light.

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## Telemetry

Telemetry is an automated communications process by which measurements and other data are collected at remote or inaccessible points and transmitted to receiving equipment for monitoring.

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## Telescope

A telescope is an optical instrument that aids in the observation of remote objects by collecting electromagnetic radiation (such as visible light).

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## Terrestrial Time

Terrestrial Time (TT) is a modern astronomical time standard defined by the International Astronomical Union, primarily for time-measurements of astronomical observations made from the surface of Earth.

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## The Astrophysical Journal

The Astrophysical Journal, often abbreviated ApJ (pronounced "ap jay") in references and speech, is a peer-reviewed scientific journal of astrophysics and astronomy, established in 1895 by American astronomers George Ellery Hale and James Edward Keeler.

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## The Sand Reckoner

The Sand Reckoner (Ψαμμίτης, Psammites) is a work by Archimedes in which he set out to determine an upper bound for the number of grains of sand that fit into the universe.

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## Theory of relativity

The theory of relativity usually encompasses two interrelated theories by Albert Einstein: special relativity and general relativity.

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## Toise

A toise (symbol: T) is a unit of measure for length, area and volume originating in pre-revolutionary France.

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## Transit of Venus

A transit of Venus across the Sun takes place when the planet Venus passes directly between the Sun and a superior planet, becoming visible against (and hence obscuring a small portion of) the solar disk.

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## Transit of Venus, 1639

The first known observations and recording of a transit of Venus were made in 1639 by the English astronomers Jeremiah Horrocks and his friend and correspondent William Crabtree.

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## Truncation

In mathematics and computer science, truncation is limiting the number of digits right of the decimal point.

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## Tycho Brahe

Tycho Brahe (born Tyge Ottesen Brahe;. He adopted the Latinized form "Tycho Brahe" (sometimes written Tÿcho) at around age fifteen. The name Tycho comes from Tyche (Τύχη, meaning "luck" in Greek, Roman equivalent: Fortuna), a tutelary deity of fortune and prosperity of ancient Greek city cults. He is now generally referred to as "Tycho," as was common in Scandinavia in his time, rather than by his surname "Brahe" (a spurious appellative form of his name, Tycho de Brahe, only appears much later). 14 December 154624 October 1601) was a Danish nobleman, astronomer, and writer known for his accurate and comprehensive astronomical and planetary observations.

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## Unit of length

A unit of length refers to any discrete, pre-established length or distance having a constant magnitude which is used as a reference or convention to express linear dimension.

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## United Kingdom Hydrographic Office

The United Kingdom Hydrographic Office (UKHO) is the UK's agency for providing hydrographic and marine geospatial data to mariners and maritime organisations across the world.

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## United States customary units

United States customary units are a system of measurements commonly used in the United States.

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## United States Naval Observatory

The United States Naval Observatory (USNO) is one of the oldest scientific agencies in the United States, with a primary mission to produce Positioning, Navigation and Timing (PNT) for the United States Navy and the United States Department of Defense.

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## Venus

Venus is the second planet from the Sun, orbiting it every 224.7 Earth days.

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## Zhoubi Suanjing

The Zhoubi Suanjing, or Chou Pei Suan Ching (周髀算经), is one of the oldest Chinese mathematical texts.

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## Zij

A zīj (زيج) is an Islamic astronomical book that tabulates parameters used for astronomical calculations of the positions of the Sun, Moon, stars, and planets.

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## 433 Eros

433 Eros, provisional designation, is a stony and elongated asteroid of the Amor group and the first discovered and second-largest near-Earth object with a mean-diameter of approximately 16.8 kilometers.

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## Redirects here:

AU (astronomy), Astronomical Unit, Astronomical Units, Astronomical units, Distance from the earth to the sun, Distance to the Sun, Solar unit, ㍳.

## References

[1] https://en.wikipedia.org/wiki/Astronomical_unit