An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

→ advance of perihelion, → relativistic precession.

→ apsidal; → precession.

The astronomical activities that took place from the 8th to the 14th century in the Middle East, Central Asia, North Africa, and Moorish Spain. Arab/Arabic is not meant as an ethnic but rather a linguistic term. In fact a large number of Non-Arab scholars, mainly Persians, Mongols, and Spanish people, wrote their works in Arabic. Even so, many astronomical works were also produced in the other languages of this civilization, especially Persian and in the later centuries Turkish. For example, the main → zijs were originally written in Persian, a notable example being the Zij of Ulugh Beg (c. A.D. 1394-1449), a landmark in precise observations before the Renaissance. Therefore, the term Arabic astronomy is misleading. It also creates a disparity with respect to Western scholars who wrote in Latin. The term "Latin astronomy" is meaningless and as far as these scholars are concerned, the Latin adjective is not specified. For example, the expressions like "the Latin astronomer Copernicus," "the Latin physicist Newton," or "the Latin philosopher Leibniz" are not used. See also → Islamic astronomy.

M.E. arabik, from O.Fr. arabique, from L. Arabicus; → astronomy.

A constant quantity in → equations which takes various values but which remains unaffected by the changes in the values of the → variables of the equation. Most → differential equations have more than one → solution. In general, the number of arbitrary constants of an ordinary differential equation is given by the → order of the highest → derivative.

→ arbitrary; → constant.

The difference in → right ascension between the → Sun and the → Moon, measured in degrees.

→ arc; → separation.

The → angular  → difference in → altitude between the → Sun and the → Moon.

→ arc; → vision.

A unit of angular size equal to 1/3.600 of a degree.

→ arc; → second.

The study that deals with the astronomical knowledge of prehistoric peoples (season events, calendars, observing sites, astronomical alignments) and its influence on their cultures and societies (mythologies, religions, life). Archaeoastronomy covers the intersection between astronomy and archaeology. Same as → astroarchaeology, megalithic astronomy.

Archeoastronomy, from L. archaeo-, archeo "ancient; earlier; primitive," from Gk. arkhaio-, from arkhaios "ancient" + → astronomy.

Bâstânaxtaršenâsi, from bâstân "ancient" + axtaršenâsi, → astronomy.

An angular measurement equal to 1/3600 of a degree or 1/60 of an arcminute. It is denoted by the symbol ''. There are 206,264.5'' in a radian, so that 1'' = 4.848 × 10^-6 radians.

→ arc; → second.

A → chemical element which occurs as a colorless, odorless, and tasteless gas in the atmosphere (of which it constitutes 0.94% by volume) and in some volcanic gases; symbol Ar. → Atomic number 18; → atomic weight 39.948; → melting point -189.2°C; → boiling points -185.7°C.

Argon, from Gk. neutral of argos "inactive, idle, lazy," from negation prefix → a- + ergon "work," → energy. It was discovered in 1895 by the Scottish chemist William Ramsay and the English physicist Robert John Strutt (Lord Rayleigh) in liquified atmospheric air.

The angular distance between the → ascending node of an object orbiting the Sun and its perihelion. Argument of perihelion is measured in the → orbital plane with respect to the Sun and in the direction of motion. It is one of the → orbital elements and usually shown with the symbol ω. See also: → argument of perigee, → argument of periapsis.

→ argument; → perihelion.

The presentation and elaboration of an argument or arguments.

Noun from → argument.

A → sequence of n numbers or quantities such that the difference between any two successive terms is a constant. In particular, if a is the first term, the nth term is a + (n - 1)d, where d is the constant. Also called → arithmetic sequence.

→ arithmetic; → progression.

An important relationship in physical chemistry that combines the concepts of → activation energy and the → Maxwell-Boltzmann distribution law. It is expressed by: k = Ae^-E_a/(RT), where k is the chemical → reaction rate, E_a is the activation energy, R is the → gas constant, and T is → temperature.

Named for Svante Arrhenius (1859-1927), Swedish chemist and physicist who suggested the relationship in 1889.

A shallow flat vessel filled with → mercury or some other viscous → liquid used in special → sextant for measuring altitudes of celestial bodies at sea in the absence of a → visible horizon.

→ artificial; → horizon.

The act of ascending; ascent.

Verbal noun of → ascend; → -tion.

The act of asserting or something that is asserted.

→ assert; → -tion.

1) An appointment for a meeting.
2) The act of assigning; → assignment (Dictionary.com).

Verbal noun of → assign.

1) The act of associating, → associate; the state of being associated.
2) A group of → astronomical objects physically or apparently gathered in a particular area of sky, for example an → stellar association.
3) An organization of persons having a common interest. → dissociation.

Association, noun from → associate.

Âhazeš, verbal noun of → âhazidan→ associate. Anjoman, for the meaning 3, from Mid.Pers. anjaman, from Av. han-jamana, from han- "together" + jamana, from gam- "to come;" cf. Skt. samgamana "gathering together."

A celestial body making part of an astronomical association.

→ association; → member.

A fact or statement (as a proposition, axiom, postulate, or notion) taken for granted.

M.E., from L.L. assumption, assumptio "taking up," from L. assumere, → assume.

Âgarb, from â-, nuance prefix, + garb, from Av./O.Pers. grab-, Av. gərəb- "to take, to seize;" cf. Mod.Pers. gereftan "to take; to assume;" Skt. grah-, grabh- "to seize, to take," graha "seizing, holding, perceiving;" M.L.G. grabben "to grab;" E. grab "to take or grasp suddenly;" PIE *ghrebh- "to seize."
Ar. farz "assumption, hypothesis."