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

The ability of a substance to flow; reciprocal of → viscosity.

→ fluid + → -ity.

A type of → luminescence in which photons of lower energy are emitted as the result of absorption of energy by an atom or molecule from other radiation. The phenomenon lasts as long as the stimulus responsible for it is present.

Coined by English mathematician and physicist Sir George G. Stokes (1819-1903) from fluor-, from → fluorspar, + → -escence, a suffix of nouns denoting action or process, change, state or condition, etc.

Possessing the property of → fluorescence.

→ fluorescence; → -escent.

A tubular → electric discharge lamp in which light is produced by the → fluorescence → phosphors coating the inside of the tube.

→ fluorescent; → lamp.

A compound (salt of hydrofluoric acid) containing → fluorine.

→ fluorine; → -id.

Gaseous chemical element; symbol F. It is the most reactive of all chemical elements. It is a yellowish, corrosive gas, which reacts with most organic and inorganic substances. → Atomic number 9; → atomic weight 18.9984; → melting point -219.62 °C; → boiling point -188.14 °C; → density 1.696 grams per liter at STP; → valence -1. Fluorine and its compounds are used in producing uranium (from the → hexafluoride) and more than 100 commercial fluorochemicals, including many high-temperature plastics.

From L. fluere "flow, → flux," since fluorspar (CaF₂) was used as a flux in metallurgy because of its low melting point. It was discovered in hydrofluoric acid by the Swedish pharmacist and chemist Carl-Wilhelm Scheele in 1771 but it was not isolated until 1886 by the French pharmacist and chemist Ferdinand Moisson.

A → mineral composed of calcium fluoride, CaF₂, also called → fluorspar, that is often → fluorescent under → ultraviolet light.

From fluor-, → fluorine, + → -ite.

Same as → fluorite.

From fluor-, → fluorine, + spar "a crystalline mineral."

The amount of energy, fluid, or particles passing in a given direction in a unit of time.

O.Fr. flux, from L. fluxus, p.p. of fluere "to flow," PIE base *bhleug- (cf. L. flumen "river;" Gk. phluein "to boil over, bubble up," phlein "to abound").

Šâr "outpouring of water, wine, etc.," šâridan "to flow (as rivers), with a great noise; to pour," âbšâr "waterfall;" saršâr "overflowing; brim-full;" Ossetic ægzælyn "to pour down;" Pashto zγâstəl/zγâl- "to swim;" Av. γžār- "to flow;" cf. Skt. ksar- "to flow;" Gk. phtheirein "to destroy, perish."

The → calibration of the flux received by a detector in terms of absolute units.

→ flux; → calibration.

Flux of radiation that falls on a detector per unit surface area of the detector per unit bandwidth of the radiation per unit time.

→ flux; → density.

In radio astronomy, same as → jansky (symbol Jy), a unit of electromagnetic flux equivalent to 10^-26 watts per square meter per Hertz.

→ flux; → density.

In Newton's work on → calculus, the rate of change of a fluent (i.e. a flowing quantity), today commonly known as → variable. For a fluent x, the fluxion is denoted dx/dt. An obsolete mathematical term.

From L. → fluxion-, stem of fluere "to flow," → flux.

To move through the air using wings. Travel through the air or outer space.

M.E. flien, O.E. fleogan; cognate with O.H.G. fliogan, Ger. fliegen, O.Norse fljuga.

Infinitive from parvâz, → flight.

A trajectory that takes a → space probe close to a Solar System body (planet, satellite, asteroid, comet) but does not permit it to enter an orbit about the body.

→ fly + by, from M.E., from O.E. be or bi, from P.Gmc. *bi "around, about" (cf. Du. bij, Ger. bei "by, at, near"), from *umbi, (cf. L. ambi "around, about," Gk. amphi "around, about," Skt. abhi "on both sides," Av. aibi, aiwi, O.Pers. aiby "to, against, in addition to," Mid.Pers. aw-, ab-, Mod.Pers. af- (as in afzudan "to increase, add," afruxtan "to inflame, kindle, blaze," afqân "lamentation, groaning, cires for help").

Barvâz, from bar- "on, up; upon, over," → on-, + vâz, as in parvâz, → flight.

Of or relating to a focus; placed at or measured from a focus.

→ focus + → -al.

same as → focal length.

→ focal; → distance.

The distance between the optical center of a lens, or the surface of a mirror, and its focus.

→ focal; → distance.

A plane at right angles to the principal axis of a lens or mirror on which the best image is formed.

→ focal; → plane.

Same as → focus.

→ focal; → point.