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

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.

The ratio of the → focal length of a reflecting surface or lens to its effective diameter, i.e. to its → aperture. The smaller the focal ratio, the smaller the image scale and the more luminous the image for a given aperture.

→ focal; → ratio.

An optical component or system for changing the image scale of a telescope to achieve a better match between the → seeing disk and the → pixel size.

→ focal; → reducer.

1) (n.) A point where parallel light rays from an object are gathered together by a lens or a concave mirror. It is the place where the clearest image of a distant object forms. Also called focal point. See also → focal distance.
2) (v.) To adjust the eyepiece or objective of a telescope so that the image is clearly seen by the observer.

From L. focus "hearth, fireplace," of unknown origin,

Kânun "hearth, fireplace."

Of an optical system, being in focus or brought into focus; adjusted to produce a clear image.

Past participle of → focus.

The act of bringing into focus.

Noun of → focus.

A mass or layer of suspended water droplets or ice crystals near the surface of the earth, reducing visibility.

From Dan. fog "spray, shower, snowdrift," related to O.N. fok "snow flurry."

Meh "fog" (variants miq, mož, Tabari miyâ, Lori/Laki (kara) mozy, Ossetic mig/megæ), from Mid.Pers. mēq "cloud, mist," Av. mēγa- "cloud;" cf. Skt. meghá- "cloud, overcast weather;" Gk. omikhle "mist;" Lith. miglà "mist, haze;" PIE base *mighlā- "cloud."

A large, faintly colored, circular arc formed by light (usually sunlight) falling on cloud or fog. Also called → cloudbow.

→ fog; → bow.

A modified form of → Boltzmann's equation allowing for collision terms in an approximate way. It describes the rate of change of a particle's velocity as a result of small-angle collisional deflections.

After Dutch physicist Adriaan Fokker (1887-1972) and the German physicist Max Planck (1858-1947); → equation.

1) Usually, folks. (used with a plural verb) people in general.
2) (used with a plural verb) people as the carriers of culture, especially as representing the composite of social mores, customs, forms of behavior, etc., in a society (Dictionary.com).

M.E.; O.E. folc; cognate with O.Sax., O.Norse folk, O.H.G. folk (Ger. Volk).

Palg, from (Pashto) parrk "group of people," with variants: (Dehxodâ) parré "group of people; a circular disposition of troops for hunting or other purposes; a rank or file of soldiers;" (Lori, Torbart-Heydariye-yi, Qomi) borr "group of people, crowd;" (Qomi) borré; (Laki) berr "group of people;" (Qâyeni) bor "group, flock, herd;" (Kurd. Kurmanji) âpora "crowd;" transformation of -r- into -l- (as por = bol, → poly-) in Tabari bəlik, əllik "herd, flock;" ultimately from Proto-Ir. *paraka-, from *par- "to fill;" cf. Av. pər- "to fill, stuff with," pouru- "full, much, many;" O.Pers. paru- "much, many;" Pers. anbâr "ricks, storehouse," por, bol "full, much, many;" PIE *pel- "to fill;" → population.

The traditional beliefs, legends, customs, etc., of a people; lore of a people (Dictionary.com).

Coined by English scholar and antiquary William John Thoms (1803-1885), from → folk, + lore "traditional knowledge or belief," from M.E., O.E. lar cognate with Du. leer, Ger. Lehre "teaching," E. learn.

Palgvâr, literally "customs of people," from palg, → folk, + vâr "custom, rule, law" (Dehxodâ).