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

The process or instance of adapting a mathematical curve to data points.

Verbal form of → fit.

The discrepancy between the mathematical curve and data points. → fit.

→ fitting; → error.

A cardinal number whose symbol is 5, V, or ۵.

Five, from O.E. fif, from P.Gmc. *fimfe (cf. O.S. fif, O.H.G. funf), from PIE *penk^we "five;" cognate with Pers. panj, as below.

Panj, from Mid.Pers. panj; Av. panca; cf. Skt. páñca; Gk. pente; L. quinque; E. five, as above.

A photometric system which uses five filters, from ultraviolet to the red part of the visual spectrum: U, B, V, R and I.

→ five; → color; → system.

The 500 m diameter → radio telescope which is the largest → single-dish antenna in the world. It is an Arecibo type telescope nestled within a natural basin in China's remote and mountainous Dawodang, Kedu Town, in southeastern China's Guizhou Province. The → reflector consists of 4,450 triangular panels, each with a side length of 11 m. More than 2,000 → actuators are used, according to the feedback from the measuring system, to deform the whole reflector surface and directly correct for → spherical aberration. Several detectors are used to cover a frequency range of 70 MHz to 3 GHz.

→ five; → hundred; → meter; → aperture; → spherical; → radio; → telescope.

1) To make fast, firm, or stable.
2) To place definitely and more or less permanently (Dictionary.com).

M.E. fixen, probably from O.Fr. fixe "fixed," from L. fixus "fixed, fast, established, settled," p.p. of figere "to fix, fasten."

Infinitive, from barjâ, → fixed.

The act of fixing or the state of being fixed.

Verbal noun of → fix; → -tion.

1) Fastened, attached, or placed so as to be firm and not readily movable; firmly implanted; stationary; rigid.
2) Rendered stable or permanent, as color.
3) Set or intent upon something; steadily directed (Dictionary.com).

Past participle from → fix.

Barjâ "fixed; in place; properly placed," from bar "on, upon, up," → object, + jâ, → place,

A → heavenly body that, in → contrast to the → planets, does not appear to change its relative → position on the → celestial sphere.

Fixed, p.p. of → fix; → star.

Setâré, → star; barjâ, → fixed.
Istâdé (Biruni in at-Tafhim) "standing," from istâdan "to stand;" O.Pers./Av. sta- "to stand, stand still; set" (cf. Skt. sthâ- "to stand;" Gk. histemi "put, place, weigh;" stasis "a standing still;" Lith. statau "place;" Goth. standan; L. stare "to stand;" PIE base *sta- "to stand");
Biyâbâni (Biruni in at-Tafhim), from Mid.Pers. awiyâbânig "fixed," from negation prefix → a- + wiyâbânig "wandering," from wiyâbân "deluded, seduced," wiyâbânênidan "to lead astray, deceive," from Av. vi- "apart, away from, out" (O.Pers. viy- "apart, away;" cf. Skt. vi- "apart, asunder, away, out;" L. vitare "to avoid, turn aside") + dab- "to deceive;" cf. Skt. vimugdha- "confused, bewildered," vimohita- "confused, infatuated." Note that biyâbân "desert" is from an other origin.

The determination of the shape of an optical surface by means of → interferometry using a → fringe pattern formed with respect to a reference surface.

Named after the French physicist Armand Hippolyte Louis Fizeau (1819-1896), see also → toothed-wheel experiment; → test.

1) Burning gas or vapor, as from wood or coal, that is undergoing combustion; a portion of ignited gas or vapor.
2) Any flame-like condition; glow; inflamed condition (Dictionary.com).

M.E. flaume, variant of flaumbe from Anglo-French flaume, flaumbe "a flame;" O.Fr. flambe, from L. flammula "small flame," diminutive of flamma "flame, blazing fire," from PIE *bhleg- "to shine, flash," from root *bhel- (1) "to shine, flash, burn."

Âyež, from (Dehxodâ) âyež "flame," variants âyiž, âyežé, ižak, of unknown origin.

A stellar designation system in which each star is assigned a number followed by the Latin genitive of its corresponding → constellation, such as → 61 Cygni and 82 Eridani. Compare with the → Bayer designation.

Named after John Flamsteed (1646-1719), founder of the Greenwich Observatory, and the first astronomer royal of England, who introduced this system in his catalog Historia Coelestis Britannica (1725); → designation.

1) A sudden blaze or burst of fire or light.
2) → solar flare.

From v. flare "to spread out," said of hair, a ship's sides, etc., of unknown origin.

Âlâv, "blaze, fire," variants alow, Borujerdi elew "fire," Garkuyeyi alôv "flame," Hamadâni elow "flame," Lori alô "flame," Tabari aluk "flame, spark," Torbat-Heydariyeyi alow "flame;" cf. Gk. aithos "fire," aitho "to kindle;" Skt. edh- "to set alight, kindle," édha-, édhas- "firewood;" Av. aēsma- "firewood;" Mod.Pers. hizom, himé "firewood;" PIE base *aidh- "to burn," *aidhos- "fire."

A member of a class of dwarf stars that undergoes sudden, intense outbursts of light (mean amplitude about 0.5-0.6 mag).

→ flare; → star.

A model of → accretion disk around a → pre-main sequence star or a → protostar in which the ratio of the disk thickness to the distance from the star increases outward. Current models of the irradiation of flared disks by stellar radiation predict that a central hole is created around the young star due to the evaporation of dust by the stellar radiation. The inner rim of the disk, at 0.5 to 1 AU from the star, is irradiated by the star "frontally" (at 90° angle). The heat produced by the irradiation causes the inner rim to puff up. A part of the disk, from about 1 to 6 AU, lies in the shadow of the puffed-up inner rim. The surface layers in this region do not receive stellar photons directly. Therefore, there is no significant heating of the disk midplane by reprocessed stellar flux from the disk surface. The midplane temperatures in the shadowed part of the disk are governed by the → near infrared emission of the inner rim, scattering of stellar light by dust particles outside the disk plane, and radial diffusion which exchanges energy between adjacent slabs. As for the outer parts of the disk, the surface is irradiated by the central star thanks to the outward widening of the disk. These parts remain flared, because the absorbed stellar flux is partially emitted toward the midplane, keeping the internal temperatures high enough to push the surface layers up. The flattened-disk model explains the observed → spectral energy distribution of some objects such as HD 179218. It also accounts for the observed strong → far-infrared, → excess, strong → PAH emission, and strong [O I] emission. Compare with → self-shadowed disk. See also → protoplanetary disk.

Flared, from flare "to spread gradually outward, as the end of a trumpet, having a gradual increase in width," of unknown origin; → disk.

Gerdé, → disk; borun-gošâ "opening outward," from borun "out, the outside" (Mid.Pers. bêron, from bê "outside, out, away" + rôn "side, direction;" Av. ravan- "(course of a) river") + gošâ stem of gošâdan, gošudan "to open;" Mid.Pers. wišâdan "to open, let free;" Khotanese hiyā "bound;" O.Pers. višta "untied, loosend;" vištāspa- (personal name) "with loosened horses;" Av. višta "untied," hita- "fastened, tied on;" cf. Skt. sā- "to bind, fasten," syáti "binds."

A Sudden, brief burst of light. In particular, → green flash.

From M.E. flasshen "to sprinkle, splash," from flasken, probably imitative.

Deraxš, present stem of deraxšidan "to shine, radiate," from raxš "lightening, reflection of light," raxšidan "to shine, flash," O.Pers. raucah-, Av. raocah- "light" (cf. Skt. roka- "brightness, light," Gk. leukos "white, clear," L. lux "light" (also lumen, luna), E. light, Ger. Licht, Fr. lumière; PIE base *leuk- "light, brightness"); cognate with Mod.Pers. words ruz "day," rowšan "bright, clear," foruq "light," and afruxtan "to light, kindle."

The spectrum of the solar → chromosphere obtained during a → solar eclipse in the instant before or after → totality. In the flash spectrum the usual solar → absorption lines are replaced with bright → emission lines. This is because in that very short interval only the → photosphere is eclipsed by the Moon, and not the chromosphere. The American astronomer Charles A. Young was the first to observe it during the the solar eclipse of 1870 (December 22) in Spain.

The flash designation comes from the fact that the change from dark-line to bright-line spectrum is very rapid; → flash; → spectrum.

Level and horizontal, without any slope; even and smooth, without any bumps or hollows.
See also:
→ flat manifold, → flat Universe, → flat-field, → flatness problem.

Flat, from O.N. flatr, from P.Gmc. *flataz (cf. O.H.G. flaz "flat, level," O.E. flet, O.H.G. flezzi "floor"), perhaps from PIE *pla- (cf. Gk. platys "broad, flat;" Av. pərətu- "broad, wide;" Skt. prthu- "broad, wide, large").

Taxt "flat;" Mid.Pers. taxtag "tablet, plank, (chess)board."

A manifold with a → Riemannian metric that has → zero → curvature.

→ flat; → manifold.

A galactic → rotation curve in which the → rotation velocity is constant in the outer parts. The flat component is preceded by a rising curve that shows solid body rotation in the very center of the → galaxy. A flat rotation curve implies that the mass is still increasing linearly with radius. See also → dark matter.

→ flat; → rotation; → curve.