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

A → meteor that is brighter than the brightest planets, i.e. with an apparent magnitude of -5 or greater. Fireballs are often followed by → meteorite falls. Also called → bolide.

From → fire + ball, from O.E., from O.N. bollr "ball," from P.Gmc. *balluz (cf. O.H.G. ballo, Ger. Ball), from PIE base *bhel- "to swell."

Tašguy, from taš "fire," variant of âtaš→ fire + guy "ball, sphere," variants golulé, gullé, goruk, gulu, gudé (cf. Skt. guda- "ball, mouthful, lump, tumour," Pali gula- "ball," Gk. gloutos "rump," L. glomus "ball," globus "globe," Ger. Kugel, E. clot; PIE *gel- "to make into a ball").

A first object in → hydrostatic equilibrium predicted to form during early dynamical contraction of a → molecular cloud → clump in the course of the → first collapse.

→ first; → core.

A equation in which the highest → exponent of the → variable is 1. Same as → linear equation.

→ first; → degree; → equation.

The → dredge-up occurring after core hydrogen burning as the core contracts before helium burning ignites (on the ascending giant branch). The hydrogen envelope becomes convective and this convective zone penetrates deep into the core dredging up material that has been processed by the central nuclear reactions. As a result the abundances of helium and nitrogen are boosted.

→ first; → dredge-up.

A → differential equation containing only the first → derivative. For example, dy/dx = 3x and 2y(dy/dx) + 3x = 5.

→ first; → order; → differential; → equation.

Same as → first-order logic.

→ first; → order; → predicate; → calculus.

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) 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."

The action of bending or curving, or the condition of being bent or curved.

→ flex + suffix -ure.

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.

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.

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).

A decrease in the Galactic cosmic flux around sunspot maximum as a consequence of Solar flare activity. When sunspots explode, they often hurl massive clouds of hot gas away from the Sun, a phenomenon called → coronal mass ejections (CME). The CMEs contain not only gas but also magnetic fields. So when a CME sweeps past Earth, it also sweeps away many of the electrically-charged cosmic rays.

After Scott E. Forbush, American physicist who studied cosmic rays in the 1930s and 40s; → effect; decrease, from O.Fr. stem of descreistre, from L. decrescere, from → de- "away from" + crescere "to grow."

Kâheš, verbal noun of kâstan, kâhidan "to decrease," from Mid.Pers. kâhitan, kâstan, kâhênitan "to decrease, diminish, lessen;" Av. kasu- "small, little" (Mod.Pers. keh), Proto-Iranian *kas- "to be small, diminish, lessen."

The condition in a plasma when the → Lorentz force is zero, that is when the electric current flows along the magnetic field. Force-free magnetic fields are encountered in astrophysical plasmas with negligible gas pressure. The solar corona is the best available example of such fields in action in a plasma.

→ force; → free; → magnetic; → field.

The part of the arm between the → elbow and the → wrist.

From fore- a prefix meaning "before; front; superior," related to → per-; → arm.

Araš, variant ârenj "elbow;" Mid.Pers. âranj; O.Pers. arašan- "cubit;" Av. arəθnâ- "elbow;" Skt. aratni- "elbow," Iranian stem aratan-, araθn-, borrowed from Iranian into General Slavic as aršin "ell."

The ground or parts situated, or represented as situated, in the front; the portion of a scene or stellar field nearest to the viewer. → background.

From fore, from O.E. fore (prep.) "before, in front of;" (adv.) "before, previously" (cf. O.H.G. fora, Ger. vor, Goth. faiura); from PIE *per-/*pr- (cf. Skt. pura "before, formerly;" Av. paro "before;" Hittite para- "on, forth;" Gk. paros "before," para "from beside, beyond," peri "around, about, toward," pro "before;" L. pro "before, for, instead of," prae "before," per "through, for") + ground, from M.E., from O.E. grund; akin to O.H.G. grunt "ground."

Pišzaminé, from piš- "before; in front," from Mid.Pers. pêš "before, earlier;" O.Pers. paišiya "before; in the presence of" + ziminé "ground," from zamin "earth, ground" → earth.