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

A spectral line emitted by atoms undergoing energy transitions not normally allowed by the → selection rules of → quantum mechanics. Forbidden emission lines form in low-density interstellar gas and are collisionally excited. They are designated by enclosing in brackets, e.g. [O III] and [N II], O and N representing oxygen and nitrogen atoms respectively.

→ forbidden; → line.

A transition between two quantum mechanical → states that → violates the quantum mechanical → selection rules.

→ forbidden; → transition.

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."

1) The cause of a change in motion or shape of a body.
2) A → vector quantity defined by → Newton's second law as the rate of change of → momentum or, equivalently, as the product of → mass and → acceleration. A force is completely specified by giving its magnitude, direction, and point of application. In mechanics, force represents the quantitative measure of the mechanical interaction of material bodies.

From O.Fr. force, from L.L. fortia, from neut. pl. of L. fortis "strong," from forctus, from PIE base *bhergh- "high" (cf. Av. barəz- "high, mount," barezan- "height;" O.Pers. baršan- "height;" Mod.Pers. borz in (the mountain chain) Alborz, and borz "height, magnitude," bâlâ "up, above, high, elevated, height," Lori dialect berg "hill, mountain;" Skt. bhrant- "high;" O.E. burg, burh "castle, fortified place," from P.Gmc. *burgs "fortress;" Ger. Burg "castle," Goth. baurgs "city," E. burg, borough, Fr. bourgeois, bourgeoisie, faubourg).

Niru, from Mid.Pers. nêrok, Av. nairya- "manly, male" (cf. Skt. nárya-), from nar- "man, male" (Mid./Mod.Pers. nar- "male," Skt. nár- "male").

Same as → field of force.

→ force; → field.

One of the three quantities (k, α, and δ) which are used in the → radiation-driven wind theory to express the radiation pressure due to spectral lines. These coefficients parametrize the radiation acceleration as: g_rad≅ k(dv/dr)^αg_e, where g_e = σ_eL/4πcR_*² is the radiative acceleration by electron scattering. The parameter k is dependent on the number of lines that produce the radiation pressure. The parameter α depends on the optical depth of the driving lines and varies between 0 (optically thin) and 1 (optically thick). The parameter δ describes the dependence of k on the density with k ≅ ρ^δ. The velocity law of radiation-driven winds depends on α and δ, but not on k. The → mass loss rate depends on k, α, and δ (Castor et al. 1975, ApJ 195, 157; Lamers et al., 1995, ApJ 455, 269 and references therein).

→ force; → multiplier; → parameter.

Any set of forces acting on a → rigid body.

→ force; → system.

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.

1) Physics: Caused by an external force. → forced oscillation.
2) General: Subjected to force, compulsory.

Adjective from → force.

Adjective from zur, → strength.

A fluid flow generated when external forces cause the fluid to flow, for example when a flow is caused by a pump. It contrasts with → free flow.

→ forced; → flow.

The oscillation of a system or object induced by an external periodic force. See also → free oscillation.

→ forced; → oscillation.

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.

Loss of radiant energy received from an astronomical object due to the presence of absorbing matter situated between the object and observer.

→ foreground; → absorption.

1) A large tract of land covered with trees and underbrush; woodland (Dictionary.com).
2) In → graph theory, a → graph which contains no → cycles. The connected components of a forest are → trees.

M.E., from O.Fr. forest, probably from L.L. forestis (silva) "the outside woods," from L. foris "outside."

Jangal "a wood, forest, a vast land with plenty of trees;" cf. Skt. jangala- "arid , sparingly grown with trees and plants."

1) An instrument having two or more prongs or tines, for holding, lifting, etc., as an implement for handling food or any of various agricultural tools (dictionary.com).
2) Something resembling or suggesting this in form. → fork mounting.

Fork, from O.E. forca, from L. furca "pitchfork," of uncertain origin; → mounting.

Došâx, došâxé "two-pronged; fork," from do "two" (Mid.Pers. do, Av. dva-, Skt. dvi-, Gk. duo, L. duo, E. two, Ger. zwei, Fr. deux) + šâx "branch; horn," from Mid.Pers. šâk "branch;" cf. Lith. šaka "branch;" O.S. soxa "plough;" Gothic hoha "plough."
Cangâl "claws, fingers," from cang "claws, fingers," + -al, → -al.

A type of → equatorial mounting consisting of a two-pronged fork, which forms the → polar axis, with the → telescope pivoted between the prongs of the fork on a → declination axis.

→ fork; → mounting.

1) (n.) General: The shape and structure of something as distinguished from its material.
Philosophy: The structure, pattern, organization, or essential nature of anything. Structure or pattern as distinguished from matter.
Logic: The abstract relations of terms in a proposition, and of propositions to one another.
2) (v.intr.) of form.
3) (v.tr.) of form.

From O.Fr. forme, from L. forma "form, mold, shape, case," origin unknown.

1) Dis, disé "form, appearance," variants -diz, -diš (tandis "body form, like a body; effigy;" mâhdis "moon-like;" šabdiz "night color; a horse of dark rusty color;" andiš- "to think, contemplate"), from Mid.Pers. dêsag "form, appearance," dêsidan "to form, build;" Av. daēs- "to show," daēsa- "sign, omen;" cf. Skt. deś- "to show, point out;" PIE *deik- "to show" (cf. Gk. deiknumi "to show," dike "manner, custom;" L. dicere "to utter, say;" O.H.G. zeigon, Ger. zeigen "to show;" O.E. teon "to accuse," tæcan "to teach").
2) and 3) corresponding infintives of dis, as above.

1) According to, or following established or prescribed forms, conventions, etc.
2) Math., logic: Of a proof, in strict logical form with a justification for every step.
3) Math., logic: Of a calculation, correct in form; made with strict justification for every step; of or pertaining to manipulation of symbols without regard to their meaning.
4) → formal language.
5) → formal logic.

M.E. formal, formel, from L. formalis, from → form + → -al.

Diseyi, desevar, from dis, → form, + adj. suffixes -i and -var.

A language designed for use in situations in which natural language is unsuitable, as for example in → mathematics, → logic, or → computer  → programming. The symbols and formulas of such languages stand in precisely specified syntactic and semantic relations to one another (Dictionary.com).

→ formal; → language.