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

A basic rule in → group theory stating that there exists a unit group element e, called the identity, such that for any element a of the group a * e = e * a = a.

→ identity; → axiom.

In a mathematical system, an element which leaves unchanged any other element on which it operates. Thus 0 is the identity element for addition: a + 0 = a. And 1 is the identity element for multiplication: a . 1 = a.

→ identity; → element.

Math.: Any function f for which f(x) = x for all x in the domain of definition.

→ identity; → function.

In linear algebra, the simplest nontrivial diagonal matrix, an n-by-n square matrix with ones on the main diagonal and zeros elsewhere.

→ identity; → matrix.

An operator which takes a real number to the same real number.

→ identity; → operator.

(Conjunction) in case that; granting or supposing that; on condition that. → if and only if.

M.E., from O.E. gif; akin to O.H.G. ibu "if."

Agar "if," from Mid.Pers. agar, hakar "if;" O.Pers. ha-karam "once;" from ha- "one," variant ham-, → com- (cf. Av. ha-; Skt. sa-; Gk. ha-; L. sem-; PIE *sem- "one"), + karam- "a time," maybe from kar- "to do; doing," → work; cf. Av. hakərət "once;" Skt. sakrt "once;" Gk. hapaks "once;" L. semel "once."

Logic, Math.: An → expression indicating that two → statements so connected are → necessary and sufficient conditions for one another. The corresponding logical symbols usually used are: ↔, ⇔, ≡, and iff.

→ if; → and; → only.

A → rock formed by the solidification of molten material that originated within the Earth (as → magma or → lava).

Igneous, from L. igneus "of fire, fiery," from ignis "fire," from PIE *egni- (cf. Skt. agni- "fire, sacrificial fire," O.C.S. ogni, Lith. ugnis "fire"); → rock.

Sang "stone, rock," → stone; âzarin "fiery," from âzar, variants âtaš, taš, from Mid.Pers. âtaxš, âtur "fire;" Av. ātar-, āθr- "fire," singular nominative ātarš-; O.Pers. ātar- "fire;" Av. āθaurvan- "fire priest;" Skt. átharvan- "fire priest;" cf. L. ater "black" ("blackened by fire"); Arm. airem "burns;" Serb. vatra "fire;" PIE base *āter- "fire" + -in adj. suffix.

1) To set on fire.
2) To take fire, to begin to burn.

From L. ignitus, p.p. of ignire "to set fire," from ignis "fire, flame, light."

Girândan transitive form of gereftan "to take, catch" (Mid.Pers. griftan, Av./O.Pers. grab- "to take, seize," cf. Skt. grah-, grabh- "to seize, take," graha "seizing, holding, perceiving," M.L.G. grabben "to grab," from P.Gmc. *grab, E. grab "to take or grasp suddenly;" PIE base *ghrebh- "to seize").

1) The act or fact of igniting; state of being ignited.
2) The process of setting something on fire.

Verbal noun of → ignite.

The minimum temperature to which a fuel must be heated in order to initiate self sustained combustion independent of another heat source.

→ ignition; → temperature.

A → generalized coordinate that does not appear explicitly in the → Lagrangian function. Also called → cyclic coordinate. Ignorable coordinates do not participate in the → Legendre transformation, and are also absent from the → Hamiltonian function. The generalized → momentum associated with an ignorable coordinate is a → constant of the motion.

→ ignore; → coordinate.

To set aside, e.g. → ignorable coordinate.

From Fr. ignorer, from L. ignorare "not to know, disregard," from ignarus "not knowing, unaware," from in- "not," → un-, + gnarus "aware, acquainted with," related to gnoscere "to → know".

Nâdidé engâštan literally "supposed not seen," from nâdidé "not seen" (from nâ- "not," → un- + didé "seen," p.p. of didan "to see," → sight) + engâštan "to suppose" (→ hypothesis).

Optics: Intensity of → illumination.
The amount of visible light incident per unit area of surface per second; measured in lux (lumens per unit square meter). → irradiance.

Rowšanâyi, → illumination; tanuyi→ intensity.

General: An act or instance of illuminating. The fact or condition of being illuminated.

Illumination, from O.Fr. illumination, from L. illuminationem (nom. illuminatio), from illuminare "to throw into light," from → in- "in" + lumen "light," cognate with Pers. rowšan, as below.

Rowšanâyi, noun of quality and state from rowšan "bright, clear," related to ruz "day," foruq "light," and afruxtan "to light, kindle," rowzané "window, aperture;" Mid.Pers. rôšn "light; bright, luminous," rôc "day," rocânak "window;" O.Pers. raucah-, Av. raocana- "bright, shining, radiant," raocah- "light, luminous; daylight;" akin to Skt. rocaná- "bright, shining," roka- "brightness, light;" Gk. leukos "white, clear;" L. lux "light," also lumen "light, window," luna "Moon;" E. light; Ger. Licht; Fr. lumière; PIE base *leuk- "light, brightness."

1) A false sense impression of something actually present.
2) Something that produces a false or misleading impression of reality. → optical illusion.
3) An instance of being deceived.

From O.Fr. illusion "a mocking," from L. illusionem (nom. illusio) "a mocking, irony," from illudere "to mock at," literally "to play with," from in- "at" + ludere "to play," from ludus "a game, play;" PIE base *leid- "to play, jest."

Safmân, literally "wrong thought, ~ idea," from saf "wrong" (Tâleši), → false, + mân "thought," → idea.

1) In an optical system, the point to which light rays are converged (real image) or from which they appear to diverge (virtual image) after reflection or refraction.
Math.: A number, point, or unique element of a space that corresponds to some other number, point, or unit element.
2) To make an image of; to picture or represent in the mind.

From O.Fr. image, from L. imaginem (nom. imago) "copy, picture, likeness " from stem of imitari "to copy, imitate," from im-, stem of imitare "to copy, imitate" + -ago noun suffix.

1) Vine, from (Sorani) Kurd. vina or vena "image, picture; similar," from vin/ven, variant of bin, present stem of dîtin, Pers. didan "to see, to look;" cf. Taleshi vinde "to see," Tati vindiyan "to see," Persian bin-, didan "→ see." The relation between "image" and "see" is probably from the fact that the image of a subject can be seen without its presence.
Tasvir, loan from Ar.
2) Infinitive with gereftan "take," → take, and dâštan "to have, to hold," → property.

The process of adding several usually low-exposure images to create an image having a significantly higher signal/noise ratio.

→ image; → co-; → add.

A technique using a mathematical model of the blurring process to recover the original, sharp image. See also → blurred image.

→ image; → deburring.

The meeting of light rays emanating from an object after crossing an optical system.

→ image; → formation.