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

In photography, an instrument used to measure the intensity of light from a scene to be photographed and to indicate the camera lens and shutter settings required to expose the film correctly.

→ exposure; → meter.

The length of time during which the receiver is irradiated.

→ exposure; → time.

1) To transform ideas into words; utter or state.
2) Math: To → transform into equivalent → terms. For example by → expanding or → factorizing an → expression. See also → suppress, → impress.

M.E. expressen, O.Fr. espresser "to press, squeeze out; speak one's mind," M.L. expressare, frequentative of exprimere "represent, describe," literally "to press out," from → ex- "out" + pressare "to press, push," from L. premere "to press, hold fast, cover, compress."

Zohâvidan, from zo- variant of os- "out," → ex-, + hâv, from Av. hau- "to press, squeeze out;" cf. Mid.Pers. hunîdan "to express, extract (juice)," hâwan "mortar;" akin to Skt. sav- "to press, press out;" O.H.G. sou, O.E. sēaw "juice;" + -idan infinitive suffix.

1) The act or an instance of expressing.
2) Math.: A statement using mathematical quantities such as → scalars, → variables, → parameters, → functions, and → sets, as well as → relational and → logical  → operators such as → equality, → conjunction, → existence, → union, etc. (Steven. G. Krantz, ed., Dictionary of Algebra, Arithmetic, and Trigonometry, 2001).

→ express; → -tion.

To stretch out; draw out to the full length; to enlarge the scope of; to increase the length or duration of.

From O.Fr. estendre, from L. extendere "stretch out," from → ex- "out" + tendere "to stretch," see below.

Ostanidan, from os-, → ex- + tanidan as in Av. ustāna- "stretched out" (ustāna-zasta- "with outstretched hands"), cf. Skt. uttāná- "stretched out, spread out." Mod.Pers. tanidan "to spin, twist, weave;" Mid.Pers. tanitan, from Av. tan- to stretch, extend;" cf. Skt. tan- to stretch, extend," tanoti "stretches," tantram "loom;" Gk. teinein "to stretch, pull tight;" L. tendere "to stretch;" PIE base *ten- "to stretch."

An object whose angular size exceeds the resolution of the instrument used to observe it.

→ extended; → object.

In radio astronomy, a source whose angular extent could be measured, as distinguished from a point source.

→ extended; → source.

1) An act or instance of extending; the state of being extended.
2) Physics: That property of a body by which it occupies space.
3) Math.: A field F is said to be an extension of a field K if K is a subfield of F.
4) Logic: The sum of all individuals or objects to which the comprehension of a term is applied. For example, the extension of the term "dog" is the set of all (past, present and future) dogs in the world.

Verbal noun of → extend.

The range over which a thing extends; length, area, volume, or scope.

→ extension.

1) Outer; being on the outer side; situated or being outside, which is outside.
2) Outside; an exterior part or surface.

From L. exterior "outward, outer, exterior," comparative of exterus "on the outside, outward, outer, foreign," itself a comparative of → ex- "out of."

Boruni, from borun, variant of birun "out, the outside," → out.

1) Any of the four angles that do not include a region of the space between two lines intersected by a third straight line (→ transversal).
2) The angle between any side and an extension of an adjacent side of a polygon.

→ exterior; → angle.

Of or pertaining to the outside or outer part.

M.E., from M.Fr. externe or directly from L. externus "outside, outward," from exterus, a comparative of → ex-, + → -al.

Biruni, adj. from birun "out, the outside," → out.

The → photoelectric effect in solids where free electrons are emitted from the surface of a substance (e.g., → semiconductor) when radiation of appropriate frequency falls on it. Also called → photoemissive effect.

→ external; → photoelectric; → effect.

The work done by a thermodynamic system as it expands against its surrounding environment. It is equal to ∫pdV, where p is the applied external pressure and V the volume, integrated from the initial V₁ to final V₂.

→ external; → work.

Verbal noun of → externalize.

→ externalize + → -tion.

1) To make external; embody in an outward form.
2) To regard or treat as being caused by externals; attribute to external causes (Dictionary.com).

→ external + → -ize.

1) Dimming of light by an intervening medium (the Earth's atmosphere or the interstellar medium). It is usually due to both scattering and absorption.
2) Paleontology: The act or process of dying out or coming to an end, becoming extinct: the extinction of a species; → mass extinction.

Noun of extinct, from L. extinctus, p.p. of extinguere "to quench, wipe out," from → ex- "out" + stinguere "to quench," from PIE base *steig- "to prick, stick, pierce;" cf. Mod.Pers. tiz, tež, tig, tej, tij, tiq "sharp;" Av. tiγra- "pointed," tiγray- "arrow;" → deblur.

Xâmuši, noun of xâmuš "extinguished; silent," Mid.Pers. xâmôš "silent;" cf. Skt. amrs- "to bear patiently."

Gradient of apparent magnitude with air mass.

→ extinction; → coefficient.

In → photometric calibration, the correction for energy loss undergone by radiation due to the → atmospheric extinction. Extinction correction is done using → standard stars observed at different → airmasses.

→ extinction; → correction.

A graph representing the variation of the → interstellar extinction against → wavelength. Usually it displays the → normalized values of extinction as a function of (the → inverse) of the wavelength (in → microns). See, e.g., Sandage & Mathis, 1979, Ann. Rev. Astron. Astrophys. 17, 73.

→ extinction; → curve.