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

1) To reveal, make known, make visible.
2) In imaging, to subject, as to the action of light, or other electromagnetic radiations.

M.E. exposen, from O.Fr. exposer "lay open, set forth," from L. exponere "set forth, lay open, exhibit," with contamination from poser "to lay, place" (→ position). doublet of expound.

1) Osnehâdan, from os-, → ex-, + nehâdan "to put, place," → position.
2) nur dâdan, from nur, → light + dâdan "to give," Mid.Pers. dâdan "to give;" O.Pers./Av. dā- "to give, grant, yield," dadāiti "he gives;" cf. Skt. dadáti "he gives;" Gk. didomi "I give;" L. dare "to give, offer;" PIE base *do- "to give."

1) The act of setting forth information or a viewpoint.
2) Public exhibition or show.

Verbal noun of → expose.

1) The act of exposing; the fact or state of being exposed, → expose.
2) In optics, the total radiant energy incident on a surface per unit area. It is equal to the integral over time of the radiant flux density.

Verbal noun of → expose.

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.

An act or instance of extending; the state of being extended.
Physics: That property of a body by which it occupies space.
Math.: A filed F is said to be an extension of a field K if K is a subfield of F.

Verbal noun of → extend.

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.