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

1) An appropriate or favorable time or → occasion.
2) A situation or condition favorable for attainment of a goal (Dictionary.com).

→ opportune + → -ity.

1) To act against or provide resistance to.
2) To stand in the way of; hinder; obstruct (Dictionary.com).

M.E., from O.Fr. oposer "to oppose, resist; contradict," from poser "to place, lay down," blended with L. opponere "to oppose, to object," → position.

Pâdistidan, infinitive from pâdist, → opposition.

1) Situated, placed, or lying face to face with something else or each other, or in corresponding positions with relation to an intervening line, space, or thing: opposite ends of a room (Dictionary.com).
2) Contrary or radically different in some respect common to both, as in nature, qualities, direction, result, or significance; opposed (Dictionary.com).
3) An → antonym.

M.E., from M.Fr., from L. oppositus, p.p. of opponere, → opposition.

1) Ru-be-ru "face to face," → surface.
2) Pârun, short for pâdrun, from pâd-, → counter, + -run "side, direction" (as in birun, darun, vârun), → out.
3) Pâdcem, → antonym.

1) The action of opposing, resisting, or combating.
2) A person or group of people opposing, criticizing, or protesting something, someone, or another group (Dictionary.com).
3) The position of a solar system body having its orbit outside that of the Earth when the Earth is in a line between the Sun and the body. At opposition the body has a solar → elongation of 180°, and is closest to the Earth. It will, in principle, be visible throughout the night. It will rise in the east as the Sun sets in the west and it will set as the Sun rises. This is because, at opposition, the body and the Sun are 12 hours apart. The inner planets can never be in opposition. The opposite of opposition is → conjunction.
4) Two periodic quantities of the same frequency are said to be in opposition when the → phase difference between them is one half of a → period.

Verbal noun of → oppose.

Pâdist "standing against," from pâd- "agaist, contrary to," → anti-, + ist present stem of istâdan "to stand" (Mid.Pers. êstâtan, O.Pers./Av. sta- "to stand; to set;" Av. hištaiti; cf. Skt. sthâ- "to stand;" Gk. histemi "put, place, weigh," stasis "a standing still;" L. stare "to stand;" Lith. statau "place;" Goth. standan; PIE base *sta- "to set, stand").
Pâdistân, from pâdist + -ân suffix of place and time.

To burden with cruel or unjust impositions or restraints; subject to a burdensome or harsh exercise of authority or power (Dictionary.com).

M.E. oppressen, from O.Fr. opresser "oppress, torment, smother," from M.L. oppressare, from L. opprimere "press against, press together, press down; subdue, prosecute relentlessly," from op variant of ob "against" + premere "to press, hold fast."

Infinitive from setam, → oppression.

1) The exercise of authority or power in a burdensome, cruel, or unjust manner.
2) An act or instance of oppressing or subjecting to cruel or unjust impositions or restraints.
3) The state of being oppressed (Dictionary.com).

M.E. oppressioun, from O.Fr. opresser "oppress; torment," from M.L. oppressare, from L. opprimere "press against, press down;" from op, variant of ob "against" + premere "to press, hold fast."

Setam, from Mid.Pers. sthmbk / stambag / "oppressive; obstinate," related to sitabr "strong, firm," staft "hard; firm, strong; fierce," Pers. seft "firm, hard, tight;" sitanbah "strong, robust, bold;" Av. aša.stəmbana- "having the support/firmness of aša;" Lith stembti "to oppose;" Gk. astemphes "unshakable."

To make a choice; choose (usually followed by for).

From Fr. opter "to choose," from L. optare "to choose, desire, wish for," from L. optare "to desire, choose," from PIE root *op- "to choose, prefer."

Optidan, from L. optare, as above.

Of, relating to, or constituting a verbal mood that is expressive of wish or desire.

From M.Fr. optatif, from L. optativus, from optatus, p.p. of optare, → opt, + -ivus, → -ive.

Optâné, optmand, from opt present stem of optidan, → opt, + adj. suffixes -âné, -mand. -yi.

1) Of or pertaining to the eye or sight.
2) Same as → optical.

From M.Fr. optique, from M.L. opticus "of sight or seeing," from Gk. optikos "of or having to do with sight," from optos "seen, visible," from op-, root of opsesthai "be going to see," related to ops "eye," from PIE *ok^w- "eye/see."

1) Nuri, nurik, from nur, → light + -i, -ik adj. suffix → -ic.
2) Didgâni, related to didgân "eyes," plural of didé "eye; seen," from didan "to see" (Mid.Pers. ditan "to see, regard, catch sight of, contemplate, experience;" O.Pers. dī- "to see;" Av. dā(y)- "to see," didāti "sees;" cf. Skt. dhī- "to perceive, think, ponder; thought, reflection, meditation," dādhye; Gk. dedorka "have seen").

The direction in a doubly refracting crystal in which light is propagated without double refraction.

→ optic; → axis.

1) Of, pertaining to, or applying optics or the principles of optics.
2) Of or pertaining to sight or vision; visual; of or pertaining to the eye.

From → optic + → -al.

→ optic.

An imperfection in the imaging properties of a lens or mirror. The main aberrations are → chromatic aberration, → spherical aberration, → coma, → astigmatism, → field curvature, → distortion.

→ optical; → aberration.

The property possessed by some substances and their solutions of rotating the plane of vibration of → polarized light. When a beam of → linearly polarized light is sent through an optically active substance, such as crystalline quartz and sugar solution, the direction of vibration of the emerging linearly polarized light is found to be different from the original direction. Those which rotate the → plane of polarization to the right, for an observer looking in the incoming beam, are called → dextrorotatory or right handed; those which rotate it to the left, → levorotatory or left handed. Optical activity may be due to an asymmetry of molecules of a substance (solutions of cane sugar) or it may be a property of a crystal as a whole (crystalline quartz).

→ optical; → activity.

The mathematical evaluation of an optical system to determine its basic optical properties and image quality characteristics.

→ optical; → analysis.

An instrument used to test lenses by utilizing the → optical transfer function. It consists of a HeNe laser, a beamsplitter and two mirrors.

→ optical; → autocorrelator.

Line passing through the optical center and the center of curvature of a → spherical mirror or → lens. Same as → principal axis.

→ optical; → axis.

A track or table on which sources, lenses, mirrors, and other optical components can be mounted and moved. It is used in optics experiments.

→ optical; bench, M.E., from O.E. benc "long seat;" cf. Da. bænk, M.Du. banc, O.H.G. banch.

Miz "table," originally "preparations for entertaining a guest; guest;" Mid.Pers. mêzd "offering, meal;" nurik, nuršenâxti, → optical.

Of a thin lens, a point situated at the geometrical center of the lens, through which an incident ray passes without being deviated.

→ optical; → center.

Any device such as a → lens, → prism, → mirror, and/or other similar objects used in an → optical system.

→ optical; → component.

An astronomical object with usually weak emission in the → visible found to be the optical representation of the object radiating chiefly in other → wavelengths of the → electromagnetic spectrum.

→ optical; → counterpart.