# An Etymological Dictionary of Astronomy and AstrophysicsEnglish-French-Persian

## فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

### M. Heydari-Malayeri    -    Paris Observatory

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 tidal force   نیروی ِ کشندی   niru-ye kešandi (#)Fr.: force de marée   The → gravitational force exerted on an extended body as a result of the difference in the strength of gravity between near and far parts of the body. The ocean tides on Earth result from the varying gravitational force of the Moon exerted on the Earth's oceans closest and farthest from the Moon. Tidal force, which is the → gradient of the gravitational force, varies as 1/r3. More specifically, Ftidal = dF/dr = (2GMm)/r3, where M is mass of the → primary body, m is mass of the → secondary body, r is distance between objects, and G the → gravitational constant. The total tidal force experienced across a body is equal to the tidal force (force per unit distance) multiplied by the diameter of that body: Ftt = Ftidal x 2R (provided that radius R is much smaller than r). It is obvious that the tidal force experienced by Earth at Moon's → perigee is larger than that at the → apogee. If the tidal force is stronger than a body's cohesiveness, the body will be disrupted. The minimum distance that a secondary comes to a primary before it is shattered by tidal force is called its → Roche limit. Tidal forces create → tidal heating.→ tidal; → force. tidal friction   مالش ِ کشندی   mâleš-e kešandiFr.: friction de marées   The → friction exerted on a → primary body (Earth) because of the → phase lag between the → tides and the → gravitational attraction of the → secondary body (Moon). The Earth's → rotation is faster than the Moon's orbital motion; therefore the Earth's → tidal bulges lead the Moon on its orbit. This has two important effects: The Earth is being pulled slightly "back" from its sense of rotation. So the Earth's rotation slows (by about 1 second every 50,000 years). Moreover, the Moon is being pulled slightly "forward" on its orbit. So it is harder for the Earth to hold it in place, and it moves further away from the Earth (by about 3-4 cm per yr). Tidal friction tends to synchronize the rotation period of a close-in companion with the period of its orbital motion around the primary. → tidal coupling.→ tidal; → friction. tidal heating   گرمش ِ کشندی   garmeš-e kešandiFr.: chauffage par marées   The heating of the → interior of a → planet or → satellite due to the → friction caused by → tidal forces. For example, the huge tidal forces by → Jupiter heat its close satellite → Io, making it a seismically very active body.→ tidal; → heating. tidal locking   قفل‌شد ِ کشندی   qoflšod-e kešandiFr.: verrouillage gravitationnel   The process whereby the → rotation period of a → primary body becomes identical to the → orbital period of a → secondary body. Tidal locking results from → tidal braking and leads to → synchronous rotation.→ tidal; → lock; → -ing. tidal radius   شعاع ِ کشندی   šo'â'-e kešandiFr.: rayon de marée   Same as → Roche limit.→ tidal; → radius. tidal stretching   درگش ِ کشندی   dargeš-e kešandiFr.: étirement de marée   The stretching of an object under → tidal force. Tidal stretching results from a difference in the gravitational pull felt on two sides of a body. It is proportional to the inverse cube of the distance to the source of gravity (1/r3). As a consequence, nearby objects, even small ones like the Moon, raise high tides, whereas distant giants like Jupiter do not produce much of an effect.→ tidal; → stretching. tidal stripping   لُختانش ِ کشندی   loxtâneš-e kešandiFr.: balayage par effet de marées   The phenomenon whereby gas and stars are ripped out from a gravitationally → bound system, such as a galaxy or → globular cluster, by the action of → tidal forces from an external, more massive object. See also → ram pressure stripping.→ tidal; → strip. tidal tail   دنباله‌ی ِ کشندی   donbâle-ye kešandiFr.: queue de marée   A long stream of stars and gas, often in the form of a spectacular tail, thrown off a galaxy when it collides with another galaxy. → interacting galaxies; → merger. Two tidal tails form in each galaxy, and they are more spectacular when the masses of the two galaxies are comparable, and when their relative orbit is in the same sense as the rotation inside each spiral galaxy.→ tidal; → tail. tidally locked   کشندانه قفل   kešandâné qoflFr.:   The description of a → system of two bodies undergoing → tidal locking.→ tidal; → -ly; → lock. tidally stripped   کشندانه لُختانیده   kešandâne loxtânideFr.: balayé par effet de marées   Describing a → stellar system that has undergone → tidal stripping.→ tidal; → -ly; → strip. tide   کشند   kešand (#)Fr.: marée   1) The periodic rising and falling of the waters of the ocean and its inlets. The tides result from the → gravitational attraction of the → Moon and → Sun acting upon the rotating → Earth. See also: → ebb tide, → high tide, → low tide, → neap tide, → spring tide, → tidal braking, → tidal bulge, → tidal capture, → tidal coupling, → tidal current, → tidal disruption, → tidal force, → tidal friction, → tidal heating, → tidal locking, → tidal radius, → tidal stretching. 2) → tidal force.M.E.; O.E. tid "time, hour" (cf. O.S. tid, Du. tijd, O.H.G. zit, Ger. Zeit "time").Kešand, from Mod./Mid.Pers. kešidan/kašidan "to draw, protract, trail, drag, carry," dialectal Yaqnavi xaš "to draw," Qomi xaš "streak, stria, mark," Lori kerr "line;" Av. karš- "to draw; to plow," karša- "furrow;" Proto-Iranian *kerš-/*xrah- "to draw, plow;" cf. Skt. kars-, kársati "to pull, drag, plow;" Gk. pelo, pelomai "to move, to bustle;" PIE base kwels- "to plow." tight   تنگ   tang (#)Fr.: serré   Firmly or closely fixed in place. → compact.M.E. thight, from O.N. thettr "watertight, close in texture, solid" (cf. second element in O.E. metethiht "stout from eating;" M.H.G. dihte "dense, thick," Ger. dicht "dense, tight," O.H.G. gidigan, Ger. gediegen "genuine, solid, worthy"), from PIE base *tenk- "to become firm, curdle, thicken;" cf. Ir. techt "curdled, coagulated," Lith. tankus "close, tight;" cognate with Pers. tang "tight," as below.Tang "tight; narrow, straight; tight," also "horse girth, a strap for fastening a load" (Mid.Pers. tang "tight, narrow"), tanjidan "to squeeze, press, pull together;" cf. Skt. tanákti "draws together, contracts;" cognate with E. tight, as above; PIE base *tenk- "to become firm, curdle, thicken." tight star cluster   خوشه‌ی ِ ستاره‌ای ِ تنگ   xuše-ye setâreyi-ye tangFr.: amas stellaire serré   A cluster of stars in which members are closely situated so that high resolution observations are required to distinguish them individually.→ tight; → star cluster. tightly bound binary star system   راژمان ِ ستاره‌ای ِ درین ِ تنگ بندیده   râžmân-e setâre-yi-ye dorin-e tang bandideFr.: système d'étoiles binaire très lié   → tight; → bound system; → binary star. tilt   گرا   gerâFr.: inclinaison   Optics: A deviation in the propagation direction of a beam of light. Tilt quantizes the average slope in both the X and Y directions of a → wavefront or phase profile across the pupil of an optical system.M.E. tylten "to upset, tumble," from tealt "unsteady" (cf. O.N. tyllast "to trip," Swed. tulta "to waddle," Norw. tylta "to walk on tip-toe," M.Du. touteren "to swing").Gerâ, present stem of gerâyidan "to incline toward; to intend; to make for." Gerâ may be a variant of Mod.Pers. kil "bent, inclined" (k/g and l/r interchanges), from PIE base *klei- "to lean, incline," cognate with L. clinare "to bend" (E. declination, inclination, etc.), Gk. klinein "to cause to slope, slant, incline," Skt. sri- "to lean," O.Pers. θray-, Av. sray- "to lean," P.Gmc. *khlinen (Ger. lehnen, E. lean). tilt angle   زاویه‌ی ِ گرا   zâviye-ye gerâFr.: angle d'inclinaison   The angle a rocket makes with the vertical as it curves along its trajectory.→ tilt; → angle. time   زمان، گاه، وقت (وخت)، تامن   zamân (#), gâh (#), vaqt (vaxt) (#), tâmenFr.: temps   1) A non-spatial sequential relation in which events occur in apparently irreversible succession from the past through the present to the future. → time's arrow. 2) A limited period or interval, as between two successive events.M.E.; O.E. tima "limited space of time," from P.Gmc. *timon "time" (cf. O.N. timi "time," Swed. timme "an hour"), akin to L. tempus (genitive temporis) "time" (Fr. temps, Sp. tiempo, It. tempo); maybe related to Pers. Tabari tum, tomon, temen "time;" Aftari ton "time."Zamân "time," from Mid.Pers. zamân, jamân "time," zamânak "period, epoch;" loaned into Aramaic and Ar., loaned into Arm. žam, žamanak "time;" prefixed Sogdian nγm "time, moment, hour;" Proto-Iranian *gām- "to go, to come;" cf. Av. gam- "to come; to go," jamaiti "goes;" O.Pers. gam- "to come; to go;" Mod./Mid.Pers. gâm "step, pace," âmadan "to come;" cf. Skt. gamati "goes;" Gk. bainein "to go, walk, step;" L. venire "to come;" Tocharian A käm- "to come;" O.H.G. queman "to come;" E. come; PIE base *gwem- "to go, come." Gâh "time; place;" Mid.Pers. gâh, gâs "time;" O.Pers. gāθu-; Av. gātav-, gātu- "place, throne, spot;" cf. Skt. gâtu- "going, motion; free space for moving; place of abode;" PIE *gwem- "to go, come." Vaqt, pronounced vaxt (وخت), but written vaqt (وقت), is a Pers. word meaning "portion (of time)". Its variants and related words in Mod./Mid.Pers. are: baxt "what is allotted, fate, fortune," baxš "portion, part, division," baxšidan, baxtan "to divide, distribute, grant," Av. base bag- "to attribute, allot, distribute," baxš- "to apportion, divide, give to," baxta- "what is allotted (luck, fortune)," baxədra- "part, portion," baγa- "master, god," O.Pers. bāji- "tribute, tax," cf. Skt. bhaj- "to share, divide, distribute, apportion," bhájati "divides," bhakta- "allotted; occupied with; a share; food or a meal, time of eating?," Gk. phagein "to eat (to have a share of food)"; PIE base *bhag- "to share out, apportion." Tâmen "time," from Tabari temen, tumun, tum "time," pərtəmən "long time;" Lori temen "age, length of life;" Aftari ton; Lâri, Garâši taim "time span" (related to L. tempus?). time allocation   تسک ِ زمان، ~ وقت   tesk-e zamân, ~ vaqtFr.: attribution de temps de télescope   The assignment of telescope time by an expert panel to proposals after evaluating the merits of the observation projects.→ time; → allocation. time constant   پایای ِ زمانی   pâyâ-ye zamâniFr.: constante de temps   Th speed of response of a detector, usually measured as 1/(2πν), where ν is the chopping frequency at which the responsivity fails to 1/√2 of its maximum value.→ time; → constant. time delay   درنگ   derang (#)Fr.: retard   1) The amount of time required for a → signal to travel from one point to another in an → electric circuit. 2) → gravitational lensing time delay.→ time; → delay.