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

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.

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.

Same as → Roche limit.

→ tidal; → radius.

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.

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.

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.

The description of a → system of two bodies undergoing → tidal locking.

→ tidal; → -ly; → lock.

Describing a → stellar system that has undergone → tidal stripping.

→ tidal; → -ly; → strip.

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 k^wels- "to plow."

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."

A cluster of stars in which members are closely situated so that high resolution observations are required to distinguish them individually.

→ tight; → star cluster.

→ close binary star.

→ tight; → bound system; → binary star.

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).

The angle a rocket makes with the vertical as it curves along its trajectory.

→ tilt; → angle.

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 *g^wem- "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?).

The assignment of telescope time by an expert panel to proposals after evaluating the merits of the observation projects.

→ time; → allocation.

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.

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.

A distance-like quantity derived from → gravitational lensing time delay. It is given by a combination of three angular diameter distances in a strong lens system: D_Δt = (1 + z_L)[D_A(EL)D_A(ES) / D_A(LS)], where z_L is the → redshift of the → gravitational lens, while D_A(EL), D_A(ES), and D_A(LS) are the angular diameter distances from the Earth to the lens, from the Earth to the source, and from the lens to the source, respectively. As each of the distance is proportional to the inverse of H₀, D_Δt is proportional to 1/H₀.

→ time; → delay; → distance.

A phenomenon related to special and general relativity.
1) In → special relativity, the apparent shortening of time that occurs at speeds approaching that of light. A clock moving relative to a stationary observer will appear to slow down by a factor √(1- v²/c²), where v is the velocity and c the speed of light. → twins paradox.
2) In → general relativity, a clock in a stronger gravitational field runs more slowly. The dilation factor is given by: √(1- 2GM/rc²), where G is the gravitational constant, M the mass of the object creating the gravitational field, r a radial coordinate of the observer, which is analogous to the classical distance from the center of the object, and c the speed of light.

→ time; dilation, verbal noun of dilate, from M.E. dilaten, from O.Fr. dilater, from L. dilatare "make wider, enlarge," from → dis- "apart" + latus "wide."

Farâxeš, → dilation; zamân, → time.