An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 563
tidal bulge
  بر‌آمدگی ِ کشندی   
barâmadegi-ye kešandi

Fr.: bourrelet de marée   

Either of the two swells of land or water (on Earth) created by the pull of another object (Moon) orbiting around it. The → gravitational attraction between the → Earth and the → Moon is strongest on the side of the Earth that happens to be facing the Moon. This attraction causes the water on this "near side" of Earth to be pulled toward the Moon. As gravitational force acts to draw the water closer to the Moon, → inertia attempts to keep the water in place. But the gravitational force exceeds it and the water is pulled toward the Moon, causing a "bulge" of water on the near side toward the Moon. On the opposite side of the Earth, or the "far side," the gravitational attraction of the Moon is less because it is farther away. Here, inertia exceeds the gravitational force, and the water tries to keep going in a straight line, moving away from the Earth, also forming a bulge. In this way the combination of gravity and inertia creates two bulges of water (Ross, D.A. 1995. Introduction to Oceanography. New York, NY: Harper Collins. pp. 236-242).

tidal; → bulge.

tidal capture
  گیر‌افت ِ کشندی، گیر‌اندازی ِ ~   
gir-oft-e kešandi, gir-andâzi-ye ~

Fr.: capture par effet de marées   

A process in which two stars remain → bound after their → close encounter, leading to the formation of a → binary system. Tidal capture becomes possible when two stars pass each other so closely (within a few stellar radii) that their → tidal forces are able to absorb the excess energy of → unbound → orbital motion. The process was originally suggested by Fabian et al. (1975) to explain the origin of → low-mass X-ray binary systems observed for the first time in → globular clusters.

tidal; → capture.

tidal coupling
  جفسری ِ کشندی، جفتش ِ ~   
jafsari-ye kešandi, jofteš-e

Fr.: couplage par marées   

In a system composed of one celestial body orbiting another, the synchronization of the orbital and rotational motions of the two bodies under the action of → tidal forces. For example, Pluto is tidally coupled to its moon Charon. As for the → Earth-Moon system, billions of years from now, the Earth and the Moon will have the same period of rotation, and these will also exactly equal the orbital period of the Moon around the Earth. → tidal friction.

tidal; → coupling.

tidal current
  جریان ِ کشندی   
jarayân-e kešandi

Fr.: courant de marée   

The water current brought about by the → tides.

tidal; → current.

tidal disruption
  گسیخت ِ کشندی   
gosixt-e kešandi

Fr.: rupture par effet de marée   

The disruption of an extended astronomical object under the action of the → tidal forces exerted by another nearby object.

tidal; → disruption.

tidal disruption flare
  آلاو ِ گسیخت ِ کشندی   
âlâv-e gosixt-e kešandi

Fr.: éruption   

A luminosity enhancement in the → light curve of a galaxy observed in X-rays or ultraviolet surveys supposed to be associated with the → tidal disruption of a star that has passed close to a → supermassive black hole in the core of a → host galaxy. An → accretion disk forms after the tidal disruption. The flare event marks the beginning of the accretion process onto the black hole.

tidal; → disruption; → flare.

tidal dwarf galaxy
  کهکشان ِ کوتوله‌ی ِ کشندی   
kahkešân-e kutule-ye kešandi

Fr.: naine de marée   

A self-gravitating entity which has been formed from tidal material expelled during interactions between larger galaxies. TDGs are typically found at the tip of tidal tails at distances between 20 and 100 kpc from the merging galaxies, of which at least one should be a gas-rich galaxy. They are gas-rich objects that can be as massive as the Magellanic Clouds, form stars at a rate which might be as high as in blue compact dwarf galaxies and seem dynamically independent from their parent galaxies.

tidal; → dwarf; → galaxy.

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 kešandi

Fr.: 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 kešandi

Fr.: 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 kešandi

Fr.: 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 kešandi

Fr.: rayon de marée   

Same as → Roche limit.

tidal; → radius.

tidal stretching
  درگش ِ کشندی   
dargeš-e kešandi

Fr.: 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 tail
  دنباله‌ی ِ کشندی   
donbâle-ye kešandi

Fr.: 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 qofl


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

tidal; → -ly; → lock.

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."

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 tang

Fr.: 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.


Fr.: 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 gerâ

Fr.: angle d'inclinaison   

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

tilt; → angle.

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