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

To propel something through the air in any way, especially by swinging the arm and releasing the object from the hand; → ejecter.

M.E. throwen, thrawen, "to twist, turn writhe" (cf. O.S. thraian, M.Du. dræyen, Du. draaien, O.H.G. draen, Ger. drehen "to turn, twist").

Andâxtan, andâz-, from Mid.Pers. handâxtan, handâz-; ultimately from Proto-Iranian *ham-tak-, from *ham- "together, with, same," → syn- + *tak- "to run, to flow;" cf. Av. tak- "to run, to flow," taciāp- "flowing water," tacinti (3pl.pers.act.) "to flow," tacar- "course," tacan "current, streaming;" Mod.Pers. tacidan, tâxtan, tâzidan "to run; to hasten; to assault," tajan name of a river (initially "flowing, streaming, stream"), tâzi "swift (greyhound)," tak "running, rush," from Mid.Pers. tâz-, tâxtan "to flow, to cause to walk," tc- "to flow, to walk," tag "running, attack," tâzig "swift, fast;" Khotanese ttajs- "to flow, to walk;" Skt. tak- to rush, to hurry," takti "runs;" O.Ir. tech- "to flow;" Lith. teketi "to walk, to flow;" O.C.S. tešti "to walk, to hurry;" Tokharian B cake "river;" PIE base *tek^w- "to run; to flow.

The force that is exerted by a rocket, propeller, or jet engine to propel an aircraft. It is directed forward along the axis of the engine. → drag; → lift.

M.E. thrusten, thrysten (v.); O.N. thrysta "to thrust, force."

Pišrâné, from piš "before; in front" (Mid.Pers. pêš "before, earlier," O.Pers. paišiya "before; in the presence of") + râné, from rândan "to push, drive, cause to go" (causative of raftan "to go, walk, proceed," present tense stem row-, Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- "to go; to attack").

A fourth magnitude star (V = 3.65), called also α Draconis, in the constellation → Draco. Despite its designation as Alpha (α), it is the seventh brightest star of the constellation. Thuban is a → giant star of → spectral type A0 III lying 310 → light-years away. It has an faint → companion in an orbit with a 51 day period. Thuban was the → pole star at about 2700 BC. Other designations: HR 5291, HD 123299, and SAO 16273.

Thuban, from Ar. Ath-thu'bân (الثعبان) "a large male snake; basilisk."

A soft, malleable, ductile, lustrous silver-white metal; symbol Tm. Atomic number 69; atomic weight 168.9342; melting point about 1,545°C; boiling point 1,947°C; specific gravity 9.3. Thulium was discovered in 1879 by the Swedish chemist Per Theodor Cleve in a sample of erbium mineral. It was first isolated by the American chemist Charles James in 1911.

From Thule, the earliest name for Scandinavia.

A loud rumbling sound emitted by rapidly expanding air along the path of the electrical discharge of lightning.

M.E. thonder, thunder, O.E. thunor, from P.Gmc. *thunraz (cf. O.Fris. thuner, M.Du. donre, Du. donder, O.H.G. donar, Ger. Donner "thunder"), cognate with Pers. tondar, as below.

Tondar; Mid.Pers. tndwr, Sogdian twntr; cf. Skt. stan- "to thunder, resound," tanyati "thunders, roars," tanyu- "thundering," stanatha- "thunder;" L. tonare "to thunder," tonitrus "thunder" (Fr. tonnerre); PIE base *(s)tene- "to resound, thunder."

A → storm of → thunder and → lightning. Thunderstorms are associated with → convective clouds (Cumulonimbus) and are often accompanied by → precipitation. They are usually short-lived and hit on only a small area.

→ thunder; → storm.

Tondar-tuf, tufân-e tondari, from tondar, → thunder + tuf stem of tufidan "to roar, to raise a tumult," tufân "storm, the roaring of the sea, the confused hum of men or animals." This Persian word may be related to Gk. typhon "whirlwind, mythical monster associated with tempests."

Anatomy: The inner of the two bones of the leg, that extend from the knee to the ankle and articulate with the femur and the talus; shinbone (Dictionary.com).

From L. tibia "shinbone," also "pipe, flute," of unknown origin.

Dorošt-ney, literally "large reed," from dorošt "large," → macro-, + ney "reed, pipe, flute."

1) A small dot, mark, check, or electronic signal, as used to mark off an item on a list, serve as a reminder, or call attention to something (Dictionary.com).
2) To mark with a tick or ticks (usually followed by off).

M.E. tek "little touch," akin to Du. tik "a touch, pat," M.H.G. zic.

Sof, sofidan, related to sufâr "the groove at the end part of an arrow," → nock, on the model of Fr. coche "notch, score."

Of, pertaining to, characterized by, or subject to → tides.
See also: → tidal braking, → tidal bulge, → tidal capture, → tidal coupling, → tidal disruption, → tidal disruption event (TDE), → tidal disruption flare, → tidal dwarf galaxy, → tidal force, → tidal friction, → tidal heating, → tidal locking, → tidal radius, → tidal stretching, → tidal tail.

A hybrid formation from → tide + Latin-derived suffix → -al.

Adj. from kašand, → tide.

The physical process that slows the → Earth's rotation rate due to → tidal friction. The → Earth rotates faster than the → Moon orbits the Earth (24 hours compared to 27 days). The → friction between the ocean and the solid Earth below drags the → tidal bulge ahead of the line joining the Earth and the Moon. The → gravitational attraction of the Moon on the bulge provides a braking action on the Earth and decelerates its rotation. Tidal braking lengthens the day by 0.002 seconds every century. Because the total → angular momentum of the → Earth-Moon system in conserved, the loss in the angular momentum of the Earth is compensated by the orbital angular momentum of the Moon. Hence, the Moon moves away from Earth at a rate of about 3 cm per year. This process must continue until Earth's → day and → month are equal, at which point the Moon will never seem to move in Earth's sky and Earth is said to be tidally locked to the Moon (→ tidal locking).

→ tidal; → braking.

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.

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.

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.

The water current brought about by the → tides.

→ tidal; → current.

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

→ tidal; → disruption.

The process in which a star is torn apart by the → tidal forces of a → supermassive black hole. About 50% of the star's mass is eventually → accreted by the → black hole, generating a flare, which, in extreme cases of very high (→ super-Eddington) mass → accretion rates, can result in a → relativistic jet. TDEs have been proposed as sources of → ultra-high-energy cosmic rays and suggested as sources of high energy astrophysical → neutrinos (W. Winter and C. Lunardini, 2021, Nature Astronomy, arXiv:2005.06097 and references therein).

→ tidal; → disruption; → event.

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.

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.

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, F_tidal = 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: F_tt = F_tidal 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.

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.