tidal disruption flare
âlâv-e gosixt-e kešandi
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 dwarf galaxy
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.
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.
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.
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.
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.
Fr.: rayon de marée
Same as → Roche limit.
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.
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.
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.
→ 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.
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."
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
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.
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).
Fr.: angle d'inclinaison
The angle a rocket makes with the vertical as it curves along its trajectory.
zamân (#), gâh (#), vaqt (vaxt) (#), tâmen
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.
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
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."
tesk-e zamân, ~ vaqt
Fr.: attribution de temps de télescope
The assignment of telescope time by an expert panel to proposals after evaluating the merits of the observation projects.
Fr.: 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 delay distance
apest-e derang-e zamâni
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: DΔt = (1 + zL)[DA(EL)DA(ES) / DA(LS)], where zL is the → redshift of the → gravitational lens, while DA(EL), DA(ES), and DA(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, DΔt is proportional to 1/H0.