tarâzmandi-ye gerâneši (#)
Fr.: équilibre gravitationnel
The condition in a celestial body when gravitational forces acting on each point are balanced by some outward pressure, such as radiation pressure or electron degeneracy pressure, so that no vertical motion results.
meydân-e gerâneši (#)
Fr.: champ gravitationnel
The region of space in which → gravitational attraction exists.
niru-ye gerâneši (#)
Fr.: force gravitationnelle
nâpâydâri-ye gerâneši (#)
Fr.: instabilité gravitationnelle
The process by which fluctuations in an infinite medium of size greater than a certain length scale (the Jeans length) grow by self-gravitation.
Fr.: interaction gravitationnelle
Mutual attraction between any two bodies that have mass.
adasi-ye gerâneši (#)
Fr.: lentille gravitationnelle
A concentration of matter, such as a galaxy or a cluster of galaxies, that bends light rays from a background object, resulting in production of multiple images. If the two objects and the Earth are perfectly aligned, the light from the distant object appears as a ring from Earth. This is called an Einstein Ring, since its existence was predicted by Einstein in his theory of general relativity.
Fr.: effet de lentille gravitationelle
The act of producing or the state of a → gravitational lens.
jerm-e gerâneši (#)
Fr.: masse gravitationnelle
The mass of an object measured using the effect of a gravitational field on the object.
gravitational potential energy
kâruž-e tavand-e gerâneši
Fr.: énergie potentielle gravitationnelle
1) The energy that an object possesses because of its position in a
→ gravitational field, especially an object near the
surface of the Earth where the → gravitational acceleration
can be assumed to be constant, at about 9.8 m s-2.
tâbeš-e gerâneši (#)
Fr.: rayonnement gravitationnel
Fr.: décalage vers le rouge gravitationnel
The change in the wavelength or frequency of electromagnetic radiation in a gravitational field predicted by general relativity.
Fr.: décantation par gravité
A physical process occurring in stellar atmospheres whereby in a very stable atmosphere → heavy elements are gravitationally pulled down preferentially. If such an atmosphere is stable for long periods of time, the absorption lines of heavy elements may therefore become very weak. Observationally, the star seems to contain only hydrogen and helium. Gravitational settling takes place in the Sun at the bottom of the outer → convective zone where helium is dragged down, leading to a surface He abundant smaller than the cosmic value. It occurs also in the atmospheres of → brown dwarfs and → planets.
Fr.: fronde gravitationnelle
Same as → gravity assist.
→ gravitational; slingshot, from sling, from M.E. slyngen, from O.N. slyngva "to sling, fling" + shot, from M.E., from O.E. sc(e)ot, (ge)sceot; cf. Ger. Schoss, Geschoss.
Falâxan "sling;" from Av. fradaxšana- "sling," fradaxšanya- "sling, sling-stone;" → gravitational.
mowj-e gerâneši (#)
Fr.: ondes gravitationnelles
A → space-time oscillation created by the motion of matter,
as predicted by Einstein's → general relativity.
When an object accelerates, it creates ripples in space-time, just
like a boat causes ripples in a lake.
Gravitational waves are extremely weak even for the most massive objects like
→ supermassive black holes.
They had been inferred from observing a → binary pulsar
in which the components slow down, due to losing energy from
emitting gravitational waves. Gravitational waves were directly detected for the
first time on September 14, 2015 by the
→ Laser Interferometer Gravitational-Wave Observatory (LIGO).
See also → Laser Interferometer Space Antenna (LISA).
negare-ye meydân-e gerâneši (#)
Fr.: théorie de champ gravitationnel
A theory that treats gravity as a field rather than a force acting at a distance.
Fr.: gravitationnellement lié
A hypothetical force-carrying particle predicted by supersymmetry theories. The gravitino's spin would be 1/2; its mass is unknown.
From gravit(on) + (neutr)ino.
A hypothetical elementary particle associated with the gravitational interactions. This quantum of gravitational radiation is a stable particle, which travels with the speed of light, and has zero rest mass, zero charge, and a spin of ± 2.
From L. gravitatem (nom. gravitas) "weight, heaviness," from gravis "heavy," from PIE base *gwrə- "heavy" (cf. Mod.Pers. gerân "heavy;" Av. gouru- "heavy;" Skt. guru- "heavy, weighty, venerable;" Gk. baros "weight," barys "heavy;" Goth. kaurus "heavy").
Gerâni, noun of gerân "heavy, ponderous, valuable," from Mid.Pers. garân "heavy, hard, difficult;" Av. gouru- "heavy" (in compounds), from Proto-Iranian *garu-; cognate with gravity, as above.
An important astronautical technique whereby a → spacecraft takes up a tiny fraction of the → orbital energy of a planet it is flying by, allowing it to change → trajectory and → speed. Since the planet is not at rest but gravitating around the Sun, the spacecraft uses both the orbital energy and the gravitational pull of the planet. Also known as the slingshot effect or → gravitational slingshot. More specifically, as the spacecraft approaches the planet, it is accelerated by the planet's gravity. If the spacecraft's velocity is too low, or if it is heading too close to the planet, then the planet's → gravitational force will pull it down to the planet. But if its speed is large enough, and its orbit does not bring it too close to the planet, then the gravitational attraction will just bend the spacecraft's trajectory around, and the accelerated spacecraft will pass rapidly by the planet and start to move away. In the absence of other gravitational forces, the planet's gravity would start to slow down the spacecraft as it moves away. If the planet were stationary, the slow-down effect would be equal to the initial acceleration, so there would be no net gain in speed. But the planets are themselves moving through space at high speeds, and this is what gives the "slingshot" effect. Provided the spacecraft is traveling through space in the same direction as the planet, the spacecraft will emerge from the gravity assist maneuver moving faster than before.
→ gravity; assist, from M.Fr. assister "to stand by, help, assist," from L. assistere "assist, stand by," from → ad- "to" + sistere "to cause to stand," from PIE *siste-, from *sta- "to stand" (cognate with Pers. istâdan "to stand").
Yâri "assistance, help; friendship," from yâr "assistant, helper, friend," from Mid.Pers. hayyâr "helper," hayyârêh "help, aid, assistance," Proto-Iranian *adyāva-bara-, cf. Av. aidū- "helpful, useful."