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gravitational constant pâyâ-ye gerâneši (#) Fr.: constante gravitationnelle A fundamental constant that appears in → Newton's law of gravitation. It is the force of attraction between two bodies of unit mass separated by unit distance: G = 6.673 x 10^{-8} dyn cm^{2} g^{-2} or 6.673 x 10^{-8} cm^{3}s^{-2}g^{-1}, or 6.673 x 10^{-11} N m^{2} kg^{-2} or 6.673 x 10^{-11} m^{3}s^{-2}kg^{-1}. It was first measured in 1798 by Henry Cavendish (1731-1810), 71 years after Newton's death. Same as the → Newtonian constant of gravitation. → gravitational; → constant. |
gravitational contraction terengeš-e gerâneši Fr.: contraction gravitationnelle Decrease in the volume of an astronomical object under the action of a dominant, central gravitational force. → gravitational; → contraction. |
gravitational encounter ruyâruyi-ye gerâneši Fr.: rencontre gravitationnelle An encounter in which two moving bodies alter each other's direction and velocity by mutual → gravitational attraction. → gravitational; → encounter. |
gravitational energy kâruž-e gerâneši Fr.: énergie gravitationnelle Same as → gravitational potential energy. → gravitational; → energy. |
gravitational equilibrium 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. → gravitational; → equilibrium. |
gravitational field meydân-e gerâneši (#) Fr.: champ gravitationnel The region of space in which → gravitational attraction exists. → gravitational; → field. |
gravitational force niru-ye gerâneši (#) Fr.: force gravitationnelle The weakest of the four fundamental forces of nature. Described by → Newton's law of gravitation and subsequently by Einstein's → general relativity. → gravitational; → force. |
gravitational instability 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. → gravitational; → instability. |
gravitational interaction andaržireš-e gerâneši Fr.: interaction gravitationnelle Mutual attraction between any two bodies that have mass. → gravitational; → interaction. |
gravitational lens 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. → gravitational; → lens. |
gravitational lensing lenzeš-e gerâneši Fr.: effet de lentille gravitationelle The act of producing or the state of a → gravitational lens. → gravitational; → lensing. |
gravitational lensing time delay derang-e zâyide-ye lenzeš-e gerâneši Fr.: retard dû à l'effet de lentille gravitationnelle The difference in light travel times along the various light paths from the source to the observer when the source image is divided into several images because of → gravitational lensing. According to the theory of → general relativity, light rays are deflected in the vicinity of massive objects. If the light source, and the deflector are sufficiently well aligned, we can observe several (generally distorted and magnified) images of the source. A property of → strong lensing is that the light travel time from the source to the observer is generally not identical for the different images. In other words, we not only see several images of one same object, but we also see this object, in each image, at different times. This means, in one image the lensed object will be observed before the other image. Given a physical model of the gravitational lens, the light travel time for each image can be computed. The expression giving the time delay has two components: a term is called → geometric delay, and the second term, known as the → Shapiro delay. The latter is due to time dilation by the gravitational field of the lens, a direct consequence of general relativity. See also → time delay distance. → gravitational; → lensing; → time; → delay. |
gravitational mass jerm-e gerâneši (#) Fr.: masse gravitationnelle The mass of an object measured using the effect of a gravitational field on the object. → gravitational; → mass. |
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}. → gravitational; → potential; → energy. |
gravitational radiation tâbeš-e gerâneši (#) Fr.: rayonnement gravitationnel The → energy transported by → gravitational waves. Gravitational radiation is to → gravity what light is to → electromagnetism. → gravitational; → radiation. |
gravitational redshift sorxkib-e gerâneši Fr.: décalage vers le rouge gravitationnel The change in the wavelength or frequency of electromagnetic radiation in a gravitational field predicted by general relativity. → gravitational; → redshift. |
gravitational settling niyâšeš-e gerâneši 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. → gravitational; → settling. |
gravitational slingshot falâxan-e gerâneši 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. |
gravitational wave 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). → gravitational; → wave. |
gravitational-field theory 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. → gravitational; → field. |
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