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grating groove šiyâr-e turi (#) Fr.: trait du réseau, sillon ~ ~ One of thousands of long, narrow indentations in the surface of a → diffraction grating. |
gravitate gerânidan (#) Fr.: graviter To move or tend to move under the influence of gravitational force. From L. gravitatus, p.p. of gravitâre, from gravis "heavy," → gravity. Gerânidan, infinitive of gerân, → gravity. |
gravitation gerâneš (#) Fr.: gravitation 1) The universal phenomenon of attraction between material bodies.
→ Newton's law of gravitation. Verbal noun of → gravitate. |
gravitational gerâneši (#) Fr.: gravitationnel Of or relating to or caused by → gravitation. Adj. of → gravitation. |
gravitational acceleration šetâb-e gerâneši (#) Fr.: accélération gravitationnelle The acceleration caused by the force of gravity. At the Earth's surface it is determined by the distance of the object form the center of the Earth: g = GM/R^{2}, where G is the → gravitational constant, and M and R are the Earth's mass and radius respectively. It is approximately equal to 9.8 m s^{-2}. The value varies slightly with latitude and elevation. Also known as the → acceleration of gravity. → gravitational; → acceleration. |
gravitational attraction darkešeš-e gerâneši Fr.: attraction gravitationnelle The force that pulls material bodies toward one another because of → gravitation. → gravitational; → attraction. |
gravitational collapse rombeš-e gerâneši (#) Fr.: effondrement gravitationnel Collapse of a mass of material as a result of the mutual → gravitational attraction of all its constituents. → gravitational; → collapse. |
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 lens equation hamugeš-e adasi-ye gerâneši Fr.: équation de lentille gravitationnelle The main equation of gravitational lens theory that sets a relation between the angular position of the point source and the observable position of its image. → gravitational; → lens; → equation. |
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 with the observer, and obey some conditions on their distances (→ Einstein radius), 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 time 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. |
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