# An Etymological Dictionary of Astronomy and AstrophysicsEnglish-French-Persian

## فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

### M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 35 Search : gravitational
 "nongravitational forces"   "نیروهای ِ ناگرانشی"   "niruhâ-ye nâgerâneši" (#)Fr.: "forces non-gravitationnelles"   The forces of jets from a comet's nucleus that can cause a rocket-like effect and alter a comet's direction of motion slightly.→ non-; → gravitational; → force. Einstein's gravitational constant   پایای ِ گرانشی ِ اینشتین   pâyâ-ye gerâneši-ye Einstein (#)Fr.: constante gravitationnelle d'Einstein   The coupling constant appearing in → Einstein's field equations, expressed by: κ = 8πG/c4, where G is the Newtonian → gravitational constant and c the → speed of light.→ einstein; → gravitational; → constant. Gaussian gravitational constant   پایای ِ گرانشی ِ گاؤس   pâyâ-ye gerâneši-ye GaussFr.: constante gravitationnelle de Gauss   The constant, denoted k, defining the astronomical system of units of length (→ astronomical unit), mass (→ solar mass), and time (→ day), by means of → Kepler's third law. The dimensions of k2 are those of Newton's constant of gravitation: L 3M -1T -2. Its value is: k = 0.01720209895.→ Gaussian; → gravitational; → constant. gravitational   گرانشی   gerâneši (#)Fr.: gravitationnel   Of or relating to or caused by → gravitation.Adj. of → gravitation. gravitational acceleration   شتاب ِ گرانشی   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/R2, 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 attraction   درکشش ِ گرانشی   darkešeš-e gerânešiFr.: attraction gravitationnelle   The force that pulls material bodies toward one another because of → gravitation. gravitational collapse   رمبش ِ گرانشی   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 constant   پایای ِ گرانشی   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 cm2 g-2 or 6.673 x 10-8 cm3s-2g-1, or 6.673 x 10-11 N m2 kg-2 or 6.673 x 10-11 m3s-2kg-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 contraction   ترنگش ِ گرانشی   terengeš-e gerânešiFr.: contraction gravitationnelle   Decrease in the volume of an astronomical object under the action of a dominant, central gravitational force. gravitational encounter   رویارویی ِ گرانشی   ruyâruyi-ye gerânešiFr.: rencontre gravitationnelle   An encounter in which two moving bodies alter each other's direction and velocity by mutual → gravitational attraction. gravitational energy   کاروژ ِ گرانشی   kâruž-e gerânešiFr.: énergie gravitationnelle   Same as → gravitational potential energy.→ gravitational; → energy. gravitational equilibrium   ترازمندی ِ گرانشی   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 field   میدان ِ گرانشی   meydân-e gerâneši (#)Fr.: champ gravitationnel   The region of space in which → gravitational attraction exists.→ gravitational; → field. gravitational force   نیروی ِ گرانشی   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   ناپایداری ِ گرانشی   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 interaction   اندرژیرش ِ گرانشی   andaržireš-e gerânešiFr.: interaction gravitationnelle   Mutual attraction between any two bodies that have mass. gravitational lens   عدسی ِ گرانشی   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   هموگش ِ عدسی ِ گرانشی   hamugeš-e adasi-ye gerânešiFr.: 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   لنزش ِ گرانشی   lenzeš-e gerânešiFr.: effet de lentille gravitationelle   The act of producing or the state of a → gravitational lens.→ gravitational; → lensing. gravitational lensing time delay   درنگ ِ زاییده‌ی ِ لنزش ِ گرانشی   derang-e zâyide-ye lenzeš-e gerânešiFr.: 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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