"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.
Einstein's gravitational constant
pâyâ-ye gerâneši-ye Einstein (#)
Fr.: constante gravitationnelle d'Einstein
Gaussian gravitational constant
pâyâ-ye gerâneši-ye Gauss
Fr.: 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.
Of or relating to or caused by → gravitation.
Adj. of → gravitation.
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.
Fr.: attraction gravitationnelle
The force that pulls material bodies toward one another because of → gravitation.
rombeš-e gerâneši (#)
Fr.: effondrement gravitationnel
Collapse of a mass of material as a result of the mutual → gravitational attraction of all its constituents.
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.
Fr.: contraction gravitationnelle
Decrease in the volume of an astronomical object under the action of a dominant, central gravitational force.
Fr.: rencontre gravitationnelle
An encounter in which two moving bodies alter each other's direction and velocity by mutual → gravitational attraction.
Fr.: énergie gravitationnelle
Same as → gravitational potential energy.
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.
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.
Fr.: effet de lentille gravitationelle
The act of producing or the state of a → gravitational lens.
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.