aligned magnetic field
meydân-e meqnâtisi-ye âxatidé
Fr.: champ magnétique aligné
A magnetic field whose lines of force are oriented along a particular direction or by a particular manner (axially, vertically; randomly, properly, etc.)
Fr.: champ apparent
The angular diameter of the circle of light that the eye sees through an eyepiece.
azimuthal magnetic field
meydân-e meqnâtisi-ye sugâni
Fr.: champ magnétiquue azimutal
In the → solar dynamo model, a magnetic field that points from east to west or vice-versa.
classical field theory
negare-ye klâsik-e meydân
Fr.: théorie classique des champs
The theory that studies distributions of → energy, → matter, and other physical quantities under circumstances where their discrete nature is unimportant. Classical field theory traditionally includes → Newtonian mechanics, Maxwell's → electromagnetic theory, and Einstein's theory of → general relativity. The main scope of classical field theory is to construct the mathematical description of → dynamical systems with an infinite number of degrees of freedom. The word "classical" is used in contrast to those field theories that incorporate → quantum mechanics (→ quantum field theory). Classical field theories are usually categorized as → non-relativistic and → relativistic.
Fr.: champ conservatif
A → field of → force in which the → work done in taking a particle from one point to another is independent of the → path taken between them. Examples are → electrostatic field and → gravitational field.
Fr.: champ encombré
An area on the sky where a large number of objects, commonly stars, are seen gathered together, usually as revealed by imaging.
Fr.: champ profond
An area on the sky whose image is obtained with a deep exposure, such as → Hubble Deep Field.
Fr.: champ de Draine
Named after B. T. Draine, 1978, ApJS 36, 595.
Einstein's field equations
hamugešhâ-ye meydân-e Einstein
Fr.: équations de champ d'Einstein
A system of ten non-linear → partial differential equations in the theory of → general relativity which relate the curvature of → space-time with the distribution of matter-energy. They have the form: Gμν = -κ Tμν, where Gμν is the → Einstein tensor (a function of the → metric tensor), κ is a coupling constant called the → Einstein gravitational constant, and Tμν is the → energy-momentum tensor. The field equations mean that the curvature of space-time is due to the distribution of mass-energy in space. A more general form of the field equations proposed by Einstein is: Gμν + Λgμν = - κTμν, where Λ is the → cosmological constant.
meydân-e barqi (#)
Fr.: champ électrique
The effect produced by the existence of an → electric charge in the volume of space that surrounds it. The direction of the field is taken to be the direction of the force it would exert on a positive test charge. The electric field is radially outward from a positive charge and radially in toward a negative point charge.
Fr.: champ électromagnétique
A region of space consisting of coupled electric and magnetic lines of force at each point, generated by time-varying currents and accelerated charges.
meydân-e barqistâ (#)
Fr.: champ électrostatique
A region of space in which a non-moving → electric charge would be subjected to a force of attraction or repulsion as a result of the presence of another stationary electric charge. The electrostatic field is a special case of the → electromagnetic field.
1) General: An expanse of anything.
M.E., from O.E. feld "plain, open land," probably related to O.E. folde "earth, land," from P.Gmc. *felthuz "flat land" (cf. Ger. Feld), from PIE *pel(e)-tu-,from base *pele- "flat, to sprea;" cf. L. planus "flat, level," → plane.
Meydân "field, field of battle, arena, extensive plain," from Mid.Pers. mêdân "arena, field." This term is loaned into Ar. from Pers. or Mid.Pers.
xamidegi-ye meydân (#)
Fr.: courbure de champ
An aberration in an optical instrument, common in Schmidt telescopes, in which the focus changes from the center to the edge of the field of view. Owing to this aberration, a straight object looks curved in the image.
Fr.: équation de champ
In a physical theory, an equation that describe how a fundamental force interacts with matter. Einstein's equations of → general relativity are called field equations since they describe the → gravitational field. Similarly, → Maxwell's equations describe the electromagnetic field.
Fr.: galaxie de champ
A galaxy that lies in the direction of a → cluster of galaxies, but is not a member of the cluster. Field galaxies are rare, less than about 5% of all galaxies.
field horizontal branch star
setâre-ye šâxe-ye ofoqi-ye meydâni
Fr.: étoile de la branche horizontal du champ
A → horizontal branch star with high velocity.
Fr.: lentille de champ
A lens placed at or near the focal plane of a telescope to create an image of the primary mirror inside the instrument.
field O star
setâre-ye O-ye meydân
Fr.: étoile O de champ
An → O-type star which is apparently not associated with a → star cluster. A significant fraction of → massive stars in the → Milky Way and other galaxies are located far from star clusters and → star-forming regions. It is known that some of these stars are → runaways, i.e. possess high → space velocities (determined through the → proper motion and/or → radial velocity measurements), and therefore most likely were formed in embedded clusters and then ejected into the field because of dynamical interactions or → binary-→ supernova explosions. However, there exists a group of field O stars whose runaway status is difficult to prove via direct proper motion measurements or whose low space velocities and/or young ages appear to be incompatible with their large separation from known star clusters. The existence of this group led some authors to believe that these stars can form → in situ. The question of whether or not O stars can form in isolation (→ isolated massive star formation) is of crucial importance for → star formation models (Gvaramadze et al., 2012, MNRAS, 424, 3037).
Fr.: objet de champ
An astronomical object that is seen in the direction of a group but not physically belonging to the group. → field galaxy.