An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A magnetic field whose lines of force are oriented along a particular direction or by a particular manner (axially, vertically; randomly, properly, etc.)

→ aligned; → magnetic field.

The angular diameter of the circle of light that the eye sees through an eyepiece.

→ apparent; → field.

In the → solar dynamo model, a magnetic field that points from east to west or vice-versa.

→ azimuthal; → magnetic; → field.

A → magnetic field whose lines of force (→ line of force) run around the perimeter of the magnet.

→ circular; → magnetic; → field.

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.

→ classical; → field; → theory.

Same as → coercive force.

→ coercive; → field.

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.

→ conservative; → field.

An area on the sky where a large number of objects, commonly stars, are seen gathered together, usually as revealed by imaging.

→ crowded; → field.

An area on the sky whose image is obtained with a deep exposure, such as → Hubble Deep Field.

→ deep; → field.

A → magnetic field produced by a system possessing a net magnetic → dipole moment.

→ dipolar; → magnetic; → field.

A unit used to express the strength of → far ultraviolet (FUV) average → interstellar radiation field. It is equal to ~ 1.7 → Habing field.

Named after B. T. Draine, 1978, ApJS 36, 595.

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: G_μν = -κ T_μν, where G_μν is the → Einstein tensor (a function of the → metric tensor), κ is a coupling constant called the → Einstein gravitational constant, and T_μν 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: G_μν + Λg_μν = - κT_μν, where Λ is the → cosmological constant.

Named after Albert Einstein (1879-1955); → field; → equation.

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.

→ electric; → field.

A region of space consisting of coupled electric and magnetic lines of force at each point, generated by time-varying currents and accelerated charges.

→ electromagnetic; → field.

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.

→ electrostatic; → field.

1) General: An expanse of anything.
2) Physics: A region or space defined by the presence of a physical force, such as electric, magnetic, or gravitational.
3) Math.: A mathematical entity for which addition, subtraction, multiplication, and division are well-defined.

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, arena, extensive plain; town square; gathering place" from Mid.Pers. mêdân "arena, field." Meydân has been borrowed into various languages: Ar. maydân, Turkish meydan, Crimean Tatar, Ukrainian maidan, Polish maidan, also in Pakistan, India, Indonesia, Nepal.

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.

→ field; → curvature.

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.

→ field; → equation.

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; → galaxy.

A → horizontal branch star with high velocity.

→ field; → horizontal; → branch; → star.