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

1) A general term for anything roughly the size of the → Planck length.
2) Similarly, an energy on the order of the → Planck energy.

→ Planck; → scale.

Same as → blackbody spectrum.

→ Planck; → spectrum.

The time representing the → Planck length divided by the → speed of light. It is expressed by: t_P = (Għ/c⁵)^1/2≅ 5.4 x 10^-44 s, where G is the → gravitational constant, ħ is the → reduced Planck's constant, and c is the → speed of light. At the Planck time, the mass density of the Universe is thought to approach the → Planck density.

→ Planck; → time.

A set of → natural units in which the normalized units are: the gravitational constant, Planck's constant, the speed of light, the Coulomb constant, and Boltzmann's constant.

→ Planck; → unit.

A formula that determines the distribution of intensity of radiation that prevails under conditions of thermal equilibrium at a temperature T: B_v = (2hν³ / c²)[exp(hν / kT) - 1]^-1 where h is Planck's constant and ν is the frequency.

→ Planck; → blackbody; → formula.

→ Planck constant.

→ Planck; → constant.

An equation that expresses the energy radiated per unit area per unit time per unit wavelength range by a blackbody as a function of temperature. It is expressed by → Planck's blackbody formula.

→ Planck; → radiation; → law.

1) (n.) a flat or level surface.
2) (adj.) Of or pertaining to planes or plane figures.

1) From L. plantum "flat surface," noun use of adj. planus "flat, level, plain."
2) From L. planus, as above.

1) Hâmon, variant of hâmun "plain, level ground;" Mid.Pers. hâmôn "level, flat;" Proto-Iranian *hāma-van-, from *hāma- "same, equally, even; together, with" (Mod.Pers./Mid.Pers. ham-; O.Pers./Av. ham-; cf. Skt. sam-; also O.Pers./Av. hama- "one and the same;" Skt. sama-; Gk. homos-; originally identical with PIE numeral *sam- "one," from *som-. The Av. ham- appears in various forms: han- (before gutturals, palatals, dentals) and also hem-, hen-) + *-van- suffix.
2) Taxt "flat;" Mid.Pers. taxtag "tablet, plank, (chess)board."

A two-dimensional geometric figure. The points of the figure lie entirely in a plane.

→ plane; → figure.

A mirror whose reflective surface is neither concave nor convex.

→ plane; → mirror.

In a → linearly polarized light, a plane perpendicular to the → plane of vibration and containing the direction of propagation of light. It is also the plane containing the direction of propagation and the magnetic vector (H) of the electromagnetic light wave.

→ plane; → polarization.

For a rotating object, the plane → perpendicular to the → rotation axis.

→ plane; → rotation.

An imaginary plane that is perpendicular to the → line of sight.

→ plane; → sky.

In a → linearly polarized light, a plane perpendicular to the → plane of polarization and containing the direction of propagation of light. It is also the plane containing the direction of propagation and the electric vector (E) of the electromagnetic light wave.

→ plane; → polarization.

Same as → linear polarization.

→ plane; → polarization.

Light exhibiting → plane polarization. Same as → linearly polarized light.

→ plane; → polarized; → light.

A wave whose wavefronts of constant phase are infinite parallel planes normal to the direction of propagation.

→ plane; → wave.

An approximation used in many stellar atmosphere models that depict the atmosphere as being only one-dimensional and bounded at the top and bottom by horizontal plane surfaces normal to the direction of gravity.

→ plane; → parallel; → atmosphere.

A piece of glass with plane parallel surfaces used to admit light into an optical system and to exclude dirt and moisture.

→ plane; → parallel; → plate.

An object with a mass greater than an → asteroid, but smaller than that of a → brown dwarf.

Short for planetary mass object; → planetary; → mass; → object.