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Planck time zamâne Planck Fr.: temps de Planck The time representing the → Planck length divided by the → speed of light. It is expressed by: t_{P} = (Għ/c^{5})^{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 units yekâhâye Planck (#) Fr.: unités de Planck 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's blackbody formula disule siyah jesme Planck Fr.: formule du corps noir de Planck A formula that determines the distribution of intensity of radiation that prevails under conditions of thermal equilibrium at a temperature T: B_{v} = (2hν^{3} / c^{2})[exp(hν / kT)  1]^{1} where h is Planck's constant and ν is the frequency. 
Planck's constant pâyâye Planck (#) Fr.: constante de Planck 
Planck's radiation law qânune tâbeše Planck Fr.: loi du rayonnement de Planck 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. 
plane 1) hâmon (#); 2) taxt (#) Fr.: plan 1) (n.) a flat or level surface. 1) From L. plantum "flat surface," noun use of adj. planus "flat,
level, plain." 1) Hâmon, variant of hâmun "plain, level ground;" Mid.Pers. hâmôn
"level, flat;" ProtoIranian *hāmavan,
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.

plane figure šekle hâmon, ~ taxt Fr.: figure plane A twodimensional geometric figure. The points of the figure lie entirely in a plane. 
plane mirror âyeneye taxt (#) Fr.: miroir plan A mirror whose reflective surface is neither concave nor convex. 
plane of polarization hâmone qotbeš Fr.: plan de polarisation 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. 
plane of rotation hâmone carxeš Fr.: plan de rotation For a rotating object, the plane → perpendicular to the → rotation axis. 
plane of the sky hâmone âsmân Fr.: plan du ciel An imaginary plane that is perpendicular to the → line of sight. 
plane of vibration hâmone šiveš Fr.: plan de vibration 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. 
plane polarization qotbeše hâmoni Fr.: polarisation plane Same as → linear polarization. → plane; → polarization. 
plane polarized light nure qotbideye hâmoni Fr.: lumière polarisée plane Light exhibiting → plane polarization. Same as → linearly polarized light. 
plane wave mowje taxt (#) Fr.: onde plane A wave whose wavefronts of constant phase are infinite parallel planes normal to the direction of propagation. 
planeparallel atmosphere havâsepehre parâsutaxthâ, javve ~ Fr.: atmosphère planparallèle An approximation used in many stellar atmosphere models that depict the atmosphere as being only onedimensional and bounded at the top and bottom by horizontal plane surfaces normal to the direction of gravity. → plane; → parallel; → atmosphere. 
planeparallel plate tiqeye taxtparâsu Fr.: lame planparallèle A piece of glass with plane parallel surfaces used to admit light into an optical system and to exclude dirt and moisture. 
planemo planemo Fr.: planemo 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. 
planet sayyâré (#) Fr.: planète 1) A celestial body that: (a) is in orbit around the Sun, (b) has
sufficient mass for its selfgravity to overcome rigid body forces so
that it assumes a hydrostatic equilibrium (nearly round) shape, and
(c) has cleared the neighborhood around its orbit.
→ dwarf planet.
From O.E., from O.Fr. planete (Fr. planète), from L.L. planeta (plural form planetae), from Gk. planetes (single form) "wandering," from (asteres) planetai "wandering (stars)," from planasthai "to wander," of unknown origin. Sayyâré, from Ar. saiyârat "walker, traveller." 
Planet Nine sayyâreye noh Fr.: Planète Neuf A hypothetical large planet in the far outer → solar system the gravitational effects of which would explain the unexpected orbital configuration of a group of → transNeptunian objects (TNOs). Trujillo & Sheppard (2014) noticed a clustering of the → argument of perihelion of bodies lying beyond ~150 → astronomical unit (AU), and attributed this to a hypothetical superEarth body lying at several hundred AUs. Batygin & Brown (2016) showed numerically and analytically how the apsidal and nodal clustering of the distant TNOs arises as a result of resonant and secular dynamical effects from a distant perturber. They identified a range of semimajor axes (4001500 AU) and eccentricities (0.50.8) for which a distant planet can explain the → orbital elements of the distant TNOs. The predicted planet would have a mass of 10 Earths (approximately 5,000 times the mass of → Pluto), a diameter of four times Earth and a highly elliptical orbit with an → orbital period of approximately 15,000 years. 
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