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Pluto Pluton (#) Fr.: Pluton A → dwarf planet in the → solar system which until 2006 was known as the 9th major planet. Pluto revolves around the → Sun in a highly elliptical orbit at a mean distance of 39.5 → astronomical units once every about 248 years. The orbit → eccentricity is 0.25 (compare with the Earth's 0.02) yielding a → perihelion distance of 29.66 → astronomical units and an → aphelion distance of 48.87 AU. Its → orbital inclination is 17 degrees, which is much higher than those of the other planets. Pluto's mass is 1.308 × 10^{22} kg, that is 0.00218 Earth mass (0.177 Moon mass), its equatorial radius ib 0.19 Earth radius, and its → rotation period is equal to 6.39 Earth days. It has five known → satellites, in order of distance from Pluto: → Charon, → Styx, → Nix, → Kerberos, and → Hydra. Pluto's radius is estimated to be about 1150 km (0.18 Earths). Pluto is smaller than seven of the solar system's satellites (the → Moon, → Io (Jupiter I) , → Europa, → Ganymede, → Callisto, → Titan, and → Triton). Pluto's surface has an estimated temperature of 37.5 K and is composed of more than 98% → nitrogen → ice, with traces of → methane and → carbon monoxide. In Roman mythology, Pluto is the god of the underworld and Judge of the dead, from L. Pluto, Pluton, from Gk. Plouton "god of wealth," literally "wealth, riches." Pluto was the son of Saturn. The alternative Gk. name is Hades. |
plutonium plutoniom (#) Fr.: plutonium A → radioactive → chemical element, symbol Pu. → Atomic number 94; → mass number of most stable isotope 244; → melting point 640 °C; → boiling point 3,235 °C. It was first synthesized in 1940 by American chemists Glenn T. Seaborg, Edwin M. McMillan, Joseph W. Kennedy and Arthur C. Wahl in the → nuclear reaction: _{92}U^{238} + _{0}n^{1}→ _{93}Np^{239} + β^{-} (23.5 minutes) → _{94}Pu^{239} + β^{-} (2.36 days). The → half-life of _{94}Pu^{239} is 2.44 × 10^{4} yr. Plutonium-239 is a → fissile isotope. The name derives from the planet → Pluto. It was selected because it is the next planet in the solar system beyond the planet → Neptune and the element plutonium is the next element in the → periodic table beyond → neptunium. |
poach beškaridan Fr.: braconner To trespass, especially on another's game preserve, in order to steal animals or to → hunt; to take game or fish illegally (Dictionary.com). M.E., from M.Fr. pocher "to thrust, poke," from O.Fr. pochier "poke out, gouge, prod," related to poke (v.), from a Germanic source (compare M.H.G. puchen "to pound, beat, knock," Ger. pochen, Middle Dutch boken "to beat") related to poke (v.). Beškaridan, from beškar(d), bišgar(d) "hunter, fowler; chase; game; place for hunting," variant of šekâr, → hunt. |
poacher beškarandé Fr.: braconnier A person who trespasses on private property, especially to catch fish or game illegally (Dictionary.com). See also → hunter. |
poaching beškar Fr.: braconnage The illegal taking of wildlife, in violation of local, state, federal or international law. |
Pogson's ratio vâbar-e Pogson Fr.: rapport de Pogson The constant 2.512, which is the 5th → root of 100 (2.512^{5} = 100); the ratio between two successive stellar → magnitudes. → Pogson's relation; → ratio. |
Pogson's relation bâzâneš-e Pogson Fr.: relation de Pogson The equation that expresses the → magnitude
→ difference between
two objects in terms of the → logarithm of the
→ flux → ratio: Named after Norman Robert Pogson (1829-1891), the English astronomer, who introduced the magnitude scale in 1856; → relation. |
Poincaré recurrence theorem farbin-e bâzâmad-e Poincaré Fr.: théorème de récurrence de Poincaré In an → isolated system, any initial state will occur again in the course of the → evolution of the system over a sufficiently long but finite → time. → Poincaré sphere; → recurrence; → theorem. |
Poincaré sphere kore-ye Poincaré Fr.: sphère de Poincaré A representation that permits an easy visualisation of all different states of → polarization of a vector wave. The equator represents → linear polarization; the north pole corresponds to right-circular and the south pole to left- → circular polarization. Named after Henri Poincaré (1854-1912), French mathematician and theoretical physicist, and a philosopher of science; → sphere. |
Poinsot's motion jonbeš-e Poinsot Fr.: mouvement à la Poinsot The motion of a torque free rotating rigid body in space, in general whose angular velocity vector precesses regularly about the constant angular momentum factor. After Louis Poinsot (1777-1859), French physicist and mathematician. He was the inventor of geometrical mechanics, showing how a system of forces acting on a rigid body could be resolved into a single force and a couple. |
point 1) noqté (#), pandé (#); 2) âmâjidan Fr.: 1) point; 2) pointer 1a) General: A sharp or tapering end, as of a dagger; a projecting part of anything. M.E. point(e); O.Fr. point "dot, mark, place, moment;" L. punctum noun use of neuter p.p. of pungere "to prick, pierce." 1) Noqté, loan from Ar. Pandé, variants in classical dictionaries
pindé, pendé, fand "a point, dot, mole, freckle;" cf. Skt.
prānta- "point, tip, border," from pra "before, forward,"
→ pro-, + ánta- "end, limit, term;"
Pali, panta- "remote, solitary;" Prakrit panta " last;"
Sindhi pandu "border of a garment;" Lahnda pand, pad "end, top of
sugar cane." |
point mass noqté jerm, pandé jerm, jerm-e noqtevâr, ~ pandevâr Fr.: masse ponctuelle A hypothetical object which can be thought of as infinitely small. |
point source noqté xan, pandé xan, xan-e noqtevâr, pande-ye ~ Fr.: source ponctuelle A source of radiation at a great distance from the observer; an ideal source of infinitesimal size. |
point spread function (PSF) karyâ-ye gostareš-e noqté, ~ ~ pandé Fr.: fonction d'étalement du point The two-dimensional intensity distribution about the image of a point source. |
Pointers dorahnemâ Fr.: The two stars that form the front of the Big Dipper's bowl, away from the handle. More specifically, the stars Dubhe (α Ursae Majoris) and Merak (β Ursae Majoris). A line through β to α passes close to the North Star and they are used for finding it. → point + -er. Dorahnemâ, literally "the two guides," from do "two" + rah, râh "way, path" (from Mid.Pers. râh, râs "way, street," also rah, ras "chariot;" from Proto-Iranian *rāθa-; cf. Av. raθa- "chariot;" Skt. rátha- "car, chariot," rathyā- "road;" L. rota "wheel," rotare "to revolve, roll;" Lith. ratas "wheel;" O.H.G. rad; Ger. Rad; Du. rad; O.Ir. roth; PIE *roto- "to run, to turn, to roll") + nemâ agent noun of nemudan "to show" (Mid.Pers. nimūdan, nimây- "to show," from O.Pers./Av. ni- "down; into" (Skt. ni "down," nitaram "downward," Gk. neiothen "from below," cf. E. nether, O.E. niþera, neoþera "down, downward, below, beneath," from P.Gmc. *nitheraz, Du. neder, Ger. nieder; PIE *ni- "down, below") + māy- "to measure;" cf. Skt. mati "measures," matra- "measure;" Gk. metron "measure;" L. metrum; PIE base *me- "to measure"). |
pointing âmâješ Fr.: pointage The act or process of directing a telescope. → point. Verbal noun of → point. |
pointing model model-e âmâješ Fr.: modèle de pointage A mathematical model that reproduces the diurnal rotation of the Earth and is used to direct a telescope toward a precise position on the sky. |
poise poise Fr.: poise The unit of viscosity in the c.g.s. system, equal to 1 dyne.s/cm^{2}. Symbol: P Poise, from Jean-Louis-Marie Poiseuille (1797-1869), a French physiologist and physician who studied the flow of liquids through tubes and developed a method for measuring blood pressure. |
Poiseuille's law qânun-e Poiseuille Fr.: loi de Poiseuille In fluid dynamics, the law that the rate of flow of a liquid through a horizontal tube of uniform radius is directly proportional to the pressure of the liquid and the fourth power of the radius of the tube and is inversely proportional to the viscosity of the liquid and the length of the tube. Named after Jean-Louis-Marie Poiseuille (1797-1869), a French physiologist and physician who found the law in 1844; → law. |
Poisson distribution vâbâžeš-e Poisson Fr.: distribution de Poisson A → probability function that characterizes → discrete → random events occurring independently of one another within some definite time or space. It may be regarded as an approximation of the → binomial distribution when the number of events becomes large and the probability of success becomes small. The Poisson distribution is expressed by: f(x) = (λ^{x}e^{-λ})/x!, where λ is the mean number of successes in the interval, e is the base of the → natural logarithm, and x is the number of successes we are interested in. Named after Siméon Denis Poisson (1781-1840), French mathematician, who developed the application of Fourier series to physical problems and made major contributions to the theory of probability and to the calculus of variations; → distribution. |
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