<< < "no abe acc act aff ama ani ant aps ast atm aut bar bic Boh bou cal car cel che cla col com com Com con con con con con con con con con con con con Cor cor cot cul de- dec dem des dif dil dir dis dom dyn Edd ele ele emi equ Eve exc exp fac fin for fre fuz gen Glo gra gra Ham hel hor hyd ign inc inf Inf int Int int ion irr jum Lag lea lig lin Lor Lyo mag mat met min Mon moo NaC neg New New non non non nul obs one opt Ori oxi par per per phl pho pla Pla pol pos pre pro pro pse qua rad rad rea rec reg rel res ret rot Ryd sci sec sec seq sim Sod sor spe sta ste sto sub sup syn the Tho Tor tra tru und vec vio wav Wil zir > >>
Platonic year sâl-e Plâtoni, ~ Aflâtuni Fr.: année platonique The time required for a complete revolution of the Earth's pole on the celestial sphere as the result of → precession. A Platonic year is equal to 25 800 years. Of or pertaining to Gk. philosopher Plato, from Gk. Platon "broad-shouldered," from platys "broad." → year. |
Pleione Pleyoné (#) Fr.: Pléioné A star in the constellation → Taurus and a member of the → Pleiades star cluster. Pleione is a blue-white B-type → main sequence → dwarf with a mean apparent magnitude of +5.09. It is a variable star and its brightness varies from magnitude +4.77 to +5.50. It is approximately 380 light-years from Earth. Pleione was an Oceanid nymph. She lived in a southern region of Greece called Arcadia, on a mountain named Mount Kyllini. She married Atlas and gave birth to the Hyades, Hyas and the Pleiades. |
plerion plerion Fr.: plérion A → supernova remnant which has a filled center rather than being a shell. The internal region is "filled" by energetic particles streaming from a rotating → pulsar. The → Crab Nebula is the archetypal plerion. Plerion, from Gk. pleres "full," akin to Pers. por "full," → poly-. |
plutonium plutoniom (#) Fr.: plutonium A → radioactive → chemical element, symbol Pu. → Atomic number 94; → mass number of most stable isotope 244; → melting point 640 Â°C; → boiling point 3,235 Â°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. |
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. |
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 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. |
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. |
Poisson's equation hamugeš-e Poisson Fr.: équation de Poisson An equation (∇^{2}φ = 4πGρ) which relates the gravitational (or electromagnetic) potential to the mass density (or charge density). → Poisson distribution; → equation. |
polar bond band-e qotbi Fr.: lien polaire A chemical bond where the electrons are shared unequally between atoms. The atom that is more electronegative will pull the electrons closer to itself. |
polar equation hamugeš-e qotbi Fr.: équation polaire An equation for a curve written in terms of the → polar coordinates. |
polar motion jonbeš-e qotbi Fr.: mouvement du pÃ´le The irregularly varying motion of the Earth's pole of rotation with respect to the Earth's crust. |
polarization qotbeš (#) Fr.: polarisation 1) Optics: A process or state in which the directions of the electric or magnetic fields
of an → electromagnetic radiation
change in a regular pattern. Light can be polarized by a
variety of ways, involving the following processes: reflection, transmission,
double refraction, and scattering. See also
→ unpolarized light;
→ linear polarization;
→ circular polarization;
→ elliptical polarization.
The study of the polarization of light from astronomical sources can yield
unique information in particular related to the properties of magnetic fields. Verbal noun of → polarize. |
polarization angle zâviye-ye qotbeš (#) Fr.: angle de polarisation Same as → polarizing angle and → Brewster angle. → polarization; → angle. |
polarization charge bâr-e qotbeš Fr.: Same as → bound charge. → polarization; → charge. |
polarization degree daraje-ye qotbeš (#) Fr.: degrÃ© de polarisation → polarization; → degree. |
polarization fraction barxe-ye qotbeš Fr.: fraction de polarisation The ratio expressed by P = (I_{par} - I_{per}) / (I_{par} + I_{per}), where I_{par} and I_{per} are the light intensities with the electric field vector respectively parallel and perpendicular to the incident beam. → polarization; → fraction. |
pollution âludegi (#) Fr.: pollution The introduction of harmful substances or light into the natural environment
as a consequence of human activities. → light pollution. M.E., from O.Fr., from L.L. pollutionem "defilement," from L. polluere "to soil, defile," from pol-, variant of por- "forth, forward, before" + -luere "smear," related to lutum "mud," and to lues "filth; plague, pestilence;;" cf. Gk. luma "filth, dirt, disgrace;" O.Ir. loth "mud, dirt;" Lith. lutynas "pool, puddle;" Pers. âludan, as below. &ACIRC;ludegi, from âludan, âlây-"to pollute, soil, stain;" Mid.Pers. âlutan; from prefixed Proto-Iranian *ā-rūta-, from rav- "to stain, soil;" Mid.Pers. Manichean Parthian rwd "rascal;" PIE base *leu- "dirty; to soil;" cf. L. lues, as above. |
polonium poloniom (#) Fr.: polonium A radioactive chemical element; symbol Po. Atomic number 84; mass number of most stable isotope 209; melting point 254Â°C; boiling point 962Â°C. The name derives from Poland, the native country of Marie Sklodowska Curie. It was discovered by Pierre and Marie Curie in 1898, from its radioactivity. |
<< < "no abe acc act aff ama ani ant aps ast atm aut bar bic Boh bou cal car cel che cla col com com Com con con con con con con con con con con con con Cor cor cot cul de- dec dem des dif dil dir dis dom dyn Edd ele ele emi equ Eve exc exp fac fin for fre fuz gen Glo gra gra Ham hel hor hyd ign inc inf Inf int Int int ion irr jum Lag lea lig lin Lor Lyo mag mat met min Mon moo NaC neg New New non non non nul obs one opt Ori oxi par per per phl pho pla Pla pol pos pre pro pro pse qua rad rad rea rec reg rel res ret rot Ryd sci sec sec seq sim Sod sor spe sta ste sto sub sup syn the Tho Tor tra tru und vec vio wav Wil zir > >>