plane polarized light
nur-e qotbide-ye hâmoni
Fr.: lumière polarisée plane
mowj-e taxt (#)
Fr.: onde plane
A wave whose wavefronts of constant phase are infinite parallel planes normal to the direction of propagation.
havâsepehr-e parâsu-taxthâ, javv-e ~
Fr.: atmosphère plan-parallèle
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.
Fr.: lame plan-parallèle
A piece of glass with plane parallel surfaces used to admit light into an optical system and to exclude dirt and moisture.
1) A celestial body that: (a) is in orbit around the Sun, (b) has
sufficient mass for its self-gravity 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."
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 → trans-Neptunian 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 super-Earth 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 (400-1500 AU) and eccentricities (0.5-0.8) 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.
1) âsmânnemâ; 2) âsmânxâné (#)
1) A device that produces a representation of the heavens by the use of a number of
From → planet + -arium "a place for."
&ACIRC;smânnemâ, literally "sky displayer," from
âsmân "sky" (Mid.Pers. âsmân "sky, heaven;"
"heaven;" Av. asman- "stone, sling-stone; heaven;" cf. Skt. áśman-
"stone, rock, thunderbolt;" Gk. akmon "heaven, meteor, anvil;" Akmon
was the father of Ouranos (Uranus), god of sky; Lith. akmuo "stone;" Rus. kamen;
PIE base *akmon- "stone, sky."
The link between the "stone" and "sky" concepts indicates that the sky had once been conceived
as a stone vault by prehistoric Indo-Europeans) +
nemâ "displayer," from
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
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").
Of, pertaining to, or resembling a planet or planets.
Fr.: aberration planétaire
The difference between the true position of a planet and its apparent position, due to the time required for light to travel the distance from the planet to Earth. Correction for planetary aberration is necessary in determining orbits.
Fr.: nébuleuse planétaire
A hot envelope of gas ejected from a central evolved star before becoming a → white dwarf. At the end of the → asymptotic giant phase the pulsating → red giant star is surrounded by an extended shell formed by the material ejected from it. As the evolved star contracts, its → effective temperature rises considerably. When it reaches about 30,000 K, the radiated photons become energetic enough to ionize the atoms in the nebula. The nebula becomes then visible in the optical. It shines essentially in a few → emission lines, produced by cascades during recombination or by collisional excitation with electrons. The central stars of planetary nebulae, → CSPNe, are typically 0.6 to 0.8 solar masses. They have → main sequence masses in the range 1 to 8 solar masses, with an average mass of 2.2 solar masses for a standard → initial mass function. Thus a total of about 1.6 solar masses is in average lost during the → AGB and planetary nebula phases. The life-time of planetary nebulae is relatively short. A typical planetary nebula lasts only a few 10,000 years.
→ planetary; → nebula. The name comes from the fact that these objects appear as planetary disks in a low-resolution telescope. The first planetary nebula, designated NGC 7009 or the → Saturn Nebula, was discovered in 1782 by the German-born English astronomer William Herschel (1738-1822), who described it as "planetary nebula."
fizik-e sayyâregân (#)
Fr.: physique des planètes
The study of the structure, composition, as well as physical and chemical properties of the planets of the solar system, including their atmospheres and their immediate cosmic environment.
Fr.: précession planétaire
The motion of the → ecliptic plane caused by the gravitational influence of the other planets, mainly → Jupiter. The observational effect of planetary precession is similar to that of the → lunisolar precession. But planetary precession causes the → equinoxes to move along the ecliptic in the opposition direction (eastward) from that of luni-solar precession (westward) and at a much slower rate: 0''.12 per year. Same as → precession of ecliptic.
planetary ring system
râžmân-e halqehâ-ye sayyâre-yi
Fr.: système d'anneaux planétaires
→ Interplanetary dust and other small particles organized into thin, flat rings encircling a planet. The most spectacular planetary rings known are those around → Saturn, but the other three → giant planets of the solar system (→ Jupiter, → Uranus, and → Neptune) have their own ring systems.
The branch of astronomy that deals with the science of planets, or planetary systems, and the solar system.
Fr.: système planétaire
A system composed of a star and all the celestial bodies bound to it by gravity, especially planets and their natural satellites.
gozar-e sayyâre-yi (#)
Fr.: transit planétaire
The passage of an → inferior planet against the disk of the Sun, as viewed from Earth. Mercury and Venus pass in front of the Sun only when they are close to one of their → orbital nodes, at → inferior conjunction. For Mercury this occurs at the beginning of November (the → ascending node) or at the beginning of May (the → descending node), while for Venus it takes place at the beginning of December (the ascending node) or at the beginning of June (the descending node). See also → transit of Mercury, → transit of Venus.
PLAnetary Transits and Oscillations of stars (PLATO)
A space observatory under development by the → European Space Agency for launch around 2024. Its objective is to detect and characterize → exoplanets by means of their → transit signature in front of a very large sample of → bright stars, and measure the seismic oscillations (→ asteroseismology) of the parent stars orbited by these planets in order to understand the properties of the exoplanetary systems.
Any of numerous small solid bodies in a → protoplanetary disk that in some cases clump together to form → planets but in other cases remain relatively small and become → asteroids and → comets. Similarly, → Kuiper Belt Objects are probably the remnants of the planetesimals that formed the planets.
Xordesayyâré, from xordé "small, minute; crumbs," from xord "minute, little, small" (from Mid.Pers. xvart, xôrt "small, insignificant;" Av. ādra- "weak, dependent;" Skt. ādhrá- "small, weak, poor," nādh "to be oppressed;" Gk. nothros "sluggish;" PIE base *nhdhro-) + sayyâré, → planet.
An older equivalent for → asteroid.