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Schroter's effect oskar-e Schröter Fr.: effet de Schröter A phenomenon in which the observed and predicted phases of Venus do not coincide. At eastern elongation, when the planet is visible in the evening sky, dichotomy (half-phase) usually comes a day or two earlier than predicted, while at western elongation dichotomy occurs a day or two later. Named after Johan Schröter (1745-1816), German astronomer, who first described the effect in 1793; → effect. |
Schwarzschild barrier varqe-ye Schwarzschild Fr.: barrière de Schwarzschild An upper theoretical limit to the → eccentricity of orbits near a → supermassive black hole (SBH). It results from the impact of → relativistic precession on the stellar orbits. This phenomenon acts in such a way as to "repel" inspiralling bodies from the eccentric orbits that would otherwise lead to capture as → extreme mass ratio inspiral (EMRI)s. In other words, the presence of the Schwarzschild barrier reduces the frequency of EMRI events, in contrast to that predicted from → resonant relaxation. Resonant relaxation relies on the orbits having commensurate radial and azimuthal frequencies, so they remain in fixed planes over multiple orbits. In the strong-field potential of a massive object, orbits are no longer Keplerian but undergo significant perihelion precession. Resonant relaxation is only efficient in the regime where precession is negligible. The Schwarzschild barrier refers to the boundary between orbits with and without significant precession. Inside this point resonant relaxation is strongly quenched, potentially reducing inspiral rates. |
Schwarzschild black hole siyahcâl-e Schwarzschild Fr.: trou noir de Schwarzschild A → black hole with zero → angular momentum (non-rotating) and zero electric charge derived from Karl Schwarzschild 1916 exact solution to Einstein's vacuum → field equations. Karl Schwarzschild (1873-1916), German mathematical physicist, who carried out the first relativistic study of black holes. → black hole. |
Schwarzschild metric metrik-e Schwarzschild Fr.: métrique de Schwarzschild In → general relativity, the → metric that describes the → space-time outside a static mass with spherically symmetric distribution. |
Schwarzschild radius šo'â'-e Schwarzschild Fr.: rayon de Schwarzschild The critical radius at which a massive body becomes a → black hole, i.e., at which light is unable to escape to infinity: R_{s} = 2GM / c^{2}, where G is the → gravitational constant, M is the mass, and c the → speed of light. The fomula can be approximated to R_{s}≅ 3 x (M/Msun), in km. Therefore, the Schwarzschild radius for Sun is about 3 km and for Earth about 1 cm. |
Schwarzschild singularity takini-ye Schwarzschild Fr.: singularité de Schwarzschild A region of infinite → space-time curvature postulated to lie within a → black hole. |
Schwarzschild solution luyeš-e Schwarzschild Fr.: solution de Schwarzschild The first exact solution of → Einstein's field equations that describes the → space-time geometry outside a spherical distribution of mass. Briefly following Einstein's publication of → General Relativity, Karl Schwarzschild discovered this solution in 1916 (Sitzungsberichte der Königlich Preussischen Akademie der Wissenschaften zu Berlin, Phys.-Math. Klasse, 189); → Schwarzschild black hole. |
Schwarzschild's criterion sanjdiâr-e Schwarzschild Fr.: critère de Schwarzschild The condition in stellar interior under which → convection occurs. It is expressed as: |dT/dr|_{ad} < |dT/dr|_{}rad, where the indices ad and rad stand for adiabatic and radiative respectively. This condition can also be expressed as: ∇_{ad}<∇_{rad}, where ∇ = d lnT / d lnP = P dT / T dP with T and P denoting temperature and pressure respectively. More explicitly, in order for convection to occur the adiabatic temperature gradient should be smaller than the actual temperature gradient of the surrounding gas, which is given by the radiative temperature gradient if convection does not occur. Suppose a hotter → convective cell or gas bubble rises accidentally by a small distance in height. It gets into a layer with a lower gas pressure and therefore expands. Without any heat exchange with the surrounding medium it expands and cools adiabatically. If during this rise and → adiabatic expansion the change in temperature is smaller than in the medium the gas bubble remains hotter than the medium. The expansion of the gas bubble, adjusting to the pressure of the medium, happens very fast, with the speed of sound. It is therefore assumed that the pressure in the gas bubble and in the surroundings is the same and therefore the higher temperature gas bubble will have a lower density than the surrounding gas. The → buoyancy force will therefore accelerate it upward. This always occurs if the adiabatic change of temperature during expansion is smaller than the change of temperature with gas pressure in the surroundings. It is assumed that the mean molecular weight is the same in the rising bubble and the medium. See also → Ledoux's criterion; → mixing length. Named after Karl Schwarzschild (1873-1916), German mathematical physicist (1906 Göttinger Nachrichten No 1, 41); → criterion. |
science dâneš (#) Fr.: science 1) The study of the physical and natural phenomena, especially
by using systematic observation and experiment. M.E., from O.Fr. science, from L. scientia "knowledge," from sciens (genitive scientis), pr.p. of scire "to know," probably originally "to separate one thing from another, to distinguish," related to scindere "to cut, divide;" PIE base *skei- "to cut, split;" cf. Pers. gosastan "to tear, cut, break," from Mid.Pers. wisistan "to break, split," Av. saed-, sid- "to split, break," asista- "unsplit, unharmed;" Skt. chid- "to split, break, cut off;" Gk. skhizein "to split;" Goth. skaidan; O.E. sceadan "to divide, separate." Dâneš, verbal noun of dân-, dânestan "to know" (Mid.Pers. dânistan "to know"), variant šenâxtan, šenâs- "to recognize, to know" (Mid.Pers. šnâxtan, šnâs- "to know, recognize"); O.Pers./Av. xšnā- "to know, learn, come to know, recognize;" cf. Skt. jñā- "to recognize, know," jānāti "he knows;" Gk. gignoskein "to know, think, judge," cognate with L. gnoscere, noscere "to come to know" (Fr. connaître; Sp. conocer); P.Gmc. *knoeanan; O.E. cnawan, E. know; Rus. znat "to know;" PIE base *gno- "to know." |
science fiction dâneš-dizan Fr.: science fiction A form of fiction that draws imaginatively on scientific knowledge and speculation in its plot, setting, theme, etc. (Dictionary.com). |
scientific dâneši, dânešik Fr.: scientifique Of or pertaining to science or the sciences. From M.Fr. scientifique, from M.L. scientificus "pertaining to science," from L. scientia "knowledge," → science, + -ficus "making," from facere "to make." → -ic |
scientific fact bâšâ-ye dâneši, ~ dânešik Fr.: fait scientifique An agreement by competent observers of a series of observations of the same phenomena. From time to time scientific facts are revised by additional data (G. Smooth, Lawrence Berkeley Lab website). → scientific; → fact. |
scientific method raveš-e dâneši Fr.: méthode scientifique The process by which scientists, collectively
and over time, endeavor to construct an accurate (that is, reliable,
consistent, and non-arbitrary) representation of the world.
The scientific method has four steps: → scientific; → method. |
scientific notation namâdgân-e dâneši, ~ dânešik Fr.: notation scientifique A compact format for writing very large or very small numbers. Numbers are made up of three parts: the coefficient, the base and the exponent. For example 3.58 x 10^{4} is the scientific notation for 35,800. → scientific; → notation. |
scientificity dânešigi Fr.: scientificité The quality of the practices and theories that aim at establishing reproducible regularities in phenomena by using experimental method and providing a clearly formulated description. → scientific + → -ity. |
scientist dânešmand (#) Fr.: scientifique An expert in science, especially one of the physical or natural sciences. → scholar. From → science + -ist an agent noun suffix. Dânešmand, from dâneš, → science, + -mand suffix of possession. |
scintillation susu (#) Fr.: scintillation 1) Rapid variation in the brightness, wavelength, and mean position of stars
caused by turbulence in the Earth's atmosphere. From L. scintillationem (nominative scintillatio), from scintillatus p.p. of scintillare "to send out sparks, to flash," from scintilla "particle of fire, spark." Susu, from su "light," related to suz "burning," present stem of suxtan; Mid.Pers. sôxtan, sôzidan "to burn," Av. base saoc- "to burn, inflame" sūcā- "brilliance," upa.suxta- "inflamed;" cf. Skt. śoc- "to light, glow, burn," śocati "burns," śoka- "light, flame;" PIE base *(s)keuk- "to shine." |
scintillation counter susu šomâr Fr.: compteur à scintillation A device for detecting and measuring ionizing radiation by means of flashes produced when the radiation particles strike a sensitive layer of phosphor. → scintillation; → counter. |
scleronomous saxtdâtik Fr.: scléronome Relating to a constraint or system that does not contain time explicitly. For example, a pendulum with an inextensible string of length l_{0} is described by the equation: x^{2} + y^{2} = l_{0}^{2} is both → holonomic and scleronomous. From Gk. sclero-, from skleros "hard" + -nomous, → -nomy. |
Scorpius Každom (#) Fr.: Scorpion The Scorpion. A large and impressive constellation in the → Zodiac, which lies between → Libra to the west and → Sagittarius to the east. Scorpius is located in the southern hemisphere near the center of the Milky Way at approximately 17h right ascension, -40° declination. The bright, red star → Antares marks the heart of the scorpion. The constellation contains deep sky objects such as the open clusters M6 and M7, and the globular clusters M4 and M80. Also in the southern end of the constellation there is the open star cluster NGC 6231. Abbreviation: Sco; genitive: Scorpii. M.E., from O.Fr. scorpion, from L. scorpionem (nominative scorpio), from Gk. skorpios "a scorpion," from PIE base *(s)ker- "to cut," → shear. According to Gk. mythology, the constellation represents a giant scorpion sent forth by the earth-goddess Gaia to kill the giant Orion when he threatened to slay all the beasts of the earth. Orion and the Scorpion were afterward placed amongst the stars as a pair of constellations. The two opponents are never seen in the sky at the same time, for one constellation sets as the other rises. The scorpion's claws were originally formed by Libra. Každom "scorpion," variants kajdom, gaždom literally "crooked tail," from Mid.Pers. gazdum literally "stinging tail," from gaz present stem of gazidan (also Mod.Pers.) "to sting, to bite" + dum, dumb (Mod.Pers. dom, domb) "tail;" Av. duma- "tail." |
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