An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



<< < -sc Sag sam sat sca sca Sch sci Sea sec sec see sel sem sen ser Sey Sha she sho sid sig SIM sim Sin ske sle Smi SNR sof sol sol sol sol sou sou spa spa spe spe spe sph spi spi Spo squ sta sta sta sta Ste ste ste sto str str str sub sub sub sun sup sup sup sup sur sus sym syn syz > >>

Number of Results: 1381
Schröter's effect
  اُسکر ِ شروتر   
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.

Schrodinger equation
  هموگش ِ شرودینگر   
hamugeš-e Schrödinger

Fr.: équation de Schrödinger   

A fundamental equation of physics in → quantum mechanics the solution of which gives the → wave function, that is a mathematical expression that contains all the information known about a particle. This → partial differential equation describes also how the wave function of a physical system evolves over time.

Named after Erwin Schrödinger (1887-1961), the Austrian theoretical physicist, Nobel Prize 1933, who first developed the version of quantum mechanics known as → wave mechanics; → equation.

Schrodinger's cat
  گربه‌ی ِ شرودینگر   
gorbe-ye Schrödinger (#)

Fr.: chat de Schrödinger   

A → thought experiment intended to illustrate the → superposition principle in → quantum mechanics. A cat is put in a steel box which is separated from the outside world. The box also contains a vial of lethal acid, a tiny amount of a radioactive substance, a → Geiger counter, and a hammer. If an atom decays and the Geiger counter detects an → alpha particle, the hammer breaks the vial which kills the cat. According to Schrödinger, as long as the box stays closed the cat's fate is tied to the → wave function of the atom, which is itself in a superposition of decayed and un-decayed states. Thus the cat must itself be in a superposition of dead and alive states before the observer opens the box, "observes" the cat, and "collapses" its wave function. However, Schrödinger's argument fails because it rests on the assumption that macroscopic objects can remain unobserved in a superposition state. When an atom decays, its wave function becomes entangled with the enormously complex wave function of the macroscopic Geiger counter. The atom is therefore "observed" by the Geiger counter. Since a Geiger counter cannot, for all practical purposes, be isolated from the rest of the world, the rest of the world observes the atom, and the cat is either dead or alive. → collapse of the wave function.

Named after Erwin Schrödinger (1887-1961), → Schrodinger equation, who proposed the thought experiment in 1935 in order to illustrate the inconsistency of the Copenhagen interpretation of quantum mechanics; cat, from M.E. cat, catte; O.E. catt, catte (cf. O.Fris, M.D. katte, O.H.G. kazza, Ir. cat, Welsh cath), probably from L.L. cattus, catta "cat."

Gorbé, from Mid.Pers. gurbag "cat;" → Schrodinger equation,

Schroter's effect
  اُسکر ِ شروتر   
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
  ورغه‌ی ِ شو‌آرتسشیلد   
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; → barrier.

Schwarzschild black hole
  سیه‌چال ِ شو‌آرتسشیلد   
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
  متریک ِ شو‌آرتسشیلد   
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 black hole; → metric.

Schwarzschild radius
  شعاع ِ شو‌آرتسشیلد   
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: Rs = 2GM / c2, where G is the → gravitational constant, M is the mass, and c the → speed of light. The fomula can be approximated to Rs≅ 3 x (M/Msun), in km. Therefore, the Schwarzschild radius for Sun is about 3 km and for Earth about 1 cm.

Schwarzschild black hole; → radius.

Schwarzschild singularity
  تکینی ِ شو‌آرتسشیلد   
takini-ye Schwarzschild

Fr.: singularité de Schwarzschild   

A region of infinite → space-time curvature postulated to lie within a → black hole.

Schwarzschild black hole; → singularity.

Schwarzschild solution
  لویش ِ شو‌آرتسشیلد   
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
  سنجیدار ِ شو‌آرتسشیلد   
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.

dâneš (#)

Fr.: science   

1) The study of the physical and natural phenomena, especially by using systematic observation and experiment.
2) A systematically organized body of knowledge about a particular subject. See also: → knowledge, → cognition.

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

Fr.: science fiction   

A form of fiction that draws imaginatively on scientific knowledge and speculation in its plot, setting, theme, etc. (

science; → fiction.

  دانشی، دانشیک   
dâneši, dânešik

Fr.: scientifique   

Of or pertaining to science or the sciences.
Systematic or accurate in the manner of an exact science.

From M.Fr. scientifique, from M.L. scientificus "pertaining to science," from L. scientia "knowledge," → science, + -ficus "making," from facere "to make." → -ic

Dâneši, dânešik, from dâneš, → science + -i, -ik, → ic.

scientific fact
  باشای ِ دانشی، ~ دانشیک   
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
  روش ِ دانشی   
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:
1) Observation and description of a phenomenon or group of phenomena.
2) Formulation of an hypothesis to explain the phenomena. In physics, the hypothesis often takes the form of a causal mechanism or a mathematical relation.
3) Use of the hypothesis to predict the existence of other phenomena, or to predict quantitatively the results of new observations.
4) Performance of experimental tests of the predictions by several independent experimenters and properly performed experiments.
If the experiments bear out the hypothesis it may come to be regarded as a theory or law of nature. If the experiments do not bear out the hypothesis, it must be rejected or modified. What is key in the description of the scientific method just given is the predictive power (the ability to get more out of the theory than you put in) of the hypothesis or theory, as tested by experiment. It is often said in science that theories can never be proved, only disproved. There is always the possibility that a new observation or a new experiment will conflict with a long-standing theory (Frank L. H. Wolfs, University of Rochester).

scientific; → method.

scientific notation
  نمادگان ِ دانشی، ~ دانشیک   
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 104 is the scientific notation for 35,800.

scientific; → notation.


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.

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.

susu (#)

Fr.: scintillation   

1) Rapid variation in the brightness, wavelength, and mean position of stars caused by turbulence in the Earth's atmosphere.
2) In radio astronomy, rapid fluctuations in the detected intensity of radiation from compact cosmic radio sources due to disturbances in ionized gas through which the radiation has passed. → interstellar scintillation.

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."

<< < -sc Sag sam sat sca sca Sch sci Sea sec sec see sel sem sen ser Sey Sha she sho sid sig SIM sim Sin ske sle Smi SNR sof sol sol sol sol sou sou spa spa spe spe spe sph spi spi Spo squ sta sta sta sta Ste ste ste sto str str str sub sub sub sun sup sup sup sup sur sus sym syn syz > >>