Fr.: graphe raciné
Fr.: phase de rotation
Fr.: Tables rudolphines
A set of astronomical tables created in 1627 by Johannes Kepler (1571-1630) based on observations by Tycho Brahe (1546-1601). These tables allowed Kepler to derive the three laws of planetary motions bearing his name (→ Kelpler's laws). These are the first tables in which → atmospheric refraction has been taken into account. They overruled the → Prutenic Tables.
From the L. title Tabulae Rudolphinae, in memory of Rudolf II (1552-1612), king of Hungary and Bohemia, and Holy Roman Emperor; → table.
Saiph (κ Orionis)
Saiph "sword," from Ar. as-saiph al-jabbâr
Gk. skaphe "boat, skiff; a bowl."
javv-e dovomân, havâsepehr-e ~
Fr.: atmosphère secondaire
An atmosphere of a planet that forms after primordial gases had been lost or had failed to accumulate. A secondary atmosphere develops from internal volcanic outgassing, or by accumulation of material from comet impacts. It is characteristic of terrestrial planets, such as Earth, Mercury, Venus, and Mars. → primordial atmosphere.
Fr.: phase de Sedov-Taylor
The second phase in the evolution of a → supernova remnant (SNR) occurring after the → free expansion phase. After the passage of the → reverse shock, the interior of the SNR is so hot that the energy losses by radiation are very small (all atoms are → ionized, no → recombination). The expansion is driven by the → thermal pressure of the hot gas and can therefore be regarded as → adiabatic; the → cooling of the gas is only due to the → expansion. Pressure forces accelerate the swept-up → interstellar medium (ISM) converting → thermal energy (which came from original explosion) into → kinetic energy of the → shell of swept-up mass. As the mass of the ISM swept up by the shell increases, it eventually reaches densities which start to impede the free expansion. → Rayleigh-Taylor instabilities arise once the mass of the swept-up ISM approaches that of the ejected material. This causes the SNR's ejecta to become mixed with the gas that was just shocked by the initial → shock wave. The Sedov-Taylor phase lasts some 104 years and is followed by the radiative or → snowplow phase. Also called → adiabatic phase.
After Sedov, L. (1959, Similarity and Dimensional Methods in Mechanics, New York, Academic Press) and Taylor, G. I. (1950, Proc. Roy. Soc. London, A, 201, 159 and 175); → phase.
Fr.: sismographe, séismographe
Topographic description and charting of the surface of the Moon.
From seleno- combining form of Gk. selene "moon" + → -graphy.
cupân (#), šabân (#)
A person who takes care of sheep; a pastor. → shepherd moon.
From M.E. shepherde; O.E. sceaphierde, from sceap "sheep" + hierde "herder," from heord "a herd;" cf. M.L.G., M.Du. schaphirde, M.H.G. schafhirte, Ger. dial. schafhirt.
Cupân "shepherd," variants šobân, šabân; Mid.Pers. šubân, from šu + -bân. The first component from Av. pasu-, fšu- "sheep;" Mid.Pers. pâh, pasvīk "cattle;" Laki and Tâti pas "sheep;" Kurd. pez/paz; Ossetain (Digor.) fus, (Iron.) fys; Zazaki pes "small cattle;" Lâri pah; Qasrâni cu; Sogd. psw "cattle, sheep;" cf. Skt. paśu- "cattle;" L. pecu "flock, farm animals, cattle," pecunia "money, property;" Goth. faihu "money, fortune;" O.E. feoh "cattle, money;" Ger. Vieh "cattle;" Lith. pekus "cattle;" PIE base *peku- "cattle." The second component -pân/-bân a suffix denoting "keeper, guard," sometimes forming agent nouns or indicating relation, → host.
Fr.: satellites bergers
A → natural satellite in orbit near the edge of a → planetary ring, whose → gravitational force on the ring particles strongly controls the distribution of material within the ring, creating ringlets and density waves within the ring and sharp edges at ring boundaries. Examples include → Saturn's → Prometheus and → Pandora, which shepherd the narrow outer → F ring and the → Uranus satellites → Cordelia and → Ophelia and the epsilon ring. The faster-moving inside satellite accelerates the inner ring particles as it passes them, causing them to spiral out to larger orbits. At the same time the slower-moving outer satellite decelerates the outer ring particles as they pass by, causing them to spiral inward. The result is a narrow, well-defined ring.
Fr.: élément sidérophile
In the → Goldschmidt classification, any → chemical element that has an → affinity to combine with → iron rather than some other element. These elements are concentrated in the → Earth's core. The group includes → iron (Fe), → nickle (Ni), → cobalt (Co), → platinum (Pt), → gold (Au), → tin (Zn), and → tantalum (Ta). The siderophile elements include → highly siderophile element (HSE).
singular isothermal sphere
kore-ye izodamâ-ye takin
Fr.: sphère isotherme singulère
In models of star formation, an isothermal sphere in which the density distribution in the static or nearly static outer envelope obeys an r-2 power law. In the limit of infinite central concentration, the unstable equilibrium approaches the singular isothermal sphere which has the density and mass distributions ρ(r) = (a2/2πG)r-2 and M(r) = (2a2/G)r, where a is the isothermal → sound speed inside the cloud, G is the → gravitational constant, and r the distance from the center (F. H. Shu, 1977, ApJ 214, 488).
A ∩-shaped tube with unequal arms that is used to move a liquid from one level to a lower level via a third level higher than either. Once the short arm is filled, for example, by suction, the liquid flows down in the long arm under the action of gravity due to mass excess in it.
From Fr. siphon, from L. sipho (genitive siphonis), from Gk. siphon "pipe, tube," of unknown origin.
size of a graph
Fr.: taille de graphe
The number of → edges.
Fr.: spectrographe à fente
A type of spectrograph that uses a slit to provide resolution.
Smoothed Particle Hydrodynamics (SPH)
hidrotavânik-e zarrehâ-ye hamvâridé
Fr.: hydrodynamique des particules lissées
A numerical method for modeling → compressible hydrodynamic flows, which uses particles to simulate a continuous fluid flow. Because the system of hydrodynamical basic equations can be analytically solved only for few exceptional cases, the SPH method provides a numerical algorithm to solve systems of coupled → partial differential equations for continuous field quantities. The main advantage of the method is that it does not require a computational grid to calculate spatial → derivatives and that it is a Lagrangian method, which automatically focuses attention on fluid elements. The equations of motion and continuity are expressed in terms of ordinary differential equations where the body forces become classical forces between particles. This method was first independently developed by Lucy (1977, AJ 82, 1013) and Gingold & Monaghan (1977, MNRAS 181, 375).
Fr.: phase de chasse-neige
The third phase in the evolution of a → supernova remnant (SNR) occurring after the → Sedov-Taylor phase when the mass of the swept-up material becomes much larger than the amount of the ejected material. The SNR is surrounded by a cool → shell of accumulated material that is being pushed from behind, similar to what occurs for a snowplow. During this phase, → radiative cooling becomes important and the total energy is no longer conserved. Also called the → radiative phase.
solar photospheric abundance
farâvâni-ye šidsepehri-ye xoršidi
Fr.: abondance photosphérique solaire
The abundance of a → chemical element as determined from the observation of solar → spectral lines. The solar chemical composition is an important ingredient in our understanding of the formation, structure and evolution of both the Sun and our solar system. Furthermore, it is an essential reference standard against which the elemental contents of other astronomical objects are compared (Asplund et al. 2009, arXiv:0909.0948). The photospheric abundances relative to hydrogen are not representative of the → protosun, or global → solar system abundances. This is because heavy-element fractionation in the Sun has altered photospheric abundances (Lodders 2003, ApJ 591, 1220).