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spherical coordinates hamârâhâ-ye kore-yi Fr.: coordonnées sphériques A coordinate system using an origin (O) and three perpendicular axes (Ox, Oy, Oz), in which the position of a point (P) is given by three numbers (r, θ, φ). The coordinate r is the distance from the origin, θ the angle between the z-axis and the r direction, and φ the angle between the projection of r on the xy-plane and the Ox-axis. The coordinate φ is also called the → azimuthal angle. → spherical; → coordinate. |
spherical excess fozuni-ye sepehri, ~ kore-yi Fr.: excès sphérique The difference between the sum of the three angles of a → spherical triangle and 180° (π radians). |
spherical geometry hendese-ye kore-yi Fr.: géométrie sphérique The branch of geometry that deals with figures on the surface of a sphere (such as the spherical triangle and spherical polygon). It is an example of a non-Euclidean geometry. |
spherical harmonic hamâhang-e kore-yi Fr.: fonction harmonique sphérique A solution of some mathematical equations when → spherical polar coordinates are used in investigating physical problems in three dimensions. For example, solutions of → Laplace's equation treated in spherical polar coordinates. Spherical harmonics are ubiquitous in atomic and molecular physics and appear in quantum mechanics as → eigenfunctions of → orbital angular momentum. They are also important in the representation of the gravitational and magnetic fields of planetary bodies, the characterization of the → cosmic microwave background anisotropy, the description of electrical potentials due to charge distributions, and in certain types of fluid motion. The term spherical harmonics was first used by William Thomson (Lord Kelvin) and Peter Guthrie Tait in their 1867 Treatise on Natural Philosophy; → spherical; → harmonic. |
spherical latitude varunâ-ye kore-yi, ~ sepehri Fr.: latitude sphérique The angle between the → normal to a spherical reference surface and the → equatorial plane. |
spherical polar coordinate hamârâhâ-ye kore-yi-ye qotbi Fr.: coordonnées sphériques polaires Same as → spherical coordinates. → spherical; → polar; → coordinate |
spherical symmetry hamâmuni-ye kore-yi Fr.: symétrie sphérique A configuration in which the constituting parts are arranged concentrically around the center of a sphere. |
spherical triangle sebar-e kore-yi Fr.: triangle sphérique A triangle drawn on the → surface of a → sphere. A spherical triangle, like a plane triangle, may be right, obtuse, acute, equilateral, isosceles, or scalene. The sum of the angles of a spherical triangle is greater than 180° (π) and less than 540° (3π). See also → spherical excess. |
spheroid korevâr Fr.: sphéroïde A body that is shaped like a sphere but is not perfectly round, especially an ellipsoid that is generated by revolving an ellipse around one of its axes. |
spheroidal korevâr (#) Fr.: sphéroïdal Shaped like a → spheroid. |
spherule guyel Fr.: sphérule Any of many vitrified droplets of rock formed by the solidification of molten meteoritic material that flows off a meteorite during its passage through the Earth's atmosphere. Sizes range typically from 10 to 200 microns. "Small sphere," from → sphere + diminutive suffix → -ule. Guyel "small globe," from guy "ball, sphere" (variants golulé, gullé, goruk, gulu, gudé; cf. Skt. guda- "ball, mouthful, lump, tumour," Pali gula- "ball," Gk. gloutos "rump," L. glomus "ball," globus "globe," Ger. Kugel, E. clot; PIE *gel- "to make into a ball") + -el diminutive suffix, → -ule. |
Spica (α Virginis) Sonbolé (#) Fr.: Spica The brightest star in the constellation → Virgo, and the 15th brightest star in the night sky. Also known as HD 116658. It is 260 → light-years distant from Earth. A → blue giant, it is a variable → eclipsing binary, with a period of 4.014 days. Both components are → B-type stars, the → primary being a → Beta Cephei variable near to core hydrogen exhaustion (→ spectral type B1 III-IV) and the → secondary a → main sequence star (B2 V). See, e.g., R.S. Schnerr et al., 2010, arXiv:1008.4260. From L. spica "ear of grain," related to spina "thorn," corresponding to Gk. stakhys "grapes." Sonbolé, from sonbol "an ear of corn; a hyacinth," from Ar. sumbul. |
spicule sixak Fr.: spicule Any of numerous vertical → spikes of → gas visible in the → monochromatic light of certain strong → spectral lines beyond the → Sun's limb. Spicules are short-lived phenomena, corresponding to rising → jets of gas that move upward at about 30km/sec up to 10,000 km and last only about 10 minutes. From L. spiculum "spearhead, arrowhead, bee stinger," from spica "ear of grain" + -ulum, → -ule. Sixak, from six "spur, spit; thorn; any pointed thing." |
spider vane parre-ye târtan Fr.: araignée One of, usually three or four, diagonal supports that hold the → secondary mirror in a → reflecting telescope. Also called support vane. M.E. spithre, O.E. M.E. spithra, akin to spinnan "to spin;" cf. M.L.G., M.Du., M.H.G., Ger. spinne, Du. spin "spider;" → vane. Parré, → vane; târtan "spider," literally "weaver," composite word of with two cognate elements, the first one târ "thread, warp, string," related to tur "net, fishing net, snare," tâl "thread" (Borujerdi dialect), tân "thread, warp of a web," from the second element tan-, tanidan "to spin, twist, weave;" Mid.Pers. tanitan; Av. tan- to stretch, extend;" cf. Skt. tan- to stretch, extend;" tanoti "stretches," tántra- "warp; essence, main point;" Gk. teinein "to stretch, pull tight;" L. tendere "to stretch;" Lith. tiñklas "net, fishing net, snare," Latv. tikls "net;" PIE base *ten- "to stretch." |
spike sixak (#) Fr.: pointe 1) A long, pointed → metal
→ bar. M.E. spik(e) from O.N. spikr "nail;" akin to M.L.G. spiker "nail." Sixak, from six "spur, spit; thorn; any pointed thing," + -ak a suffix of similarity and nuance. |
spin espin Fr.: spin 1) Mechanics: The rotation of a body about an axis through the body.
To cause to turn around rapidly, as on an axis. To revolve or rotate rapidly, M.E. spinnen; O.E. spinnan "to draw out and twist fibers into thread" (cf. O.N., O.Fris. spinna, Dan. spinde, Du. spinnen, O.H.G. spinnan, Ger. spinnen); cognate with Pers. tan-, tanidan "to spin, twist, weave" (Mid.Pers. tanitan; Av. tan- to stretch, extend;" cf. Skt. tan- to stretch, extend;" tanoti "stretches," tántra- "warp; essence, main point;" Gk. teinein "to stretch, pull tight;" L. tendere "to stretch;" Lith. tiñklas "net, fishing net, snare," Latv. tikls "net;" PIE base *ten- "to stretch"). Espin, loan from E., as above. |
spin angular momentum jonbâk-e zâviyeyi-ye espin Fr.: moment angulaire de spin An intrinsic quantum mechanical characteristic of a particle that has no classical counterpart but may loosely be likened to the classical → angular momentum of a particle arising from rotation about its own axis. The magnitude of spin angular momentum is given by the expression S = ħ √ s(s + 1), where s is the → spin quantum number. As an example, the spin of an electron is s = 1/2; this means that its spin angular momentum is (ħ /2) √ 3 or 0.91 x 10^{-34} J.s. In addition, the projection of an angular momentum onto some defined axis is also quantized, with a z-component S_{z} = m_{s}ħ. The only values of m_{s} (magnetic quantum number) are ± 1/2. See also → Stern-Gerlach experiment. |
spin magnetic moment gaštâvar-e meqnâtisi-ye espin (#) Fr.: moment magnétique de spin The magnetic moment associated with the → spin angular momentum of a charged particle. The direction of the magnetic moment is opposite to the direction of the angular momentum. The magnitude of the magnetic moment is given by: μ = -g(q / 2m)J, where q is the charge, m is the mass, and J the angular momentum. The parameter g is a characteristic of the state of the atom. It would be 1 for a pure orbital moment, or 2 for a spin moment, or some other number in between for a complicated system like an atom. The quantity in the parenthesis for the electron is the → Bohr magneton. The electron spin magnetic moment is important in the → spin-orbit interaction which splits atomic energy levels and gives rise to → fine structure in the spectra of atoms. It is also a factor in the interaction of atom with external fields, → Zeeman effect. → spin; → magnetic moment. |
spin quantum number adad-e kuântomi-ye espin Fr.: nombre quantique de spin An integer or half-integer on which the magnitude of a particle's → spin angular momentum depends. It is expressed in units of → Planck's constant divided by 2π. Called also spin, denoted s. The spin of a particle can only have a value that is zero or a multiple of 1/2. Particles with half-integer spins, 1/2, 3/2, 5/2, ..., are → fermions. Particles with integer spin (0, 1, 2, ...) are called → bosons. |
spin temperature damâ-ye espin Fr.: température de spin The → excitation temperature of the → hyperfine structure levels of the → neutral hydrogen→ 21-centimeter line. → spin; → temperature. |
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