<< < -sc Sag sam sat sca sca Sch sco sec sec sec sei sel sem sep sex Sha she sho sid sig sim sin Sir sky slo sno sof sol sol sol sol sou Sou spa spe spe spe sph spi spi spr sta sta sta sta ste ste ste Sto str str Sty sub sub suf sun sup sup sup sup sur sym syn sys > >>
sphere of influence sepehr-e hanâyeš Fr.: sphère d'influence The region of space around one of the bodies in a system of two celestial bodies where a third body of much smaller mass is influenced by the gravitational field of that body. The sphere of influence of a planet with respect to the Sun has a radius given by: R = R_{P}(M_{P}/M_{S})^{2/3}, where R_{P} is the radius of the planet's orbit around the Sun, M_{P} is the mass of the planet, and M_{S} is the solar mass. The sphere of influence of the Earth has a radius of about 927,000 km or slightly under 150 Earth radii. Beyond this limit, a space probe will come under the influence of the Sun. |
spheres of Eudoxus sepehrhâ-ye Eudoxus Fr.: sphères d'Eudoxe A series of spheres with varying radii centred on the Earth, each rotating uniformly about an axis fixed with respect to the surface of the next larger sphere, all comprising a model in Greek astronomy to describe the motions of the heavenly bodies. The spheres turned with different speeds about axes with different orientations. The fixed stars revolved around the Earth by the motion of the most distant sphere to which the stars were thought to be attached. Each of the five planets' (Mercury, Venus, Mars, Jupiter, and Saturn) motion could be described using four spheres. The Sun and the Moon required three spheres each to explain their motions. Therefore, a total of 27 spheres described the behavior of the heavenly bodies in terms of circular motion. Eudoxus was the first person to devise a model that could explain the → retrograde motion of the planets in the sky along a looped curve known as the → hippopede. → sphere; Eudoxus (Ευδοξοσ) of Cnidus (c 408 BC - c 355 BC), Greek astronomer and mathematician. |
spherical kore-yi Fr.: sphérique Having the form of a sphere; of or pertaining to a sphere or spheres. |
spherical aberration birâheš-e koreyi Fr.: aberration sphérique, ~ de sphéricité An aberration of a spherical lens or mirror in which light rays converge not to a single point but to a series of points with different distances from the lens or mirror. Spherical aberration is corrected by using parabolic reflecting and refracting surface → spherical; → aberration. |
spherical angle zâviye-ye koreyi Fr.: angle sphérique An angle formed on the surface of a sphere by the intersection of two great circles of the sphere. |
spherical astrolabe ostorlâb-e sepehri, ~ kore-yi Fr.: astrolabe sphérique A type of → astrolabe in which the observer's horizon is drawn on the surface of a globe, mounted with a freely rotating spherical lattice work or 'spider' representing the celestial sphere. The earliest description of the spherical astrolabe dates back to the Iranian astronomer Nayrizi (865-922). |
spherical astronomy axtaršenâsi-ye kore-yi Fr.: astronomie sphérique The branch of astronomy that is concerned with determining the apparent positions and motions of celestial bodies on the celestial sphere. Same as → positional astronomy. |
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." |
<< < -sc Sag sam sat sca sca Sch sco sec sec sec sei sel sem sep sex Sha she sho sid sig sim sin Sir sky slo sno sof sol sol sol sol sou Sou spa spe spe spe sph spi spi spr sta sta sta sta ste ste ste Sto str str Sty sub sub suf sun sup sup sup sup sur sym syn sys > >>