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centimeter (cm) sântimetr (#) Fr.: centimètre A unit of length in the → metric system, equal to one-hundredth of a meter, which is the current unit of length in the → International System of Units (SI). |
Central cluster xuše-ye markazi Fr.: amas central One of the three obscured → Galactic center clusters, which contains the supermassive black hole → Sgr A*. The first stars observed in the Central cluster were evolved → massive stars showing strong He I emission lines (2.058 microns) in the near infrared K band. Subsequently more than 80 massive stars were detected including various types of → Wolf-Rayet stars, as well as → O-type and → B-type → supergiants and → dwarfs (see, e.g. Martins et al. 2007, A&A 468, 233). |
central eclipse gereft-e markazi Fr.: éclipse centrale An eclipse during which the axis of the lunar shadow cone intersects the Earth's surface (in the case of solar eclipses) or the axis of the terrestrial shadow cone intersects the Moon's surface (in the case of lunar eclipses). The total and annular solar eclipses are usually central. They can also be not central; then, they are visible only from places situated at high latitudes (M.S.: SDE). |
central force niru-ye markazi Fr.: force centrale A → force that is always directed toward a fixed point and whose → magnitude depends only on the distance from that point. Mathematically, F is a central force if and only if: F = f(r)r_{1} = f(r)r/r, where r_{1} = r/r is a unit → vector in the direction of r. If f(r) < 0 the force is said to be → attractive toward the source. If f(r) > 0 the force is said to be → repulsive from the source. In other words, a central force is one whose → potential, V(r), depends only on the → distance from the source. → Gravitational force and → electrostatic force are central, with V(r)∝ 1/r. |
central limit theorem farbin-e hadd-e markazi Fr.: théorème central limite A statement about the characteristics of the sampling distribution of means of → random samples from a given → statistical population. For any set of independent, identically distributed random variables, X_{1}, X_{2},..., X_{n}, with a → mean μ and → variance σ^{2}, the distribution of the means is equal to the mean of the population from which the samples were drawn. Moreover, if the original population has a → normal distribution, the sampling distribution of means will also be normal. If the original population is not normally distributed, the sampling distribution of means will increasingly approximate a normal distribution as sample size increases. |
Central Molecular Zone (CMZ) zonâr-e molekuli-ye markazi Fr.: zone moléculaire centrale A vast, turbulent region encircling the → Milky Way's nucleus that contains a large fraction of the → Galaxy's dense → molecular clouds and → star formation regions. Spanning -1 to +1.5 degrees of → Sgr A*, the CMZ is about 400 pc × 100 pc in size and contains at least 10^{7}→ solar masses of → giant molecular clouds, approximately 10% of the Galaxy's molecular gas. The gas in the CMZ is at higher temperature than typical giant molecular clouds and has high velocity dispersion reflecting the → turbulent nature of the gas in the area. Despite these extensive molecular reserves, the → star formation rate within the CMZ is actually lower than expected based on the analysis of nearby → star-forming regions in the quiescent → Galactic disk. A common assumption is that this is a result of the extreme conditions within the CMZ, where the density, pressure, temperature, → velocity dispersion and → radiation field are all significantly greater than elsewhere in the Milky Way (Clark et al. 2018, The Messenger 173, 22 and references therein). |
central peak setiq-e markazi Fr.: pic central The uplift of the central parts of the → crater floor due to the impacting force of a large → meteorite. The shock wave entering the Earth will first move in as a compressional wave (P-wave), but after passage of the compressional wave an expansion wave (rarefaction wave) will move back toward the surface. This will cause the floor of the crater to be uplifted and may also cause the rock around the rim of the crater to bent upward. |
central processing unit (CPU) yekâ-ye âmâyeš-e markazi Fr.: unité centrale de traitement The primary component of a → computer that processes instructions. It runs the → operating system and → applications, constantly receiving input from the user or active → software programs. The CPU has two typical components: 1) Control Unit, which extracts instructions from memory and decodes and executes them. 2) Arithmetic Logic Unit (ALU), which handles arithmetic and logical operations. → central; → processing; → unit. |
central uplift bâlâmad-e markazi Fr.: pic central Same as → central peak. |
central wavelength mowjtul-e markazi Fr.: longueur d'onde centrale 1) In an interference filter, the wavelength of peak
transmission. Central, adj. from → center; → wavelength. |
centrifugal markaz-goriz (#) Fr.: centrifuge Acting or moving in a direction away from the axis of rotation or the center of a circle along which a body is moving. From Mod.L., coined 1687 by Sir Isaac Newton from L. centri-, combining form of centrum, → center, + fugere "to run away, flee." Markaz-goriz, from markaz, → center, + goriz "running away," from gorixtan, gorizidan "to run away," Mid.Pers. virextan, proto-Iranian *vi-raik, from vi- "apart, asunder" + *raik, Av. raek- "to leave, set free, let off," Mid./Mod.Pers. reg/rig (in mordé-rig "inheritance," Skt. ric- "to leave," rinakti "gives up, evacuates," Gk. leipein "to leave," L. linquere "to leave," from PIE *linkw-, from *leikw- "to leave behind" (cf. Goth. leihvan, O.E. lænan "to lend;" O.H.G. lihan "to borrow;" O.N. lan "loan"). |
centrifugal acceleration šetâb-e markaz-goriz (#) Fr.: accélération centrifuge Of a point rotating in a circle round a central point, the outward acceleration away from the rotation axis. It corresponds to → centrifugal force. The centrifugal acceleration is given by ω x ω x r, or v^{2}/r, where ω is → angular velocity, r the distance to the rotating axis, and v the → tangential velocity. The centrifugal and → centripetal accelerations are equal and opposite. → centrifugal; → acceleration. |
centrifugal force niru-ye markaz-goriz (#) Fr.: force centrifuge A force in a rotating reference frame directed outward from the axis of rotation. → centrifugal; → force. |
centripetal markaz-gerâ Fr.: centripète Acting or moving toward a → center or → axis. → centripetal acceleration, → centripetal force. From Mod.L., coined 1687 by Sir Isaac Newton from L. centri- combining form of centrum "center" + petere "to fall, rush out;" cf. Av. pat- " to fly, fall, rush," Skt. patati "he flies, falls," Mid.Pers. patet "falls," opastan "to fall," Mod.Pers. oftâdan "to fall;" Gk. piptein "to fall," petomai "I fly;" PIE base *pet- "to fly, to rush." Markaz-gerâ, from markaz, → center, + gerâ "inclining," from gerâyidan "to incline toward;" Mid.Pers. grâyitan, → diverge. |
centripetal acceleration šetâb-e markaz-gerâ (#) Fr.: accélération centripète The rate of change of the → tangential velocity of a body moving along a circular path. The direction of centripetal acceleration is always inward along the → radius vector of the → circular motion. The magnitude of the centripetal acceleration is related to the → tangential velocity (v) and → angular velocity (ω) as follows: a_{c} = v^{2}/r = rω^{2}. According to → Newton's second law, an object undergoing centripetal acceleration is experiencing a → centripetal force. → centripetal; → acceleration. |
centripetal force niru-ye markaz-gerâ (#) Fr.: force centripète The force exerted on an object in → circular motion which is directed toward the center and keeps the body in motion. Centripetal force produces → centripetal acceleration, according to → Newton's second law: F_{c} = ma_{c}. Its direction is always inward along the → radius vector, and its magnitude is given by: F_{c}= ma_{c} = mv_{t}^{2}/r = mω^{2}r. → centripetal; → force. |
centroid markazvâr (#) Fr.: centroïde 1) Same as → center of gravity,
→ center of inertia,
→ center of mass, and
→ barycenter. |
Cepheid Kefeusi Fr.: céphéide A class of luminous, → yellow supergiants that are pulsating variables and whose period of variation is a function of their → luminosity. These stars expand and contract at extremely regular periods, in the range 1-50 days. Their highest brightness and surface temperature occur when their expansion velocity is greatest. Similarly, their minima in brightness and temperature occur when they are in the contraction phase. The longer the period, the more luminous the star. The process that drives the pulsation of → Cepheid variables is the → kappa mechanism. In fact, Cepheids provide one of the most powerful tools for measuring distances to other galaxies (→ period-luminosity relation). However, this method is limited to the distance of the → Virgo cluster of galaxies (15-20 → Mpc) even with the → HST or the largest ground-based telescopes. One particularly special Cepheid is the North Star, → Polaris. See also → RR Lyrae star. Named after the prototype → Delta Cephei discovered by John Goodricke in 1784. → Cepheus. |
Cepheid variable vartande-ye Kefeusi Fr.: variable Céphée A → variable star belonging to the class of → Cepheids. |
Cepheus Kefeus Fr.: Céphée A → constellation in the Northern Hemisphere lying next to → Cassiopeia. It contains several pulsating variable stars, including the prototype → Cepheid variable Delta Cephei. Abbreviation: Cep, genitive: Cephei. In Gk. mythology, Cepheus, king of Ethiopia, who was married to the beautiful → Cassiopeia, and was also father of princess → Andromeda. Kefeus, from Gk. Cepheus. Arabicizd form qifâvus ( |
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