An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 13116 Search : far
K correction
  ارشایش ِ K   
aršâyeš-e K

Fr.: correction K   

A → color index correction applied to the photometric magnitudes and colors of a distant galaxy to compensate for the "reddening" of the galaxy due to → cosmological redshift. K correction is intended to derive the magnitudes in the → rest frame of the galaxy. Typically it is given as K(z) = az + bz2, where a and b depend on galaxy types. Conversely, one may deduce the redshift of a galaxy by its colors and a K-correction model.

The term K correction, probably stems from the K-term used by C. W. Wirtz (1918, Astron. Nachr. 206, 109), where K stands for Konstante, the German word for constant. The K-term was a constant offset in the redshift applied to diffuse nebulae in that epoch (source: A. L. Kinney, 1996, ApJ 467, 38); → correction.

K star
  ستاره‌ی ِ K   
setâre-ye K (#)

Fr.: étoile de type K   

An orange-red star of → spectral type K with a surface temperature of about 3600-5000 K. The spectra of K stars are dominated by the H and K lines of calcium and lines of neutral iron and titanium, with molecular bands due to cyanogen (CN) and titanium dioxide (TiO). Examples are → Arcturus and → Aldebaran.

K the letter of alphabet; → star.

K-T event
  رویداد ِ K-T   
ruydâd-e K-T (#)

Fr.: événement K-T   

Same as the → Cretaceous-Tertiary event.

K, representing the "→ Cretaceous period," and T the "→ Tertiary;" → event.

K2 mission
  گسیلان ِ K2   
gosilân-e K2

Fr.: mission K2   

A follow-up mission of the → Kepler satellite funded by → NASA. K2 provides an opportunity to continue Kepler's observations in the field of → exoplanets and expand its role into new astrophysical observations by assigning to Kepler new mission.

K, short for → Kepler spacecraft; 2, for second → mission.

Kaiser effect
  اسکر ِ کیزر   
oskar-e Kaiser

Fr.: effet de Kaiser   

The observed peculiar velocities of galaxies in the → redshift space of → galaxy clusters when the galaxies undergo → infall toward a central mass. This → redshift space distortion differs from the → fingers of God in that the peculiar velocities are not random, but correspond to the coherent falling of galaxies toward the central mass. See also → peculiar velocity.

Kaiser, N., 1987, MNRAS 227, 1; → effect.

Kant-Laplace hypothesis
  انگاره‌ی ِ کانت-لاپلاس   
engâre-ye Kant-Laplace

Fr.: hypothèse de Kant-Laplace   

The hypothesis of the origin of the solar system proposed first by Kant (1755) and later by Laplace (1796). According to this hypothesis, the solar system began as a nebula of tenuous gas. Particles collided and gradually, under the influence of gravitation, the condensing gas took the form of a disk. Larger bodies formed, moving in circular orbits around the central condensation (the Sun).

Named after the German prominent philosopher Immanuel Kant (1724-1804) and the French great mathematician, physicist, and astronomer Pierre-Simon Marquis de Laplace (1749-1827); → hypothesis.

kaon
  کاءون   
kâon

Fr.: kaon   

Any of a group of four short-lived → mesons distinguished by a → quantum number called → strangeness. Also called K meson and denoted K. They are positive, negative, or neutral and have a mass of about 495 MeV/c (about 970 times that of an → electron).

Kaon, from ka (for the letter K) + (mes)on, → meson.

kappa mechanism
  ساز-و-کار ِ کاپا   
sâzokâr-e κ

Fr.: mécanisme κ   

A process based on the effects of → opacity (κ) that drives the → pulsations of many types of variable stars. Consider a layer of material within a star and suppose that it undergoes inward contraction. This inward motion tends to compress the layer and increase the density. Therefore the layer becomes more opaque (See also → partial ionization zone). If a certain amount of flux comes from the deeper layers it gets stuck in the high κ region. The energy accumulates and heat builds up beneath it. The pressure rises below the layer, pushing it outward. The layer expands as it moves outward, cools and becomes more transparent to radiation. Energy can now escape from below the layer, and pressure beneath the layer diminishes. The layer falls inward and the cycle repeats. The κ mechanism is believed to account for the pulsations of several star families, including → Delta Scuti stars, → Beta Cephei variables, → Cepheids, and → RR Lyrae stars (See Baker & Kippenhahn, 1962, Zeitschrift für Astrophysik 54, 114). Same as κ effect and → valve mechanism. See also → gamma mechanism.

κ, the Gk. letter which denotes opacity; → mechanism.

Kardashev scale
  مرپل ِ کارداشف   
marpel-e Kardashev

Fr.: échelle de Kardashev   

A way of measuring a civilization's technological advancement based upon how much usable energy it has at its disposal. The scale was originally designed in 1964 by the Russian astrophysicist Nikolai Kardashev (who was looking for signs of extraterrestrial life within cosmic signals). It has three base classes, each with an energy disposal level: Type I, Type II, and Type III. Type I designates a civilization that is capable of controlling the total energy of its home planet (1016 watts). Type II is an interstellar civilization, capable of harnessing the total energy output of a star (1026 W). And Type III represents a galactic civilization, capable of inhabiting and harnessing the energy of an entire galaxy (1036 W). The scale has since been expanded by another four. Type 0 is civilization that harnesses the energy of its home planet, but not to its full potential. The Earth civilization is currently at about 0.73 on the Kardashev scale.

The scale was originally designed in 1964 by the Russian astrophysicist Nikolai Kardashev (1932-); → scale.

Keeler Gap
  گاف ِ کیلر   
gâf-e Keeler

Fr.: lacune de Keeler   

In the system of → Saturn's rings, the gap near the outer edge of the → A ring. It has a width of 35 km and lies at a distance of 136,530 km from the center of → Saturn.

After James A. Keeler (1857-1908); → gap.

Kellner eyepiece
  چشمی ِ کلنر   
cešmi-ye Kellner (#)

Fr.: oculaire de Kellner   

The first achromatic eyepiece consisting of a convex lens and a plano-convex lens. The convex surfaces are turned toward one another.

Named after the inventor Carl Kellner (1826-1855), a German engineer and optician; → eyepiece

kelvin (K)
  کلوین   
kelvin (#)

Fr.: kelvin   

The → SI unit of → thermodynamic temperature; symbol K. It is defined by taking the fixed numerical value of the → Boltzmann constant, k, to be 1.380 649 × 10-23 when expressed in the unit J K-1, which is equal to kg m2 s-2 K-1 , where the kilogram, meter and second are defined in terms of → Planck's constant (h), → velocity of light (c), and ΔνCs.

Named after the Scottish physicist William Thomson, also known as Lord Kelvin (1824-1907), one of the most influential scientists of the 19th century.

Kelvin scale
  مرپل ِ کلوین   
marpel-e Kelvin

Fr.: échelle de Kelvin   

A temperature scale, redefined in 1954, in which the zero point is equivalent to -273.16 °C. This fundamental fixed point, based on the → triple point of water, is considered to be the lowest possible temperature of anything in the Universe. Also known as the absolute temperature scale.

kelvin (K); → scale.

Kelvin's postulate
  فراوس ِ کلوین   
farâvas-e Kelvin

Fr.: postulat de Kelvin   

A transformation whose only final result is to transform into work heat extracted from a source which is at the same temperature is impossible. Kelvin's postulate is a statement of the → second law of thermodynamics and is equivalent to → Clausius's postulate.

kelvin; → postulate.

Kelvin-Helmholtz contraction
  ترنگش ِ کلوین-هلمهولتس   
terengeš-e Kelvin-Helmholtz

Fr.: contraction de Kelvin-Helmholtz   

The contraction of a volume of gas under its → gravity, accompanied by the → radiation of the lost → potential energy as → heat.

After the Scottish physicist William Thomson, also known as Lord Kelvin (1824-1907) and the German physicist and physician Hermann Ludwig Ferdinand von Helmholtz (1821-1894), who made important contributions to the thermodynamics of gaseous systems; → contraction.

Kelvin-Helmholtz instability
  ناپایداری ِ کلوین-هلمهولتس   
nâpâydâri-ye Kelvin-Helmholtz (#)

Fr.: instabilité de Kelvin-Helmholtz   

An → instability raised when there is sufficient velocity difference across the interface between two uniformly moving → incompressible fluid layers, or when velocity → shear is present within a continuous fluid.

Kelvin-Helmholtz contraction; → instability.

Kelvin-Helmholtz mechanism
  ساز-و-کار ِ کلوین-هلمهولتس   
sâzokâr-e Kelvin-Helmholtz

Fr.: mécanisme Kelvin-Helmholtz   

The heating of a body that contracts under its own gravity. For a large body like a planet or star, gravity tries to compress the body. This compression heats the core of the body, which results in internal energy which in turn is radiated as → thermal energy. In this way a star could be heated by its own weight.

William Thomson (Lord Kelvin) and Hermann von Helmholtz proposed that the sun derived its energy from the conversion of gravitational potential energy; → mechanism.

Kelvin-Helmholtz time
  زمان ِ کلوین-هلمهولتس   
zamân-e Kelvin-Helmholtz

Fr.: échelle de temps de Kelvin-Helmholtz   

The characteristic time that would be required for a contracting spherical cloud of gas to transform all its → gravitational energy into → thermal energy. It is given by the relation: tKH ≅ GM2/RL, where G is the → gravitational constant, M is the mass of the cloud, R the initial radius, and L the → luminosity. The Kelvin-Helmholtz time scale determines how quickly a pre-main sequence star contracts before → nuclear fusion starts. For the Sun it is 3 x 107 years, which also represents the time scale on which the Sun would contract if its nuclear source were turned off. Moreover, this time scale indicates that the gravitational energy cannot account for the solar luminosity. For a → massive star of M = 30 Msun, the Kelvin-Helmholtz time is only about 3 x 104 years.

Kelvin-Helmholtz contraction; → time.

Kennelly-Heaviside layer
  لایه‌ی ِ کنلی-هوی‌ساید   
lâye-ye Kennelly-Heaviside (#)

Fr.: couche de Kennelly-Heaviside   

One of several layers in the Earth's ionosphere occurring at 90-150 km above the ground. It reflects medium-frequency radio waves whereby radio waves can be propagated beyond the horizon.

Named after the American electrical engineer Arthur Edwin Kennelly (1861-1939) and the English physicist Oliver Heaviside (1850-1925), who independently predicted the existence of the reflecting layer in 1902; → layer.

Kepler
  کپلر   
Kepler (#)

Fr.: Kepler   

Johannes Kepler (1571-1630), a German mathematician and astronomer and a key figure in the 17th century astronomical revolution. He discovered that the Earth and planets travel about the Sun in elliptical orbits; gave three fundamental laws of planetary motion, and also did important work in optics and geometry.

<< < -es -iv -ti 21 a p abe abs abs aca acc acc acr act ada adh Adr aer aga air Alf Alg alk Alp alt alu amm ana And ang ani ano ant ant Ap apo app app Aqu Arc arg arr asc ass ast ast asy atm ato att aur aut axi B-m bad Bal bar bar Bay Bed ber Bet bif bim bin bio bis bla ble blu Bod Bol bor bou Bra Bre bro bul C-t Cal Cam can car Car Cas cat cav cel cen cer Cha cha Cha che chl Cir cir cir Cla cli clo clu co- coc coh col col col Com com com com com com com com Com con con con con con con con con con con con con coo Cor Cor cor cos cos cos Cou cou Cra Cre cri cro cub cur cyc cyl Dan dat Dav de- Deb dec dec dee def deg del Den den der det deu dew dic dif dif dil Dip dir dis dis dis dis dis diu dod Dop dou Dra dua dus dwa dyn DZ Ear ecc eco edi EHB Ein ela ele ele ele ele ell eme emp end Eng ent epi equ equ era ESP eth Eur evi exa exc exe exi exp exp ext ext ext fac fal far fec Fer fer fie fin fir fis fla Flo flu fog for for Fou fra fre fre Fro fun G s Gal gal gal Gar gau geg gen geo geo geo ger gla gly gra gra gra gra gra Gre gro GYR Had Hal hap Har HD hea hel hel Hen Her hex hig Hil hol Hoo hor hou Hub hum hyb hyd hyd hyp hys ide ign ima imp imp in- inc Ind ind ine inf inf inf ini ins ins ins int int int int Int int int int inv ion iri irr iso iso iso Jea Jor jum K c Kep Ker kin kno lab Lam Lan Lap las lat Le lef len lev lig lig lin lin lin liq Lit loc log lon lou LS lun lun Lym M s Mag mag mag mag mag mag maj man Mar mas mas mat May mea mec mel mer mes met met met mic mid mil Min Mir mix mod mod mol mon mor mov mul mur mys nan nat nav nec Nep neu New New NGC nob nom non non nor nos nuc nuc num nut obj obl obs occ oct off oli oni ope opp opt opt orb ord org orp osc out ove oxi P-w pal par par par par Pas pat pej per per per per per per pha Phe pho pho pho phy pin pla Pla pla pla pla plu poi pol pol Pol pol por pos pot Poy pre pre pre pre pri pri pri pro pro pro pro pro pro Psa pul pum Q i qua qua qua qua R A rad rad rad rad rad rad Ram Ran rat rea rea rec rec red red ref ref reg rei rel rel rem rep res res res ret rev Rho Rie ril riv rog Ros rot rul S A Sag sam sat sca sca Sch Sco Sec sec sec seg sel sem sen set Sha sha shi sho sid sig sim sin Sir ske sli Smo soc sof sol sol sol sol sou sou spa spe spe Spe spe sph spi Spi spr sta sta sta sta sta ste ste ste Sto str str sub sub sub suc sun sup sup sup sup sur swa syn syn tac tas tel tem ter tes the the the the thi thr tid til tip ton tor tou tra tra tra tra Tri tri tru tsu tur two Typ UHE ult unc uni uni uni upg ura uti val var vec Vel ver Ver vie Vir vis vis vol W-R war wav wav wea Wei wha wid win WN3 Wol wri xen yok zen zij > >>