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: 13048 Search : far
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.

Kepler problem
  پراسه‌ی ِ کپلر   
parâse-ye Kepler

Fr.: problème de Kepler   

1) Given the trajectory of a particle moving in a → central force field, determine the law governing the central force.
2) Inversely, considering a central force -k/r2, determine the trajectory a particle moving in the field will take.

Kepler; → problem.

Kepler spacecraft
  تلسکوپ ِ فضایی ِ کپلر   
teleskop-e fazâyi-ye Kepler

Fr.: télescope spatial de Kepler   

A → NASA space telescope launched in March 2009 to discover Earth-size planets using the → transit method. The telescope has a diameter of 0.95 m and its only instrument is a → photometer that continuously monitors the brightness of over 145,000 → main sequence stars in a fixed field of view of 115 deg2 (about 12° diameter). The expected mission lifetime is 3.5 years extendible to at least 6 years.

In honor of Johannes → Kepler; → spacecraft.

Kepler's equation
  هموگش ِ کپلر   
hamugeš-e Kepler

Fr.: équation de Kepler   

An equation that enables the position of a body in an elliptical orbit to be calculated at any given time from its orbital elements. It relates the → mean anomaly of the body to its → eccentric anomaly.

Keplerian, adj. of → Kepler; → equation.

Kepler's first law
  قانون ِ نخست ِ کپلر   
qânun-e naxost-e Kepler (#)

Fr.: première loi de Kepler   

Planets move in elliptical paths, with the Sun at one focus of the ellipse (year 1609).

Kepler; → first; → law.

Kepler's laws
  قانون‌های ِ کپلر   
qânunhâ-ye Kepler (#)

Fr.: lois de Kepler   

1) The planets move about the Sun in ellipses, at one focus of which the Sun is situated.
2) The → radius vector joining each planet with the Sun describes equal areas in equal times.
3) The ratio of the square of the planet's period of revolution to the cube of the planet's mean distance from the Sun is the same for all planets.

Kepler; → law.

Kepler's second law
  قانون ِ دوم ِ کپلر   
qânun-e dovom-e Kepler (#)

Fr.: deuxième loi de Kepler   

A line joining a planet to the Sun sweeps out equal areas in equal intervals of time (year 1609).

Kepler; → second; → law.

Kepler's star
  ستاره‌ی ِ کپلر   
setâre-ye Kepler (#)

Fr.: étoile de Kepler   

A → supernova in → Ophiuchus, first observed on 1604 October 9, and described by Johannes Kepler in his book De stella nova (1606). It reached a maximum → apparent magnitude of -3 in late October. The star remained visible for almost a year. The → light curve is that of a → Type Ia supernova. The → supernova remnant consists of a few filaments and brighter knots at a distance of about 30,000 → light-years. It is the radio source 3C 358. Also known as SN 1604 and Kepler's supernova.

Kepler; → star.

Kepler's third law
  قانون ِ سوم ِ کپلر   
qânun-e sevom-e Kepler (#)

Fr.: troisième loi de Kepler   

The ratio between the square of a planet's → orbital period (P) to the cube of the mean distance from the Sun (a) is the same for all planets: P2a3 (year 1618). More accurately, P2 = (4π2a3) / [G(M1 + M2)], where M1 and M2 are the masses of the two orbiting objects in → solar masses and G is the → gravitational constant. In our solar system M1 = 1. The → semi-major axis size (a is expressed in → astronomical units and the period (P) is measured in years.

Kepler; → third; → law.

Keplerian
  کپلری   
Kepleri

Fr.: keplerien   

Of or pertaining to Johannes Kepler or to his works or discoveries.

From → Kepler + -ian a suffix forming adjectives.

Keplerian angular velocity
  تندای ِ زاویه‌ای ِ کپلری   
tondâ-ye zâviye-yi-ye Kepleri

Fr.: vitesse angulaire keplérienne   

The angular velocity of a point in a circular orbit around a central mass. It is given by: ΩK = (GM/r3)1/2, where G is the → gravitational constant, M is the mass of the gravitating object, and r is the radius of the orbit of the point around the object.

Keplerian; → angular; → velocity.

Keplerian disk
  گرده‌ی ِ کپلری، دیسک ِ ~   
gerde-ye Kepleri, disk-e ~

Fr.: disque keplérien   

A circumstellar disk (such as an → accretion disk or a → protoplanetary disk) in which the → angular velocity at each radius is equal to the angular velocity of a circular → Keplerian orbit at the same radius. The main characteristic of the Keplerian disk is that → orbital velocity varies as r-1/2. This means that an object on an orbit closer to the central mass turns more rapidly than that on a farther orbit. This velocity difference is at the origin of internal friction or kinematic viscous forces between disk particles, which heats up the material.

Keplerian; → disk.

Keplerian orbit
  مدار ِ کپلری   
madâr-e Kepleri (#)

Fr.: orbit keplérienne   

The orbit of a spherical object of a finite mass around another spherical object, also of finite mass, governed by their mutual → gravitational forces only.

Keplerian; → orbit.

<< < -es -iv -ti 21 a p abe abs abs aca acc acc acr act ada adh Adr aer AGB air Alf Alg all alp alt AM amo ana And ang ani ano Ant Ant apa apo app app Ara Arc ari Arr ash ass ast ast asy atm ato att aut ave axi Bab bal Bal bar bar bea Bek Bes bia Big bin bin bip biv bla bli blu Boh Bol Bos bou bra bri bro buo cal cal can cap car Car cat cat CCD Cen cen CH cha cha che Che chr cir cir cit cla clo clo clu Coa coe 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 Cop Cor cor cor cos cos cou cou Cow cre cri cro cry cur cya Cyg dan dar dat de- deb dec dec ded def deg del dem den dep des det dev dia dif dif dih dio Dir dis dis dis dis dis dis DO don dou dow dro dur dwa dyn Dys ear ebb ecl edg egg Ein Ela ele ele ele ele ell eme emp enc eng ent epi equ equ equ esc eth Eur Eve exa exc exe exi exp exp ext ext ext fac fal far fed Fer fer fie fin fir fis fla flo flu fol for for fou fra fre Fre fro fut G-t gal gal gam gas Gau Gem gen geo geo geo gia Gli Gol gra gra gra gra gre gri gui H I Hag hal har hat He- hea hel Hel her Hes hie hig his hom hor hot Hub Hug hur hyd hyd hyg hyp ice ide ima Ima imp imp inc inc ind ine inf inf inf ing inn ins ins int int int int int int int int inv Io ion iro isl iso iso Jac jet jud jur Kel Kep kil Klo Kui Lag lam Lap Lar lat law lea len lep Lib lig lim lin lin Lio lit loc LOF lon Lor low lum lun Lup Lyo mac mag mag mag mag mag mai man Mar mas mas mat Max mea mec Meg Mer Mer met met Met mic Mid Mil min Mir mit mod mod mol mon Mor mou mul mul mys nan Nat nau nec neo neu nev New NGC no nom non non nor not nuc nuc num nut obj obs obs occ ocu oft ome Oor ope opp opt opt orb ord ori ort osc out ove oxi pai pan par par par par pas pea pen per per per per Per per pha phi pho pho pho phy pio Pla pla pla pla Pla plu Poi pol pol pol poo pos pos pot pra pre pre pre pre pri pri pro pro pro pro pro Pro pro pse pul pur qua qua qua qua que rac rad rad rad rad rad rad ran rar ray rea rea rec rec red red ref ref reg rel rel rel ren res res res res ret rev Ric rig rin roc roo rot rot Rus Sac sal sat sca sca Sch sci Scu sec sec Sed sel Sel sen ser Sex Sha she sho sid sig sil sim sin siz sla Sma sno sof sol sol sol sol sou sou spa spa spe spe spe sph spi spi spr squ sta sta sta sta ste ste ste Sto Str str str sub sub suc sun sup sup sup sup sur swa syn syn tab tar tek tem ter tes the the the the Tho thr tid tim Tis Too Tor tra tra Tra tra tra tri tri tru Tul tur two Typ ult un- und uni uni unk upp Urc utt val var vec vel ver vib vio vir vis voi vor wan wat wav wax wea Wei whi Wil win WN9 wor X-r yel you zer zod > >>