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: 13176 Search : in
heliosphere
  هورسپهر   
hursepehr (#)

Fr.: héliosphère   

The vast, three-dimensional region of space around the Sun filled with the → solar wind and the remnant of the → solar magnetic field carried in it. It is bounded by the → heliopause, which is estimated to be 100 → astronomical units or more from the Sun. The radius of the heliosphere is expected to vary with the → solar cycle. The heliosphere may be very elongated owing to the presence of an interstellar wind of neutral hydrogen flowing from the direction of the Galactic center.

From → helio- + → sphere.

heliostat
  هورداشتار   
hurdâštâr

Fr.: héliostat   

An instrument consisting of a mirror moved by clockwork for tracking the movement of the Sun and reflecting the sunlight into a stationary solar telescope. A heliostat is similar to a → coelostat.

Heliostat, from → helio- + -stat prefix denoting something that stabilizes, keeps, fixes, from -stata, from Gk. -states "one that causes to stand," or statos "standing," from *sta- "to stand."

Hurdâštâr, from hur-, → helio- + dâštâr "holder, maintainer," from dâštan "to hold, maintain; to have; to possess;" Mid.Pers. dâštan; O.Pers./Av. dar- "to hold, keep back, maintain, keep in mind;" cf. Skt. dhr-, dharma- "law;" Gk. thronos "elevated seat, throne;" L. firmus "firm, stable;" Lith. daryti "to make;" PIE base *dher- "to hold, support."

helium
  هلیوم   
helium (#)

Fr.: hélium   

Chemical element; symbol He; atomic number 2; atomic weight 4.0026; melting point below -272°C at 26 atmospheres pressure; boiling point -268.934°C at 1 atmosphere pressure.

Helium, from Gk. helios "sun;" cognate with Persian hur "sun", variant xor; Mid.Pers. xvar "sun;" Av. hû-, hvar- "sun;" Skt. surya-; L. sol; O.H.G. sunna; Ger. Sonne; E. sun; PIE *sawel- "sun." The element was discovered by spectroscopy during a solar eclipse in the Sun's chromosphere in 1868 by the French astronomer Pierre-Jules-Cesar Janssen (1824-1907).

helium abundance
  فراوانی ِ هلیوم   
farâvâni-ye heliom

Fr.: abondance de l'hélium   

The relative amount of helium with respect to another → chemical species, usually → hydrogen, in an astronomical object.

helium; → abundance.

helium burning
  سوزش ِ هلیوم   
suzeš-e heliyom

Fr.: combustion de l'hélium   

The stage in the evolution of a star, after the exhaustion of hydrogen, when the star produces its energy by the fusion of helium into carbon and oxygen.

helium; → burning.

helium flash
  درخش ِ هلیوم   
deraxš-e heliom (#)

Fr.: flash de l'hélium   

The sudden onset of → helium burning in the core of an → intermediate-mass star that has exhausted its hydrogen and has become a → red giant. With a → degenerate core, the temperature increases but the pressure does not. Therefore, the core cannot expand and cool, so the temperature continues to rise. When it approaches 100,000,000 K, helium will begin to fuse into carbon in the → triple alpha process. The helium flash ends the giant star's ascent of the → red giant branch. However, the violent ignition of helium in the core does not increase the star's luminosity. On the contrary, the energy released in the helium flash expands and cools the core and ultimately results in a reduction in the energy output. On the → H-R diagram the star moves down from red giant branch to the → horizontal branch, a stable state with steady helium burning in the core.

helium; → flash.

helium I
  هلیوم I   
heliom I

Fr.: hélium I   

1) The normal component of → liquid helium (4He) existing between the superfluid transition point (→ lambda point about 2.17 K) at 1 atmosphere of pressure and its boiling point of 4.2 K.
2) In stellar and interstellar plasma spectroscopy, neutral helium.

helium.

helium II
  هلیوم II   
heliom II

Fr.: hélium II   

1) A → superfluid, colder component of → liquid helium (4He), occurring when → helium I is cooled below the → lambda point.
2) 2) In stellar and interstellar plasma spectroscopy, ionized helium.

helium.

helium shell burning
  سوزش ِ پوسته‌ی ِ هلیوم   
suzeš-e puste-ye heliom

Fr.: combustion de la coquille d'hélium   

A stage in the evolution of an → asymptotic giant branch star, when all the helium in the core is fused into carbon and oxygen. No more fusion takes place in the core, and as a result the core contracts. The core contraction generates a sufficient temperature for fusing the surrounding layers of helium. Since helium shell burning is unstable, it causes → helium shell flashes.

helium; → shell; → burning.

helium shell flash
  درخش ِ پوسته‌ی ِ هلیومی   
deraxš-e puste-ye heliomi

Fr.: flash de la couche d'hélium   

A violent outburst of energy that occurs periodically in an → asymptotic giant branch star. It occurs when helium is being burnt in a thin shell surrounding the inner dense core of carbon and oxygen. → Helium shell burning is unstable, producing energy mainly in short intense flashes. The shell flash causes considerable expansion of the star followed by collapse, thus setting up deep convection. As a consequence, the → convective zone in the outer part of the star goes deeper and may → dredge-up carbon to the surface. See also → late thermal pulse; → very late thermal pulse; → AGB final thermal pulse.

helium; → shell; → flash.

helium star
  ستاره‌ی ِ هلیومی   
setâre-ye heliomi

Fr.: étoile d'hélium   

An → evolved star which has lost most or all of its hydrogen-rich envelope, leaving just a core of helium.

helium; → star.

helium-argon calibration
  کبیزش ِ هلیوم-آرگون   
kabizeš-e heliyom-ârgon

Fr.: calibration hélium-argon   

A wavelength calibration of astronomical spectra using a helium-argon light source.

helium; → argon; → calibration.

helium-argon lamp
  لامپ ِ هلیوم-آرگون   
lâmp-e heliyom-ârgon (#)

Fr.: lampe hélium-argon   

A comparison light source containing the known spectral lines of helium and Argon.

helium; → argon; → lamp.

helix
  پیچار   
picâr

Fr.: hélice   

A curve which lies on a cylinder or cone, so that its angle to a plane perpendicular to the axis is constant.

From L. helix "spiral," from Gk. helix (genitive helikos), related to eilein "to turn, twist, roll."

Picâr "that which twists," from pic, present stem of picidan "to twist, entwine, coil" + -ar agent noun suffix (on the model of parastâr, padidâr, dustâr, xâstâr).

Helix Nebula (NGC 7293)
  میغ ِ پیچار   
miq-e picâr

Fr.: Nébuleuse de l'Hélice   

A large and bright → planetary nebula in the constellation → Aquarius. Its apparent diameter is about half the size of the full Moon, corresponding to about 2.5 → light-years for a distance of about 700 light-years. It is the nearest bright planetary nebulae to Earth and one of the most spectacular examples of such objects. The Helix Nebula possibly consists of at least two separate disks with outer rings and filaments. The brighter inner disk seems to be expanding at about 100,000 km/h and to have taken about 12,000 years to form. High-resolution observations of the inner edge of the Helix's main ring have revealed thousands of cometary knots of gas with faint tails extending away from the central star. The knots have masses similar to the Earth, but are typically the size of our Solar system. The comet-like shape of the knots results from the steady evaporation of gas from the knots, produced by the strong winds and ultraviolet radiation from the central star of the nebula.The origin of the knots is currently not well understood.

helix; → nebula.

Hellas Basin
  حوضه‌ی ِ هلاس   
howze-ye Hallas

Fr.: bassin de Hallas   

One of the largest identified → impact craters both on → Mars and within the → Solar System. Hellas spans more than 2000 km across in the → southern hemisphere, a region that is much more heavily cratered and higher in average elevation than the northern hemisphere. The depth of Hellas from its bottom to its inner rim is more than 4 km. In comparison, the depth of the Grand Canyon in the United States is roughly 1.6 km, that is 2.5 times smaller! The western part of the Hellas basin contains the lowest point on Mars, about 8.2 km below the Mars datum or Martian "sea level." The formation of the impact structure is believed to have taken place in the early Noachian epoch, between 3.9 and 4.6 billion years ago (Planetary Science Institute webpage).

Hellas refers to the classical name for Greece; → basin.

helmet
  خود   
xud (#)

Fr.: casque   

1) Any of various protective head coverings worn by soldiers, policemen, firemen, etc.
2) Something resembling a helmet in form or position. → helmet streamer.

From M.Fr. helmet, diminutive of helme "helmet," from Frank. *helm (cf. O.H.G. helm "helmet"); PIE base *kel- "to cover, to hide;" cf. Av. sar- "shelter;" Laki šârd "hidden, hiddenly," šârden "to hide;" Kurd. šâr-, šârdinawa "to hide;" Skt. śárman- "cover, protection, refuge;" L. celare "to conceal;" Goth. huljan "to cover, conceal;" O.H.G. helan "to hide."

Xud "helmet," from O.Pers. xaudā- "hat, cap," tigra-xauda- "wearing the pointed cap" (as is shown in the sculpture of Skunkha the Scythian at Behistan); Av. xaoδa- "hat, cap, helmet;" Ossetic xodä; Arm. (borrowed) xoir "headband."

helmet streamer
  درفشک ِ خودوار   
derafšak-e xudvâr

Fr.: grand jet en bulbe, ~ ~ en casque prussien   

A large-scale → coronal feature with apparent → cusp, seen during a → solar eclipse. They usually arise from → sunspots and → active regions, so at the base of a helmet streamer one will often find a → prominence.  They form magnetic loops that connect the sunspots and suspend material above the surface of the Sun.  The magnetic field lines trap the material to form the streamers. The action of the → solar wind is at the origin of the peak feature.

helmet; → streamer.

Helmholtz free energy
  کاروژ ِ آزاد ِ هلمهولتس   
kâruž-e âzâd-e Helmholtz

Fr.: énergie libre de Helmholtz   

Of a system, the quantity whose decrease gives the maximum amount of external work which is performed when any physical or chemical process is carried out reversibly at constant temperature. It is defined by F = U - TS, where U is the → internal energy, T the → absolute temperature, and S the final → entropy.

After the German physicist and physician Hermann Ludwig Ferdinand von Helmholtz (1821-1894), who made important contributions to the thermodynamics of gaseous systems; → free; → energy.

Helmholtz's theorem
  فربین ِ هلمهولتس   
farbin-e Helmholtz

Fr.: théorème de Helmholtz   

A → decomposition theorem, whereby a continuous → vector field, F, can be broken down into the sum of a → gradient and a → curl term: F = -∇φ + ∇ xA, where φ is called the → scalar potential and A the → vector potential.

Helmholtz free energy; → theorem.

<< < -es -it -sc 201 951 abe abs abs aca acc acc aco act ada adh ado aer aft air Alf alg alk alp Alt alt amb ana And ang ani ann ant ant ant apo app app Apu arc arg Arn art ass ast ast ast atm ato att aur aut avo azi bac bal bar bar bat Bea Bel bet bia big bin bio Bir bla bla blo Blu bol Boo bou box bre Bri bro bur cal cal Can cap car Car cat cau cel cen cen cha Cha cha che Chi chr cir cir civ cla clo clo CMB 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 coo cor cor cor Cos cos cos cou cou cra cri cro cry cul cur cyc D l dar dat day dea dec dec dec def def deg Del Den dep der det deu dew dic dif dif dil dip dir dis dis dis dis dis diu dog Dop dou Dra Dsc dus dwa dyn Dys Ear ecc eco edg egg Ein Ela ele ele ele ele ell eme emp enc eng ent epi equ equ equ eru eth Eur eve exa exc exe exi exo exp ext ext ext fab fai Fan fea fem fer fie fil fir fir fla fli flu foc for for for fra fre fre fri fun fuz gal gal gal Gam gau Gau gen geo geo geo geo Gib glo gov gra gra gra gra gre gro Gui H-a hal Ham har Hay hea hei hel Hel her het hie hig hoa hom hor hot Hub Hug hur hyd hyd hyl 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 inv ion iro Isl iso iso Jab jet Jov Jup Kar Kep kil Kip Kra Lag Lam Lan Lar las law lea Leg Leo lev lig lim lin lin lin lit loc loc log Lor low lum lun lun Lym Mac mag mag mag mag mag mai Mal map mas mas mat Mau mea mea med Men mer Mes Met met mic mic Mie mil min Mir mix mod mol mom Moo mor mov mul mur n-b nan nat nea neg Ner neu new New NGC noc nom non non nor nor nuc nuc nul nut obj obl obs occ oct off old one ope opp opt opt orb ord org Ori osc oth ove Owl P-s Pal par par par par Pas pat pec pen per per per per per Pha pha pho pho pho phy pie pix Pla pla pla pla Pli Poi pol pol pol pol por pos pos pow pre pre pre pre pri pri pri pro pro pro pro pro pro pro pub pul pyc qua qua qua qua qui rad rad rad rad rad rad rai 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 rur S5- Sal sat sca sca Sch sci Scu sec sec sed sel sel sem seq set sha she sho sid sie sil sim sin sit sky slo sno sod sol sol sol sol son sou spa spa spe spe spe spe sph spi spo squ sta sta sta sta ste ste ste Sti sto str str sub sub sub sul sup sup sup sup sur sur syl syn sys tal Tay tel ten ter tex the the the the Tho thr tid tim Tit too Tor tra tra Tra tra Tra tri Tri tru tub tur two Typ ult ult unc uni uni uni upl 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 > >>