An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 442
Hayashi forbidden zone
  زنار ِ بژکم ِ هایاشی   
zonâr-e baſkam-e Hayashi

Fr.: zone interdite de Hayashi   

The region to the right the → Hayashi track, representing objects that cannot be in → hydrostatic equilibrium. Energy transport in these objects would take place with a → superadiabatic temperature gradient.

Hayashi track; → forbidden; → zone.

Hayashi phase
  فاز ِ هایاشی   
fâz-e Hayashi

Fr.: phase de Hayashi   

A period in the → pre-main sequence evolution of a low mass star during which the star has negligible nuclear energy production and low internal temperature. Hence energy transport inside the star takes place dominantly through → convection. The star contracts homologously and evolves in the → H-R diagram along the → hayashi track with decreasing → luminosity and nearly constant → effective temperature. The time taken by a star of mass M* to contract to radius R* along a Hayashi track is of the order of the → Kelvin-Helmholtz time: tKH = 107(M*/Msun)2/(R*/Rsun)3 yr.

Hayashi track; → phase.

Hayashi temperature
  دمای ِ هایاشی   
damâ-ye Hayashi

Fr.: température de Hayashi   

The minimum → effective temperature required for a → pre-main sequence star of given mass and radius to be in → hydrostatic equilibrium. This temperature delimits the boundary of the → Hayashi forbidden zone.

Hayashi track; → temperature.

Hayashi track
  تر ِ هایاشی   
tor-e Hayashi

Fr.: trajet de Hayashi   

The path on the → Hertzsprung-Russell diagram that is followed by a fully → convective  → pre-main sequence star to reach the → zero-age main sequence. Hayashi tracks for → low-mass stars are near vertical. At higher masses, stars become increasingly radiative as they contract and the Hayashi tracks are almost horizontal.

Named after the Japanese astrophysicist Chushiro Hayashi (1920-2010), who published his paper in 1961 (PASJ 13, 450); → track.


Fr.: hasard, risque, danger   

1) A danger that one can foresee but cannot avoid.
2) Something causing unavoidable danger, peril, risk, or difficulty.
3) The absence or lack of predictability; chance; uncertainty (

M.E. hasard, from O.Fr. hasard, hasart "game of chance played with dice," possibly from Sp. azar "an unfortunate card or throw at dice," postulated to derive from Ar. az-zahr "the die," but this etymology is controversial.

Âpé, from Av. au-pat-, "to fall down, off," from pat- "to fall, fly;" Proto-Ir. *pat- "to fall; fly; rise;" related to Pers. oftâdan "to fall; to befall; to happen," → fall. Pers. âfat "blight, pest, curse," may belong to this family.


Fr.: dangereux   

1) Full of risk; perilous; risky.
2. Dependent on chance (

Adj. from → hazard.

nezm (#)

Fr.: brume sèche   

A phenomenon where fine particles of → dust and/or → smoke suspended in the → atmosphere near Earth reduce the → visibility by → scattering light.

Maybe from M.E. *hase, O.E. hasu, variant of haswa "ashen, dusky."

Nezm "mist, fog, vapor."

HD 5980
HD 5980

Fr.: HD 5980   

A remarkable → binary star system composed of → massive stars that is associated with NGC 346, the largest → H II region + OB star cluster in the → Small Magellanic Cloud. HD 5980 is a rather complex system because it consists of at least three stars: two stars form an → eclipsing binary with a period of 19.266 days, while the third component, an → O star, is detected by means of a set of absorption lines. Whether or not the third star is physically bound to the eclipsing binary remains currently unclear. HD 5980 underwent an → LBV-type event in August 1994. Before the LBV eruption, both components of the eclipsing binary already showed emission lines in their spectra and were thus classified as → Wolf-Rayet stars. However, as shown by the analysis of the spectra taken during and after the LBV event, at least the star that underwent the eruption was not a classical, helium-burning, Wolf-Rayet object, but rather a WNha star. This means a rather massive star with substantial amounts of hydrogen present in its outer layers. These WNha stars have → stellar wind properties that are intermediate between those of extreme → Of stars and classical → WN Wolf-Rayet stars.

Henry Draper system; → number.

HD 93129
HD 93129

Fr.: HD 93129   

A multiple → O-type star in the → Trumpler 14 cluster, which consists of at least three components. The main component, HD 93129A, is of spectral type O2 If*, a very rare hot star and the closest known O2 star (Walborn et al. 2002). It is one of the most luminous stars known. HD 93129B, lying 2.7 arcsec apart, is an O3.5 V((f+)) type. Recent → HST observations have shown that component A is itself probably a double or → binary star with a separation of 0.055 arcsec.

HD number.

HD 97950
HD 97950

Fr.: HD 97950   

The core of the Galactic → giant H II region, → NGC 3603. It is a multiple object composed of several → massive stars with a collective → spectral type of around WN6+O5. One of the stars, → NGC 3603A-1, is a double-eclipsing binary with an orbital period of 3.77 days. The component masses are 116 Msun for the primary and 89 Msun for the secondary, respectively. The primary WN6ha component of A1 is the most massive star ever directly weighed. A second star, C, has newly been identified, which has been classified as an SB1 binary, and in which only the primary (WN6ha) component is visible. The third star, B, shows constant radial velocities over the observed time interval, and therefore is most likely not a binary. While the primary component of C might have a mass similar to or even greater than that of A1's primary, it is possible that star B, be the most massive member in NGC 3603 and, therefore, the most massive main-sequence star known in the Galaxy (Schnurr et al., 2008, MNRAS, 389, L38).

HD number.

HD number
  عدد ِ HD   
adad-e HD (#)

Fr.: numéro HD   

An identifying number assigned to the stars in the Henry Draper catalog. For example, the star Vega is HD 172167.

Henry Draper system; → number.

He II line
  خط ِ He II   
xatt-e He II

Fr.: raie He II   

Any of the → spectral lines arising from → singly ionized helium in the atmosphere of → O-type and → Wolf-Rayet stars. He II lines are chiefly in absorption, but some of them, such as 4686 Å occur in emission in hotter stars. The presence of He II → absorption lines separates O types from → B-type stars. A number of these He II lines belong to the → Pickering series involving transitions with → principal quantum numbern = 4 and higher. Although the n = 3-4 (4686 Å) transition also belongs to ionized helium and often occurs in these hot stars, it does not belong to the Pickering series because it has a lower landing level quantum number (n = 3). The same goes for n = 2-5 (4026 Å).

helium; → line.

sar (#)

Fr.: tête   

1) That part of anything that forms or is situated at the top, summit, or upper end.
2) The → nucleus and surrounding → coma of a → comet.

Head, from O.E. heafod "top of the body," also "chief person" (cf. O.S. hobid; Goth. haubiþ Ger. Haupt "head"), from PIE *kauput- "head;" cf. Skt. kaput-, kapala- "skull;" L. caput "head;" Pers. dialect Lori: kapu "head," kapulek "skull, middle of the head;" Kurd. kapol "skull;" Pashto kaparay "skull."

Sar "head," soru, sorun "horn" (karnâ "a trumpet-like wind instrument," variant sornâ "a wind instrument"); Mid.Pers. sar "head," sru "horn;" Av. sarah- "head," srū- "horn, nail;" cf. Skt. śiras- "head, chief;" Gk. kara "head," karena "head, top," keras "horn;" L. cornu "horn," cerebrum "brain;" P.Gmc. *khurnaz (Ger. Horn, Du. horen; cognate with E. horn, as above, from PIE *ker- "head, horn;" O.E. horn "horn of an animal," also "wind instrument;" E. horn); PIE base *ker- "head, horn, top, summit."

head-tail galaxy
  کهکشان ِ \"سر-دم\"   
kahkešân-e sar-dom

Fr.: galaxie tête-queue, ~ têtard   

A member of the class of radio galaxies (→ radio galaxy) that have a strong radio emission coming from a bright "head" and a more diffuse emission from a "tail." They are often found in clusters.

head; → tail; → galaxy.

garmâ (#)

Fr.: chaleur   

Energy possessed by a substance in the form of kinetic energy of atomic or molecular translation, rotation, or vibration.

Heat, from O.E. hætu, hæto, from P.Gmc. *khaitin- "heat," from *khaitaz "hot" (cf. O.N. hiti, Ger. hitze "heat," Goth. heito "fever").

Garmâ "heat, warmth," from Mid.Pers. garmâg; O.Pers./Av. garəma- "hot, warm;" cf. Skt. gharmah "heat;" Gk. thermos "warm;" L. formus "warm," fornax "oven;" P.Gmc. *warmaz; O.E. wearm; E. warm; O.H.G., Ger. warm; PIE *ghworm-/*ghwerm- "warm."

heat capacity
  گنجایش ِ گرمایی   
gonjâyeš-e garmâyi (#)

Fr.: capacité thermique, ~ calorifique   

The ratio of an amount of heat, dQ, transferred to a body in some process to the corresponding change in the temperature of the body: C = dQ/dT. The heat capacity depends upon the mass of the body, its chemical composition, thermodynamic state, and the kind of process employed to transfer the heat. The word "capacity" may be misleading because it suggests the essentially meaningless statement "the amount of heat a body can hold," whereas what is meant is the heat added per unit temperature rise. → specific heat.

heat; → capacity.

heat conduction
  هازش ِ گرما   
hâzeš-e garmâ

Fr.: conduction de chaleur   

A type of → heat transfer by means of molecular agitation within a material without any motion of the material as a whole.

heat; → conduction.

heat convection
  همبز ِ گرما   
hambaz-e garmâ (#)

Fr.: convection de chaleur   

A type of → heat transfer involving mass motion of a fluid such as air or water when the heated fluid is caused to move away from the source of heat, carrying energy with it.

heat; → convection.

heat death of the Universe
  مرگ ِ گرمایی ِ گیتی   
marg-e garmâyi-ye giti (#)

Fr.: mort thermique de l'Univers   

Assuming that the Universe is a thermodynamically → isolated system, a state of absolute uniformity in the Universe in which all temperature differences would reduce to zero and no energy will be available for use, according to the → second law of thermodynamics. In that condition of maximum → entropy, the Universe would be in a state of unchanging death. First introduced by the German physicist Hermann von Helmholtz (1821-1894) in 1854, on the basis of William Thomson's (1824-1907) idea.

heat; → death; → Universe.

heat of vaporization
  گرمای ِ بخارش   
garmâ-ye boxâreš

Fr.: chaleur de vaporisation   

The amount of heat energy required to transform an amount of a substance from the liquid phase to the gas phase. → molar heat of vaporization.

heat; → vaporization.

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