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.
He II line
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).
Fr.: étoile forte en hélium
An early → B-type star showing helium lines with abnormally large equivalent widths. The surface → chemical abundances of He-strong stars are influenced by the presence of a strong → magnetic field, resulting in a He overabundance that typically varies in strength over the stellar surface. Examples include HR 735, HD 184927, and CPD-62°2124.
Fr.: étoile faible en hélium
A → chemically peculiar star with very weak helium lines. Examples include 3 Sco, HD 176582, HD 217833, HR 2949, and HD 21699. The He-weak stars do not form a homogeneous group. Some of them display intense Si, or Ti and Sr lines, and are considered a hot extension of the magnetic → Ap/Bp stars. Others show overabundances of P and Ga, typically noted for → HgMn stars. The star HD 139160 belongs to the non-magnetic subgroup of He-weak stars.
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."
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.
1) A hollow muscular organ that pumps the blood through the circulatory
system by rhythmic contraction and dilation. In vertebrates there may
be up to four chambers (as in humans), with two atria and two
M.E. herte, from O.E. heorte "heart breast, soul, spirit, will, desire; courage; mind, intellect;" cf. O.Saxon herta, O.Frisian herte, O.Norse hjarta, Du. hart, O.H.G. herza, Ger. Herz; cognate with Pers. del, as below; PIE root *kerd- "heart."
Del "heart" (Pashtu z'rrah, zyah; Baluci zirde "heart, mind, soul;" Kurd. zar; Sogd. žyâwar); Mid.Pers. dil; Av. zərəd-; cf. Skt. hrd-; Gk. kardia; L. cor "heart" (Fr. cœur; Sp. corazon, It. cuore); Russ. serdtse; Arm. sirt; E. heart, as above.
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."
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.
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.
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 death of the Universe
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 of vaporization
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.
separ-e garmâyi (#), garmâ-separ
Fr.: bouclier thermique
A structure that protects against excessive heat, especially that which covers the vulnerable surfaces of a → spacecraft and protects it when re-entering the Earth's atmosphere.
Fr.: transfert de chaleur
The spontaneous transportation of heat through matter, from a region of higher temperature to a region of lower temperature.
celle-ye tâbestân (#)
Meteorology: A period of several successive days of abnormally hot and usually humid weather occurring in summer.
1) The process whereby a system's temperature increases.
The sky or Universe as seen from the Earth; the firmament. Often used in the plural.
From M.E. heven, O.E. heofon, possibly from P.Gmc. *khemina- (cf. M.L.G. heben, O.N. himinn, Goth. himins, Du. hemel, Ger. Himmel "heaven, sky"); PIE base *kem-/*kam- "to cover."
Âsmân, from Mid.Pers. âsmân "sky, heaven;" O.Pers. asman- "heaven;" Av. asman- "stone, sling-stone; heaven;" cf. Skt. áśman- "stone, rock, thunderbolt;" Gk. akmon "heaven, meteor, anvil;" Akmon was the father of Ouranos (Uranus), god of sky; Lith. akmuo "stone;" Rus. kamen; PIE base *akmon- "stone, sky." The link between the "stone" and "sky" concepts indicates that the sky had once been conceived as a stone vault by prehistoric Indo-Europeans.
Fr.: corps céleste
lâye-ye Heaviside (#)
Fr.: couche de Heaviside
English physicist Oliver Heaviside (1850-1925).