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
hot pixel
  پیکسل ِ داغ   
piksel-e dâq

Fr.: pixel chaud   

Of a → CCD detector, a pixel that has higher charge loss. Hot pixels are a type of noise affecting almost every CCD camera. They are caused by small contamination or production faults in the CCD sensor area.

hot; → pixel.

hot spot
  لکه‌ی ِ داغ   
lekke-ye dâq (#)

Fr.: point chaud   

A compact, highly luminous region in a cataclysmic binary located in the accretion disk where the stream of material hits it.

hot; → spot.

hot star
  ستاره‌ی ِ داغ   
setâre-ye dâq (#)

Fr.: étoile chaude   

A member of a class of stars having high → effective temperatures (above some 15,000 K); mainly → massive stars, but also including → exciting stars of → planetary nebulae, → white dwarfs, and → symbiotic stars.

hot; → star.

sâat (#)

Fr.: heure   

The 24th part of a day; 60 minutes.
An angular unit of right ascension, equivalent to 15°.

Hour, from M.E. houre, from O.Fr. hore, from L. hora "hour, time, season," from Gk. hora "any limited time," used of day, hour, season, year; cognate E. → year.

Sâ'at, from Ar.

hour angle
  زاویه‌ی ِ ساعتی   
zâviye-ye sâati (#)

Fr.: angle horaire   

A telescope based coordinate specifying the angle, in the equatorial plane, from the meridian to a plane containing the celestial object and the north and south celestial poles.

hour; → angle.

hour circle
  پرهون ِ ساعتی، دایره‌ی ِ ~   
parhun-e sâ'ati, dâyere-ye ~

Fr.: cercle horaire   

A great circle passing through an object and the → celestial poles intersecting the → celestial equator at right angles.

hour; → circle.

hour glass
  ساعت ِ شنی   
sâat-e šeni (#)

Fr.: sablier   

A device for measuring time; it consists of a glass container having two compartments from the uppermost of which a quantity of sand runs in an hour into the lower one through a narrow tube.

Hour glass, from → hour + → glass.

Sâat-e šeni, from sâat, → hour + šeni, adj. of šen "sand."

xâné (#)

Fr.: maison   

1) A building in which people live.
2) A building for any purpose. → greenhouse.

M.E. h(o)us, from O.E. hus "dwelling, shelter, house;" cf. O.N. hus; Du. huis; Ger. Haus).

Xâné "house," from Mid.Pers. xânak, xân, xôn; cf. L. cunae "cradle;" Gk. kome "village;" Pers. Aftari dialect kiye "house, home;" PIE base *kei- "bed; to lie, to settle; beloved" (other cognates: O.E. ham "dwelling, house, village;" E. home; Ger. Heim; L. civis "townsman;" Fr. cité; E. city; Skt. śiva- "auspicious, dear").

  پرجازدن، پرجاییدن   
parjâ zadan, parjâyidan

Fr.: planer   

1) To remain in one place in the air by rapidly beating the wings.
2) Computers: To place (a pointer) over a particular area of a computer screen (such as a hyperlink on a webpage) so as to cause a pop-up box to appear or other change to occur, without clicking a button on the device.

M.E. hoveren, frequentative of hoven "hover, tarry, linger," of unknown origin.

Parjâ zadan (on the model of darjâ zadan "to march in the same place, moving one's legs up and down without going forward"), from par zadan darjâ "to beat the wings at the same place," from par zadan "to beat the wings," from par "wing, → feather," zadan, → beat, + darjâ "in the same place," from dar, → in, + , → place.


Fr.: aéroglisseur   

A vehicle capable of travelling over land or water on a cushion of air.

space; → craft.

  پرجا، پرجایش   
parjâ, parjâyeš

Fr.: vol stationnaire   

The act of one who hovers.

hover; → -ing.

Hoyle state
  حالت ِ هویل   
hâlat-e Hoyle

Fr.: état de Hoyle   

An → excited state in the → triple alpha process leading to the production of the most abundant → isotope of → carbon. The existence of this state is of extreme astrophysical importance concerning the → nucleosynthesis of 12C in stellar → cores:
4He + 4He ↔ 8Be,
8Be + 4He ↔ 12C*,
12C*12C + γ.
The process proceeds as follows. First the unstable → ground state of 8Be is formed in the collision of two → alpha particles. Since 8Be exists roughly 7 x 10-17 sec, it must fuse with an alpha particle before breaking up. However, the probability of three bodies merging simultaneously is extremely low. Hoyle showed that the 12C nucleus needs an excited state or resonance at 7.68 MeV to provide for a high reaction probability. The Hoyle state was soon found at 7.65 MeV with the predicted → spin and → parity.

In honor of the British astrophysicist Fred Hoyle (1915-2001), who predicted this state in 1953 (Hoyle et al. 1953, Physical Review 92, 1095); it was discovered by W. A. Fowler in 1957; → state.

Hubble (#)

Fr.: Hubble   

Edwin Powell Hubble (1889-1953), the American astronomer who provided the first evidence of the expansion of the Universe in 1929; → Hubble's law.

Hubble classification
  رده‌بندی ِ هابل   
radebandi-ye Hubble (#)

Fr.: classification de Hubble   

The classification of galaxies according to their visual appearance into four basic types suggested by E. Hubble: → ellipticals (E), → spirals (S), → barred spirals (SB), and → irregulars (Ir). Later on a separate class of → lenticulars (S0) was appended as an intermediate type between ellipticals and spirals. The sequence starts with round elliptical galaxies (E0). Flatter galaxies are arranged following a number which is calculated from the ratio (a - b)/a, where a and b are the major and minor axes as measured on the sky. Ellipticals are divided into eight categories (E0, E1, ..., E7). Beyond E7 a clear disk is apparent in the lenticular (S0) galaxies. The sequence then splits into two parallel branches of disk galaxies showing spiral structure: ordinary spirals, S, and barred spirals, SB. The spiral and barred types are subdivided into Sa, Sb, Sc, and SBa, SBb, SBc, respectively. Along the sequence from Sa to Sc, the central bulge becomes smaller, while the spiral arms become more and more paramount. The original, erroneous idea that such arrangement of the galaxies might represent an evolutionary sequence led to the ellipticals being referred to as early-type galaxies, and the spirals and Irr I irregulars as late-type galaxies. See also → dwarf galaxy, → dwarf elliptical galaxy, → dwarf spheroidal galaxy.

Hubble; → classification.

Hubble constant
  پایا‌ی ِ هابل   
pâyâ-ye Hubble (#)

Fr.: constante de Hubble   

The → Hubble parameter for the present epoch. It is the constant of proportionality between the → recession velocities of galaxies and their distances from each other. The latest determinations using the → Hubble Space Telescope observations of → Cepheids give H0 = 72 ± 8 km s-1 Mpc-1 (W. L. Freedman et al., 2001, ApJ 553, 47, arXiv:astro-ph/0012376), the → WMAP observations yield 70.4 ± 1.3 km s-1 Mpc-1 (N. Jarosik et al., 2011, ApJS 192, 14, arXiv:1001.4744), and the → Planck Satellite observations give 67.3 ± 1.2 km s-1 Mpc-1 (Planck Collaboration, 2014, A&A 571, A16, arXiv:1303.5076). More recently, the Hubble constant was derived by a team of astronomers, using the NASA/ESA Hubble Space Telescope, with a 2.4% accuracy (Adam G. Reiss et al., 2016, arXiv:1604.01424). The new value, 73.2 km s-1 Mpc-1, suggests that the Universe is expanding between five and nine percent faster than previously calculated. The → Hubble law is only applicable for large distances (> 20 Mpc), when the proper motions of galaxies in groups and clusters cannot confuse the recession due to expansion.

Hubble; → constant.

Hubble Deep Field (HDF)
  میدان ِ ژرف ِ هابل   
meydân-e žarf-e Hubble (#)

Fr.: champ profond de Hubble   

An image of a small region in the constellation → Ursa Major, based on the results of a series of observations by the → Hubble Space Telescope. The image was assembled from 342 separate exposures taken over ten consecutive days between December 18 and December 28, 1995. It covers an area 144 arcseconds across.

Hubble; → deep; → field.

Hubble diagram
  نمودار ِ هابل   
nemudâr-e Hubble (#)

Fr.: diagramme de Hubble   

A plot of the → redshift of galaxies against their distance or against their → apparent magnitude.

Hubble; → diagram.

Hubble distance
  دورای ِ هابل   
durâ-ye Hubble

Fr.: distance de Hubble   

The distance from the Earth to the → cosmic horizon which marks the edge of the → observable Universe. Same as → Hubble radius, → Hubble length, and → cosmic horizon.

Hubble; → distance.

Hubble flow
  تچان ِ هابل   
tacân-e Hubble

Fr.: flot de Hubble   

The general outward motion of galaxies resulting from the → expansion of the Universe.

Hubble; → flow.

Hubble law
  قانون ِ هابل   
qânun-e Hubble

Fr.: loi de Hubble   

Hubble's law.

Hubble; → law.

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