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: 3079 Search : on
Hubble constant
  پایا‌ی ِ هابل   
pâyâ-ye Hubble (#)

Fr.: constante de Hubble   

Hubble-Lemaitre constant.

Hubble; → constant.

Hubble-Lemaitre constant
  پایا‌ی ِ هابل-لومتر   
pâyâ-ye Hubble-Lemaître

Fr.: constante de Hubble-Lemaître   

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; → Friedmann-Lemaitre Universe; → constant.

Hubble-Lemaitre tension
  تنش ِ پایای ِ هابل-لومتر   
taneš-e pâyâ-ye Hubble-Lemaître

Fr.: Tension sur la constante de Hubble-Lemaître   

The discrepancy between the value of the → Hubble-Lemaitre constant inferred from a ΛCDM fit (→ Lambda cold dark matter model) to the → cosmic microwave background (CMB) and local measurements. The Universe appears to be expanding much faster now than predicted even with our latest understanding of its initial conditions and contents. Based on the → Hubble Space Telescope observations, the Hubble-Lemaitre constant is very recently estimated to be 74.03 km s-1 Mpc-1. This value indicates that the Universe is expanding at a rate about 9% faster than that implied by the → Planck satellite's observations of the → early Universe, which give a value for the Hubble constant of 67.4 km s-1 Mpc-1. For discussion, see D'Arcy Kenworthy et al. (2019, ApJ 875, 145).

Hubble-Lamaitre constant; → tension.

Hubble-Sandage classification
  رده‌بندی ِ هابل-سندیج   
radebandi-ye Hubble-Sandage

Fr.: classification de Hubble-Sandage   

Same as the → Hubble classification.

Hubble; → Hubble-Sandage variable; → sequence.

Hugoniot curve
  خم ِ هوگونیو   
xam-e Hugoniot

Fr.: courbe de Hugoniot   

A curve, on the pressure versus specific volume plane, representing the locus of all the possible states that can be reached by a substance immediately after the passage of a single → shock wave. For each initial condition there is a different curve. No combustion occurs in the process and, therefore, the chemical composition of the medium does not change. See also → Rayleigh line; → Crussard curve.

Named after the French physicist Pierre Henri Hugoniot (1851-1887), who worked on fluid mechanics, especially flow properties before and after shock waves; → curve.

Humphreys-Davidson limit
  حد ِ همفریز-دیویدسون   
hadd-e Humphreys-Davidson

Fr.: limite de Humphreys-Davidson   

An empirical upper → luminosity boundary in the → H-R diagram. It consists of two sections, a sloping part and a horizontal part. The sloping part, which decreases with decreasing → effective temperature, corresponds roughly to the → Eddington limit. The horizontal part is the temperature-independent upper luminosity limit for late-type → hypergiants. It is thought that → massive stars above the Humphreys-Davidson limit encounter an → instability, possibly due to the opacity-modified Eddington limit, and experience high → mass loss episodes which prevent their evolution to cooler temperatures. → Luminous Blue Variable stars are examples of this high mass loss phase.

Named after Roberta M. Humphreys and Kris Davidson, who first dealt with this limit (1979, ApJ 232, 409); → limit.

Huygens Division
  شکاف ِ هویگنس   
šekâf-e Huygens

Fr.: division de Huygens   

In the system of → Saturn's rings, the gap at the inner edge of the → Cassini division at a distance of 117,680 km from the center of the planet with a width of 285-400 km.

Huygens; → division.

Huygens Region
  ناحیه‌ی ِ هویگنس   
nâhiye-ye Huygens

Fr.: région de Huygens   

The inner bright part of the → Orion Nebula, from which most of the radiation is emitted. It is about 5' across corresponding to 0.7 pc (for a distance of 440 pc). See O'Dell (2001, ARAA 39, 99).

Named after the Dutch astronomer Christiaan → Huygens (1629-1695), who sketched the appearance of the Orion Nebula. His drawing, the first such known sketch, was published in Systema Saturnium in 1659. First named such by O. Gingerich (1982, Ann. NY Acad. Sci. 395, 308); → region.

hydration
  هیدرش، آبش   
hidreš, âbeš (#)

Fr.: hydratation   

The process of combining with → water.

Verbal noun of → hydrate.

hydrocarbon
  هیدروکربون   
hidrokarbon (#)

Fr.: hydrocarbure   

Any of a class of compounds containing only → hydrogen and → carbon. Hydrocarbons are organic compounds found in coal, petroleum, natural gas, and plant life. They are used as fuels, solvents, and as raw materials for numerous products such as dyes, pesticides, and plastics. Petroleum is a mixture of several hydrocarbons.

hydro- + → carbon.

hydrodynamic equation
  هموگش ِ هیدروتوانیک   
hamugeš-e hirdrotavânik

Fr.: équation hydrodynamique   

Fluid mechanics: A → partial differential equation which describes the motion of an element of fluid subjected to different forces such as pressure, gravity, and frictions.

hydrodynamic; → equation.

hydrogen bond
  بند ِ هیدروژنی   
band-e hidroženi

Fr.: liaison hydrogène   

The attractive force between the hydrogen attached to an electronegative atom of one molecule and an electronegative atom of a different molecule. Usually the electronegative atom is oxygen, nitrogen, or fluorine, which has a partial negative charge. The hydrogen then has the partial positive charge.

hydrogen; → bond.

hydrogen fusion
  ایوش ِ هیدروژن   
iveš-e hidrožen

Fr.: fusion de l'hydrogène   

A → nuclear reaction where hydrogen (H) nuclei combine to form helium (4He) nuclei. Same as the → proton-proton chain.

hydrogen; → fusion.

hydrogen ion
  هیدرون، یون ِ هیدروژن   
hidron, yon-e hidrož

Fr.: hydron, ion hydrogène   

Chemistry: The → positively charged hydrogen atom, H+, formed by removal of the orbital electron. Same as → proton.

hydrogen; → ion.

hydrogenation
  هیدروژنش   
hidroženeš

Fr.: hydrogénisation   

The process of combining or exposing to → hydrogen.

hydron
  هیدرون   
hidron (#)

Fr.: hydron   

The general name for the atomic hydrogen → cation H+.

hydro-; → -on.

hydronium
  هیدرونیوم   
hidroniom

Fr.: hydronium   

A → water, → molecule with an additional hydrogen ion (H3O+). Also called hydronium ion. Hydronium is an abundant molecular ion in the interstellar diffuse and dense molecular clouds (→ Sagittarius B2, → Orion molecular cloud OMC-1) as well as the plasma tails of → comets (→ Halley, → Hale-Bopp).

From hydr-, → hydro- + -onium a suffix used in the names of complex cations, extrcated from ammonium "ionized ammonia" (NH4+).

hydrostatic equation
  هموگش ِ هیدر-ایستاییک   
hamugeš-e hidristâik

Fr.: équation hydrostatique   

The equation describing the → hydrostatic equilibrium in a star, expressed as: dP/dr = -GMρ/r2, where P and M are the mass and pressure of a spherical shell with thickness dr at some distance r around the center of the star, ρ is the density of the gas, and G the → gravitational constant.

hydrostatic; → equation.

hyperbolic function
  کریایِ هذلولی   
karyâ-ye hozluli

Fr.: fonction hyperbolique   

Any of the six functions sinh, cosh, tanh, coth, csch, and sech that are related to the → hyperbola in the same way the → trigonometric functions relate to the → circle. Many of the formulae satisfied by the hyperbolic functions are similar to corresponding formulae for the trigonometric functions, except for + and - signs. For example: cosh2x - sinh2x = 1. See also: → hyperbolic cosine, → hyperbolic sine. Hyperbolic functions were first introduced by the Swiss mathematician Johann Heinrich Lambert (1728-1777).

hyperbolic; → function.

hyperfine transition
  گذرش ِ اَبَرنازک   
gozareš-e abar-nâzok

Fr.: transition hyperfine   

An → atomic transition involving a → hyperfine structure.

hyperfine; → transition.

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