An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 478
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.

HRD
  نمودار ِ H-R   
nemudâr-e H-R

Fr.: diagramme H-R   

Same as → Hertzsprung-Russell diagram.

Short for → Hertzsprung-Russell diagram.

Hubble
  هابل   
Hubble (#)

Fr.: Hubble   

Edwin Powell Hubble (1889-1953), the American astronomer who provided the observational evidence of the expansion of the Universe in 1929; → Hubble-Lemaitre 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   

Hubble-Lemaitre constant.

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   

Hubble-Lemaitre flow.

Hubble; → flow.

Hubble law
  قانون ِ هابل   
qânun-e Hubble

Fr.: loi de Hubble   

Hubble-Lemaitre law.

Hubble; → law.

Hubble length
  درازای ِ هابل   
derâzâ-ye Hubble

Fr.: longueur de Hubble   

The distance traveled by light along a straight → geodesic in one → Hubble time. Also called the → Hubble radius, → Hubble distance, and → cosmic horizon.

Hubble; → length.

Hubble parameter
  پارامون ِ هابل   
pârânmun-e Hubble

Fr.: paramètre de Hubble   

Hubble-Lemaitre parameter.

Hubble; → parameter.

Hubble radius
  شعاع ِ هابل   
šo'â'-e Hubble (#)

Fr.: rayon de Hubble   

The size of the observable Universe as derived from the ratio c/H0, where H0 is the → Hubble-Lemaitre constant and c the → speed of light. Same as → Hubble distance, → Hubble length, and → cosmic horizon.

Hubble; → radius.

Hubble sequence
  پی‌آیه‌ی ِ هابل   
peyâye-ye Hubble

Fr.: séquence de Hubble   

A classification scheme in which galaxies are ordered into a sequence based on their morphology. Same as the → Hubble classification.

Hubble; → sequence.

Hubble Space Telescope (HST)
  دوربین ِ فضایی ِ هابل، تلسکوپ ِ ~ ~   
durbin-e fazâyi-ye Hubble, teleskop-e ~ ~ (#)

Fr.: télescope spatial de Hubble   

A telescope of 2.4 m in diameter, a joint NASA and ESA project, launched in 1990 into a low-Earth orbit 600 km above the ground. It was equipped with a collection of several science instruments that worked across the entire optical spectrum (from infrared, through the visible, to ultraviolet light). During its lifetime Hubble has become one of the most important science projects ever.

Hubble; → space; → telescope.

Hubble time
  زمان ِ هابل   
zamân-e Hubble (#)

Fr.: temps de Hubble   

An estimate for the age of the Universe by presuming that the Universe has always expanded at the same rate as it is expanding today. It is the inverse of the → Hubble-Lemaitre constant: tH = 1/H0. Also called the Hubble age or the Hubble period.

Hubble; → time.

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 flow
  تچان ِ هابل-لومتر   
tacân-e Hubble-Lemaître

Fr.: flot de Hubble-Lemaître   

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

Hubble-Lemaitre law; → flow.

Hubble-Lemaitre law
  قانون ِ هابل-لومتر   
qânun-e Hubble-Lamaître

Fr.: loi de Hubble-Lemaître   

The speed with which a → galaxy cluster recedes from us is directly proportional to its distance. It can be stated as v = H0d, where v is the recessional velocity, H0 the → Hubble-Lamaitre constant, and d the distance. See also → Hubble-Lemaitre flow. It should be underlined that Hubble was not the first to discover the → velocity-distance relation. Two years before Hubble, in 1927, Georges Lemaître (1894-1966) had derived the relation and published it in a paper in French which remained neglected (→ Friedmann-Lemaitre Universe).

The International Astronomical Union (IAU) at its 30th Meeting approved the Resolution B4 proposed by the IAU Executive Committee recommending the use of Hubble-Lemaitre law instead of Hubble's law, after Edwin Hubble (1889-1953), the American astronomer who published his results in 1929 and Georges Lemaître, Belgian priest and astronomer, who published a paper on the expansion of the Universe in 1927; → law.

Hubble-Lemaitre parameter
  پارامون ِ هابل-لومتر   
pârânmun-e Hubble-Lemaître

Fr.: paramètre de Hubble-Lemaître   

The rate pf change of the → cosmic scale factor: H(t) = (dR/dt)/R. The Hubble parameter is a time-dependent quantity and therefore is not constant. The → Hubble-Lemaitre constant is the Hubble-Lemaître parameter measured today.

Hubble-Lemaitre law; → parameter.

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