An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 439

Fr.: -èdre   

A combining form meaning "face" used in the names of geometrical solid figures having the form or number of faces specified by the initial element.

N.L., from Gk -edron, from hedra "seat, base, chair, face of a geometric solid," from PIE root *sed- "to → sit."

Dimé, from dim, → face.

H and K lines
  خطهای ِ H و K   
xatthâ-ye H o K

Fr.: raies H et K   

Two prominent → absorption lines, at 3968.5 Å and 3933.7 Å respectively, in the spectra of stars like the → Sun and cooler due to → singly ionized → calcium (Ca II). The strength of H and K lines can be an indication of considerable magnetic activity in the → chromosphere of these stars. The Ca II H and K lines are also common in some kinds of → eruptive variable stars. These lines are not seen in → hot stars, and start to become visible in → A-type stars.

H and K, letters of alphabet, conventionally chosen; → line.

  H I   

Fr.: H I   

Atomic or → neutral hydrogen.

From H, abbreviation of hydrogen + I "one" in Roman number system, nomenclature convention representing neutral atoms.

H I region
  ناحیه‌ی ِ H I   
nâhiye-ye H I

Fr.: région H I   

A region of neutral (atomic) hydrogen in interstellar space. At least 95 percent of interstellar hydrogen is H I. It emits radio waves that are 21 cm long.

H I; → region

  H II   

Fr.: H II   

Ionized → hydrogen, that is a proton nucleus that has lost its unique electron.

From H, abbreviation of hydrogen + II "two" in Roman number system, nomenclature convention representing singly ionized atoms.

H II galaxy
  کهکشان ِ H II   
kahkešân-e H II

Fr.: galaxie H II   

A low-mass and → metal-poor galaxy (1/30-1/3 Zsun), experiencing strong episodes of → star formation, characterized by the presence of bright → emission lines on a faint → blue continuum. The fact that H II galaxies are metal poor and very blue objects seems to suggest that they are young. Nevertheless, several studies show the existence of an → old stellar population underlying the present → star burst in most of these galaxies. This fact indicates that these objects are not young systems forming their first generation of stars. Same as → blue compact dwarf galaxy.
Spectroscopically, H II galaxies are essentially identical to the → giant H II regions found in nearby → irregular and → late-type galaxies. The correlation among structural parameters (→ H-beta → luminosity, → velocity dispersion, → linewidths) and between these parameters and the → chemical composition favors the interpretation of H II galaxies as giant H II regions in distant → dwarf irregular galaxies similar to the ones found nearby. Some examples of H II galaxies are: I Zw 18, SBS 0335-052, II Zw 33, UM 408.

H II; → galaxy.

H II region
  ناحیه‌ی ِ H II   
nâhiye-ye H II

Fr.: région H II   

A type of → emission nebulae composed of very hot gas (about 104 K), mainly ionized hydrogen, created by the ultraviolet radiation of → massive stars. H II regions originate when O or early-type stars, born in → giant molecular clouds, start heating up the cold gas, causing it to become → ionized and "glow". The effective temperatures of the → exciting stars are in the range 3 x 104 to 5 x 104 K, and throughout the nebula hydrogen is ionized. Helium is → singly ionized, and other elements are mostly singly or → doubly ionized. Typical densities in the H II region are of the order 10 to 102 cm-3, ranging as high as 104 cm-3. Internal motions occur in the gas with velocities of order 10 km s-1. The spectra of H II regions are mainly composed of strong → H Irecombination lines and → forbidden lines such as [O III], [O II], [N II]. See also → ionization-bounded H II region; → density-bounded H II region; → compact H II region; → ultracompact H II region.

H II; → region

H II region luminosity
  تابندگی ِ ناحیه‌ی ِ H II   
tâbandegi-ye nâhiye-ye H II

Fr.: luminosité de région H II   

The total number of → Lyman continuum photons emitted by an → H II region. It is usually derived using → radio continuum observations which are less affected by → interstellar extinction. The measured value is often a lower limit because of photon leakage from the H II region and absorption. See also → density-bounded H II region.

H II; → region; → luminosity.

H-âlfâ (#)

Fr.: H-alpha (Hα)   

The → Balmer series spectral line of hydrogen which results from → atomic transition between the → energy levels 2 and 3. It has a wavelength of 656.4 nm and falls in the red region of the visible spectrum.

H, symbol of → hydrogen; alpha (α), the first letter of Gk. alphabet.

H-betâ (#)

Fr.: H-beta (Hβ)   

The → Balmer series spectral line of hydrogen which results from → atomic transition between the → energy levels 2 and 4. It has a wavelength of 486.1 nm and falls in the → blue region of the → visible spectrum.

H, symbol of → hydrogen; beta (β), the second letter of Gk. alphabet.

H-R diagram
  نمودار ِ H-R   
nemudâr-e H-R

Fr.: diagramme H-R   

Same as → Hertzsprung-Russell diagram.

Short for → Hertzsprung-Russell diagram.

Habing field
  میدان ِ هابینگ   
meydân-e Habing

Fr.: champ de Habing   

A unit used to express the strength of average → far ultraviolet (FUV) intensity in the → interstellar radiation field. It is equal to 1.2 × 10-4 erg cm-2 s-1 sr-1 = 1.6 × 10-3 cm-2 s-1 = 108 photons cm-2 s-1.

Named after Harm Habing, a pioneer in this field (Habing, H. J., 1968, Bull. Astr. Netherlands 19, 421).

habitable zone (HZ)
  زُنار ِ زیست‌پذیر   
zonâr-e zistpazir

Fr.: zone habitable   

A zone around a star where the temperature would be in the range 0-100 °C to sustain liquid water on the surface of rocky planets (or sufficiently large moons). Water is thought to be a necessary component to the creation and evolution of Earth-type life. This zone depends on the parent star's luminosity and distance; it will be farther from hotter stars. A more accurate definition of HZ needs to include other factors, such as orbital → eccentricity, heat sources other than stellar irradiation, and atmospheric properties. Same as → circumstellar habitable zone; → ecosphere.

Habitable, from O.Fr. habitation, from L. habitare "to live, dwell," frequentative of habere "to have, to hold, possess," from PIE base *ghrebh- "to seize, take, hold, have, give, receive" (cf. Mod.Pers. gereftan "to take, seize;" Mid.Pers. griftan; O.Pers./Av. grab- "to take, seize;" Skt. grah-, grabh- "to seize, take," graha "seizing, holding, perceiving;" M.L.G. grabben "to grab," from P.Gmc. *grab, E. grab "to take or grasp suddenly"); → zone.

Zonâr, → zone; zistpazir, from zist, → life, + pazir "admitting, accepting, having," → -able.


Fr.: haboub   

A type of intense dust storm that blows in the deserts of North Africa and Arabia, particularly severe in areas of drought.

Haboob, from Ar. habub (هبوب) "a wind which blows hard and raises the dust."

Hadar (Beta Centauri)

Fr.: Hadar (β Centauri)   

A blue-white → giant star of → spectral type B1 III with a visual magnitude of V = 0.61 lying in the constellation → Centaurus. It lies at a distance of 350 → light-years and is the eleventh brightest star of the night sky. Also called → Agena

Hadar, from Ar. haZâr (حضار) "white camel."

hâdron (#)

Fr.: hadron   

Any elementary particle which experiences the strong nuclear force. There are two sorts of hadrons: mesons, which have zero spin, and baryons, which have spin 1/2 or 3/2.

Hadron, from Gk. hadr(os) "thick, bulky" + -on a suffix used in the names of subatomic particles (gluon, meson, neutron), quanta (photon, graviton), and other minimal entities or components (magneton).

hadron era
  دوران ِ هادرونی   
dowrân-e hâdroni

Fr.: ère hadronique   

The interval lasting until some 10-5 seconds after the Big Bang when the Universe was dominated by radiation and its temperature was around 1015 kelvins. It is preceded by → Planck era and followed by → lepton era.

hadron; → era.

hâdroni (#)

Fr.: hadronique   

Of or related to → hadrons.

hadron; → -ic.

hadronic matter
  ماده‌ی ِ هادرونی   
mâde-ye hâdroni (#)

Fr.: matière hadronique   

Ordinary matter composed of → hadrons.

hadronic; → matter.

Hafele-Keating experiment
  آزمایش ِ هافل-کیتینگ   
âzmâyeš-e Hafele-Keating

Fr.: expérience de Hafele-Keating   

An experiment performed in 1971 using four atomic → cesium clocks transported in jet airplanes eastward and westward around the Earth to verify the → time dilation predicted by the theory of → special relativity.

J.C. Hafele and R. E. Keating, 1972, Science 177, 166; → experiment.

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