An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



<< < -ge Gal Gal gal Gar gau gel gen geo geo geo gia glo Gou gra gra gra Gre gri gui > >>

Number of Results: 394
Great Red Spot
  لکه‌ی ِ سرخ ِ بزرگ   
lakke-ye sorx-e bozorg (#)

Fr.: Grande tache rouge   

An anticyclonic storm on the planet Jupiter akin to a hurricane on Earth, but it is enormous (three Earths would fit within its boundaries) and it has persisted for at least the 400 years that humans have observed it through telescopes.

great; → red; → spot.

Great Rift
  چاک ِ بزرگ   
câk-e bozorg


An apparent fissure in the bright clouds of the Milky Way between → Cygnus and → Sagittarius caused by a series of large, dark, overlapping clouds.

great; → rift.

greatest eastern elongation
  بزرگترین درازش ِ خاوری   
bozorgtarin derâzeš-e xâvari

Fr.: plus grande élongation est   

The Greatest → elongation of an inferior planet occurring after sunset.

Superlative of → great; → eastern; → elongation.

greatest eclipse
  بزرگترین خورگرفت   
bozogtarin xorgereft

Fr.: la plus grande éclipse   

The instant when the axis of the Moon's → shadow cone passes closest to Earth's center. For → total eclipses, the instant of greatest eclipse is virtually identical to the instants of greatest magnitude and greatest duration. However, for → annular eclipses, the instant of greatest duration may occur at either the time of greatest eclipse or near the sunrise and sunset points of the eclipse path (F. Espenak, NASA).

Superlative of → great; → eclipse.

greatest western elongation
  بزرگترین درازش ِ باختری   
bozorgtarin derâzeš-e bâxtari

Fr.: plus grande élongation ouest   

The Greatest → elongation of an inferior planet occurring before sunrise.

Superlative of → great; → western; → elongation.

Greek numeral system
  راژمان ِ عددهای ِ یونانی   
râžmân-e adadhâ-ye Yunâni

Fr.: numération grecque   

A → numeral system in which letters represent numbers. In an earlier system, called acrophonic, the symbols for numerals came from the first letter of the number name. Subsequently, the numerals were based on giving values to the letters of alphabet. For example α, β, γ, and δ represented 1, 2, 3, and 4; while ι, κ, λ, and μ stood for 10, 20, 30, and 40, and ρ, σ, τ, and υ for 100, 200, 300, and 400. The Greek also used the additive principle. For example 11, 12, 13, 14, and 374 were written ια, ιβ, ιγ, ιδ, and τοδ. The numbers between 1000 and 9000 were expressed by adding a subscript or superscript ι (iota) to the symbols for 1 to 9. For example ιA and ιΘ for 1000 and 9000. Numbers greater than 9999 were expressed using M, which was the myriad, 10,000. Therefore, since 123 was represented by ρκγ, 123,000 was written as Mρκγ.

numeral; → system.

sabz (#)

Fr.: vert   

A color intermediate in the spectrum between yellow and blue (wavelength between 5000 and 5700 Å). The color of most grasses and leaves while growing.

Green, from O.E. grene, related to growan "to grow," from W.Gmc. *gronja- (cf. Dan. grøn, Du. groen, Ger. grün), from PIE base *gro- "to grow."

Sabz "green," from Mid.Pers. sabz "green, fresh," related to sabzi "grass."

green flash
  درخش ِ سبز   
deraxš-e sabz (#)

Fr.: rayon vert   

A brilliant green color that occasionally appears on the upper limb of the Sun as it rises or sets.

green; → flash.

green pea galaxy
  کهکشان ِ نخود سبز   
kahkešân-e noxod sabz

Fr.: galaxie petit pois   

A member of a class of galaxies of relatively small size having very strong emission lines especially [O iii] 5007 Å and an unusually large → equivalent width of up to 1000 Å. They were first noted because of their peculiar bright green color and small size, unresolved in Sloan Digital Sky Survey imaging. Most of the green pea galaxies are low-mass galaxies (M ~ 108.5 to 1010solar masses), with high → star formation rates (~ 10 solar masses per year), solar → metallicities, and → redshifts ranging from z = 0.112 to 0.360 (See Cardamone et al. 2009, MNRAS 399, 1191; Izotov et al. 2010, astro-ph/1012.5639).

Such called because of their appearance and green color (mainly due to very strong optical emission line [O iii] 5007 Å) in composite images; → green; pea, from M.E. pease; → galaxy.

Kahkešân, → galaxy; noxod "chick-pea," Mid.Pers. naxôd (Laki noxa, Kurd. nuk); sabz, → green.

garmxâné (#)

Fr.: serre   

A building with transparent walls and roof, usually of glass, for the cultivation and exhibition of plants under controlled conditions (

green; → house.

Garmxâné, literally "warm house," from garm, → warm, + xâné, → house.

greenhouse effect
  اُسکر ِ گرمخانه   
oskar-e garmxâné

Fr.: effet de serre   

An increase in → temperature caused when incoming → solar radiation is passed but outgoing → thermal radiation is trapped by the → atmosphere. The major factors for this effect are → carbon dioxide and → water vapor. The greenhouse effect is very important on Venus and Earth but very weak on Mars. On average, about one third of the solar radiation that hits the Earth is reflected back to space. The Earth's surface becomes warm and emits → infrared radiation. The → greenhouse gases trap the infrared radiation, thus warming the atmosphere. Without the greenhouse effect the Earth's average global temperature would be -18° Celsius, rather than the present 15° Celsius. However, human activities are causing greenhouse gas levels in the atmosphere to increase.

greenhouse; → effect.

greenhouse gases
  گاز‌های ِ دارای ِ اُسکر ِ گرمخانه   
gâzhâ-ye dârâ-ye oskar-e garmxâné

Fr.: gaz à effet de serre   

Gases responsible for the greenhouse effect. These gases include: water vapor (H2O), carbon dioxide (CO2); methane (CH4); nitrous oxide (N2O); chlorofluorocarbons (CFxClx); and tropospheric ozone (O3).

greenhouse; → gas.

Greenwich Apparent Sidereal Time (GAST)
  زمان ِ اختری ِ پدیدار ِ گرینویچ   
zamân-e axtari-ye padidâr-e Greenwich

Fr.: temps sidéral apparent de Greenwich   

The → Greenwich Mean Sidereal Time corrected for → nutation. Therefore, it is measured with respect to the → true vernal equinox. GAST and GMST differ by the → equation of the equinoxes.

Greenwich Meridian; → apparent; → sidereal; → time.

Greenwich Mean Sidereal Time (GMST)
  زمان ِ اختری ِ میانگین ِ گرینویچ   
zamân-e axtari-ye miyângin-e Greenwich

Fr.: temps sidéral moyen de Greenwich   

The → sidereal time related to the angle between the → prime meridian and the → mean vernal equinox, measured in the plane of the equator.

mean; → Greenwich Meridian; → sidereal; → time.

Greenwich Meridian
  نیمروزان ِ گرینویچ   
nimruzân-e Greenwich

Fr.: méridien de Greenwich   

The → prime meridian that separates east from west in the same way that the Equator separates north from south. It is defined by the position of the → Airy transit circle.

A borough in southeast London, England, on the Thames River. It is the site of the original Royal Observatory, through which passes the prime meridian, or longitude 0°; → meridian.

Greenwich sidereal date
  روز ِ اختری ِ گرینویچ   
ruz-e axtari-ye Greenwich

Fr.: jour sidéeal de Greenwich   

The number and fraction of → mean sidereal days elapsed on the → Greenwich meridian since 12h January 1, 4773 BC (mean sidereal).

Greenwich meridian; → sidereal; → date.

Greenwich sidereal day number
  شماره‌ی ِ روز ِ اختری ِ گرینویچ   
šomâre-ye ruz-e axtari-ye Greenwich

Fr.: nombre du jour sidéral de Greenwich   

The integral part of the → Greenwich sidereal date.

Greenwich; → sidereal; → day; → number.

Gregorian calendar
  گاهشمار ِ گرگوری   
gâhšomâr-e Gregori (#)

Fr.: calendrier grégorien   

A → solar calendar in which the year length is assumed to be 365.2425 solar days. It is now used as the civil calendar in most countries. The Gregorian calendar is a revision of the → Julian calendar instituted in a papal bull by Pope Gregory XIII in 1582. The reason for the calendar change was to correct for drift in the dates of significant religious observations (primarily Easter) and to prevent further drift in the dates.

Named after Pope Gregory XIII (1502-1585), an Italian, born Ugo Boncompagni, Pope from 1572 to 1585, who ordered the reform of the Julian calendar; → calendar.

Gregorian telescope
  دوربین ِ گرگوری، تلسکوپ ِ ~   
durbin-e Gregori, teleskop-e ~ (#)

Fr.: télescope de Gregory   

A reflecting telescope in which the light rays are reflected from the primary mirror to a concave secondary mirror, from which the light is reflected back to the primary mirror and through the central hole behind the primary mirror. Compare with the → Cassegrain telescope, in which the secondary mirror is convex.

Named after the Scottish mathematician and astronomer James Gregory (1638-1675), who devised the telescope, but did not succeed in constructing it; → telescope.

Greisen-Zatsepin-Kuzmin limit (GZK)
  حد ِ گریسن-زاتسپین-کوزمین   
hadd-e Greisen-Zatsepin-Kuzmin

Fr.: limite de Greisen-Zatsepin-Kuzmin   

A theoretical limit of approximately 6 × 1019  → electron-volts for the energy of → cosmic rays above which they would lose energy in their interaction with the → cosmic microwave radiation background photons. Cosmic ray protons with these energies produce → pions on blackbody photons via the Δ resonance according to: γCMB + p → p + π0, or γCMB + p → n + π+, thereby losing a large fraction of their energy. These interactions would reduce the energy of the cosmic rays to below the GZK limit. Due to this phenomenon, → Ultra-high-energy cosmic rays are absorbed within about 50 Mpc.

Named after Kenneth Greisen (1966), Physical Review Letters 16, 748 and Georgiy Zatsepin & Vadim Kuzmin (1966), Journal of Experimental and Theoretical Physics Letters 4, 78; → limit.

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