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.
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).
Greenwich Apparent Sidereal Time (GAST)
zamân-e axtari-ye padidâr-e Greenwich
Fr.: temps sidéral apparent de Greenwich
Greenwich Mean Sidereal Time (GMST)
zamân-e axtari-ye miyângin-e Greenwich
Fr.: temps sidéral moyen de Greenwich
Fr.: méridien de Greenwich
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
ruz-e axtari-ye Greenwich
Fr.: jour sidéeal de Greenwich
Greenwich sidereal day number
šomâre-ye ruz-e axtari-ye Greenwich
Fr.: nombre du jour sidéral de Greenwich
The integral part of the → Greenwich sidereal date.
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.
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)
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.
1) A → grating of crossed bars; gridiron.
Shortening of gridiron "a utensil consisting of parallel metal bars on which to broil meat or other food," from M.E. griderne, from gridel, from O.Fr. gredil, gridil, from L. craticula "gridiron, small griddle," diminutive of cratis "wickerwork."
Šabâk, from Laki šowâk "a net woven from goat fleece used for carrying chaff or fruits like melon," variants šâvâk (Lori), šavak (Nahâvand).
Grinding, verbal noun of grind, from O.E. grindan, forgrindan "destroy by crushing," from P.Gmc. *grindanan (cf. Du. grenden), from PIE *ghrendh- "crushing" (cf. L. frendere "to crush, grind;" Gk. khondros "granule, groats").
Sâbeš, verbal noun of sâbidan, variants sâyidan, pasâvidan "to touch" (Khotanese sauy- "to rub;" Sogdian ps'w- "to touch;" Proto-Iranian *sau- "to rub").
An optical dispersing device used in a spectrograph. It is a combination of a prism and a grating, in the sense that the grating is placed side by side to one surface of a small-angle prism.
Grism, from gr(ating) + (pr)ism.
Fr.: grain abrasif
Abrasive particles or granules, classified into predetermined sizes, typically of Silicon Carbide or Aluminum Oxide, used between the mirror and tile tool to grind the glass.
Grit, from O.E. greot "sand, dust, earth, gravel," from P.Gmc. *greutan "tiny particles of crushed rock" (cf. O.S. griot; O.N. grjot "rock, stone;" Ger. Grieß "grit, sand"); PIE base *ghreu- "to rub, pound, crush."
Šen "sand, grit."
An instrument composed of a vertical staff and a horizontal cross with a plumb line at the end of each arm. It was used in ancient Roman empire to survey straight lines, squares, and rectangles.
From L. groma, gruma, from Gk. → gnomon, possibly through Etruscan.
Fr.: trait, sillon
Groove, from O.N. grod "pit," or M.Du. groeve "furrow, ditch," from P.Gmc. *grobo (cf. O.H.G. gruoba "ditch," Goth. groba "pit, cave," O.E. græf "ditch"), related to grave (n.).
Šiyâr "furrow, ploughed ground," from Av. karši-, karša- "furrow," karšuiiā "plowed (land)," related to Mod.Pers. kašidan/kešidan "to carry, draw, protract, trail, drag;" Mid.Pers. kešidan "to draw, pull;" from Av. karš- "to draw; to plow;" cf. Skt. kars-, kársati "to pull, drag, plough," karṣū- "furrow, trench;" Gk. pelo, pelomai "to be in motion, to bustle;" PIE base kwels- "to plow."
1) zamin; 2) zaminé (#)
Fr.: sol, terrain
1) The surface of the Earth; soil.
From O.E. grund "foundation, ground, surface of the earth," from P.Gmc. *grundus (cf. Du. grond, Ger. Grund "ground, soil, bottom").
1) Zamin, variant
zami "earth, ground," from Mid.Pers. zamig "earth;"
Av. zam- "the earth;" cf. Skt. ksam; Gk. khthôn, khamai
"on the ground;" L. homo "earthly being" and humus
"the earth" (as in homo sapiens or homicide, humble, humus, exhume);
PIE root *dh(e)ghom "earth."
hâlat-e zaminé (#)
Fr.: état fondamental
The lowest energy state of an atom, molecule, or ion, when all electrons are in their lowest possible energy levels, i.e. not excited.
nepâheš az zamin
Fr.: observation au sol
An astronomical observation carried out using a telescope on Earth, as opposed to that from an orbiting satellite.
1) goruh (#); 2) goruhândan; goruhidan
Fr.: 1) groupe; 2) grouper; se grouper
1a) Any collection or assemblage of persons or things considered together or
regarded as belonging together; e.g.
→ Local Group of galaxies.
From Fr. groupe "cluster, group," from It. gruppo "cluster, packet, knot," likely from P.Gmc. *kruppa "round mass, lump."
Goruh "group," from Mid.Pers. grôh "group, crowd."