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: 13116 Search : far
atmospheric emission
  گسیل ِ جوی   
gosil-e javvi

Fr.: émission atmosphérique   

The emission of electromagnetic radiation from the atmosphere due to thermal and → non-thermal processes. → Thermal emission comes mainly from → water vapor. Non-thermal processes result in emission lines oxygen (optical) and OH (near-IR). Atmospheric emission is a very significant source of noise in astronomical observations. See also → airglow, → aurora.

atmospheric; → emission.

atmospheric extinction
  خاموشی ِ جوی   
xâmuši-ye javvi

Fr.: extinction atmosphérique   

The decrease in the intensity of light from a celestial body due to absorption and scattering by Earth's atmosphere. It increases from the zenith to the horizon and affects short wavelengths more than long wavelengths, so that objects near the horizon appear redder than they do at the zenith.

atmospheric; → extinction.

atmospheric muon
  موءون ِ جوی، ~ هواسپهری   
muon-e javvi, ~ havâsepehri

Fr.: muon atmosphérique   

A → subatomic particle produced when → primary cosmic rays, impinge on the Earth's atmosphere producing a particle cascade, in which secondary particles decay into → muons. In the energy range up to 100 → GeV atmospheric muons come mostly from the decay of secondary → pions: π±→ μ± + anti-νμ. At higher energies, the → kaon contribution to the muon flux become significant, reaching the asymptotic value of 27% at about 10 TeV: K±→ μ± + anti-νμ.

atmospheric; → muon.

atmospheric neutrino
  نوترینو‌ی ِ جوی   
notrino-ye javvi

Fr.: neutrino atmosphérique   

A neutrino produced in the collision of → cosmic rays (typically → protons) with nuclei in the → upper atmosphere. This creates a shower of → hadrons, mostly → pions. The pions decay to a → muon and a muon neutrino. The muons decay to an → electron, another muon neutrino, and an electron neutrino.

atmospheric; → neutrino.

atmospheric noise
  نوفه‌ی ِ جوی   
nufe-ye javvi

Fr.: bruit atmosphérique   

Noise in radio wavelengths caused by natural atmospheric processes, mainly lightening discharges in thunderstorms. They can affect radio observations.

atmospheric; → noise.

atmospheric refraction
  شکست ِ جوی   
šekast-e javvi

Fr.: réfraction atmosphérique   

The shift in apparent direction of a celestial object caused by the bending of light while passing through the Earth's atmosphere. Since the density of the atmosphere decreases with altitude, the starlight will bend more as it continues down through the atmosphere. As a result, a star will appear higher in the sky than its true direction.

atmospheric; → refraction.

atmospheric scattering
  پراکنش ِ جوی   
parâkaneš-e javvi

Fr.: diffusion atmosphérique   

The → scattering of → electromagnetic radiation by various particles in the Earth's → atmosphere. The phenomenon is caused by collisions between photons and several scattering agents such as atoms, molecules, → aerosols, and water droplets in clouds. → Rayleigh scattering.

atmospheric; → scattering.

atmospheric turbulence
  آشوبناکی ِ جوی   
âšubnâki-ye javvi

Fr.: turbulence atmosphérique   

Random fluctuations of the atmosphere caused by the constant injection of energy into the atmosphere from solar and local sources, changing the temperature and pressure of the air where it is absorbed and leading to fluid instabilities. The development over time of the instabilities gives rise to fluctuations in the density of air, and therefore the → refractive index of the atmosphere. → turbulence; → seeing.

atmospheric; → turbulence.

atmospheric windows
  روزنه‌های ِ جوی   
rowzanehâ-ye javvi (#)

Fr.: fenêtres atmosphériques   

Gaps in → atmospheric absorption, allowing a range of electromagnetic wavelengths to pass through the atmosphere and reach the Earth.

atmospheric; → window.

atoll
  آتول   
âtol (#)

Fr.: atoll   

A coral island or group of coral islands forming a ring that is surrounded by deep ocean water and that encloses a shallow lagoon. Atolls range in diameter from about 1 km to over 100 km and are especially common in the western and central Pacific Ocean. They are believed to form along the fringes of underwater volcanoes. → atoll source.

From atollon, atolon, from Divehi (Indo-Aryan language of the Maldive Islands) atolu "reef."

atoll source
  خن ِ آتول   
xan-e âtol

Fr.: source atoll   

A member of a class of → low-mass X-ray binary systems containing low-magnetic field → neutron stars. They have soft spectra and no pulsations. An example is 4U 1705-44. See also → Z source.

atoll; the name derives from the fact that on X-ray → color-color diagrams these sources often resemble a band of points at constant hard X-ray color, with "islands" of points appearing on time-scales of weeks and months.

atom
  اتم   
atom (#)

Fr.: atome   

The smallest stable unit forming the basic elements. An atom consists of positively charged → protons and → neutrons in the nucleus surrounded by negatively charged → electrons.

From L. atomus, from Gk. atomos "uncut," from → a- "not" + tomos "a cutting," from temnein "to cut."

atomic
  اتمی   
atomi (#)

Fr.: atomique   

Of or relating to an atom or atoms; of or employing nuclear energy.

Atomic, adj. from → atom + suffix → -ic

atomic clock
  ساعت ِ اتمی   
sâat-e atomi

Fr.: horloge atomique   

A modern clock, in which the characteristic frequencies of certain atoms (most commonly chosen cesium 133) are utilized for precision time measurement. → atomic fountain clock.

atomic; → clock.

atomic diffusion
  پخش ِ اتمی   
paxš-e atomi

Fr.: diffusion atomique   

element diffusion.

atomic; → diffusion.

atomic fountain
  فواره‌ی ِ اتمی   
favvâre-ye atomi

Fr.: fontaine atomique   

A gaseous ball of atoms, usually → cesium (133Cs), created by the → laser cooling technique and used in an → atomic fountain clock. The ball, typically a few millimeters in diameter and containing some 107 atoms, can be launched upward against gravity using a → laser beam. The launch velocity is chosen such that the atoms reach a height of about one meter before they turn back and fall down the same path they came up. The motion of the ball resembles that of the water in a pulsed fountain.

atomic; fountain, from M.E. fontayne from O.Fr. fontaine, from L.L. fontana, noun use of feminine of L. fontanus "of a spring," from fons "spring of water."

Favvâré, Pers. construction from Ar. faur "boiling, bubbling."

atomic fountain clock
  ساعت ِ فواره‌ی ِ اتمی   
sâ'at-e favvâre-ye atomi

Fr.: horloge à fontaine atomique   

An → atomic clock based on the principle of the → atomic fountain. A ball of atoms, usually → cesium (133Cs), created by the → laser cooling technique, is trapped in the intersection region of six laser beams. The ball is thrown upward by a laser beam and passes twice through a cavity where the atoms interact with the → microwave radiation generated by an → oscillator. The ball reaches the summit of its trajectory (about 1 m above the cooling zone) and then due to gravity falls through the same microwave cavity. The microwave radiation causes the electrons of the cesium atoms to move between two specific → energy states as they pass through the cavity. The clock is based on a → hyperfine transition (9.192631770 GHz) between two energy states in the electronic → ground state of the atom. The upper hyperfine state can in principle radiate to the lower state by → spontaneous emission, but the process takes a very long time -- thousands of years. Selection and detection of the hyperfine state is performed via → optical pumping and laser induced resonance fluorescence. In a carefully controlled setup, a relative uncertainty of 10 -16 can be reached for the cesium clock. This means an accuracy of 1 sec every 300 million years. This fluorescence is measured by a detector. The entire process is repeated until the maximum fluorescence of the cesium atoms is determined. This determination is used to lock the oscillator to the atomic frequency of cesium, which is used to define the SI → second. The first atomic fountain for metrological use was developed at the Paris Observatory (A. Clairon et al. 1996, Proc. 5th Symp. Frequency Standards and Metrology, p. 45).

atomic fountain; → clock.

atomic heat
  گرمای ِ اتمی   
garmâ-ye atomi

Fr.: chaleur atomique   

The → heat capacity of a → mole of a substance, expresses as: Ca = C.A , where C is the → specific heat and A the → atomic weight .

atomic; → heat.

atomic hydrogen
  هیدروژن ِ اتمی   
hidrožen-e atomi (#)

Fr.: hydrogène atomique   

Same as → neutral hydrogen or → H I.

atomic; → hydrogen.

atomic mass
  جرم ِ اتمی   
jerm-e atomi (#)

Fr.: masse atomique   

The mass of a single atom, when the atom is at rest at its lowest energy level (→ ground state). Because a → chemical element may exist as various → isotopes, possessing different numbers of neutrons in their atomic nuclei, atomic mass is calculated for each isotope separately. Atomic mass is most often expressed in unified → atomic mass units, where one unified atomic mass unit is defined as one-twelfth the mass of a single atom of the carbon-12 isotope.

atomic; → mass.

<< < -es -iv -ti 21 a p abe abs abs aca acc acc acr act ada adh Adr aer aga air Alf Alg alk Alp alt alu amm ana And ang ani ano ant ant Ap apo app app Aqu Arc arg arr asc ass ast ast asy atm ato att aur aut axi B-m bad Bal bar bar Bay Bed ber Bet bif bim bin bio bis bla ble blu Bod Bol bor bou Bra Bre bro bul C-t Cal Cam can car Car Cas cat cav cel cen cer Cha cha Cha che chl Cir cir cir Cla cli clo clu co- coc coh col col col Com com com com com com com com Com con con con con con con con con con con con con coo Cor Cor cor cos cos cos Cou cou Cra Cre cri cro cub cur cyc cyl Dan dat Dav de- Deb dec dec dee def deg del Den den der det deu dew dic dif dif dil Dip dir dis dis dis dis dis diu dod Dop dou Dra dua dus dwa dyn DZ Ear ecc eco edi EHB Ein ela ele ele ele ele ell eme emp end Eng ent epi equ equ era ESP eth Eur evi exa exc exe exi exp exp ext ext ext fac fal far fec Fer fer fie fin fir fis fla Flo flu fog for for Fou fra fre fre Fro fun G s Gal gal gal Gar gau geg gen geo geo geo ger gla gly gra gra gra gra gra Gre gro GYR Had Hal hap Har HD hea hel hel Hen Her hex hig Hil hol Hoo hor hou Hub hum hyb hyd hyd hyp hys ide ign ima imp imp in- inc Ind ind ine inf inf inf ini ins ins ins int int int int Int int int int inv ion iri irr iso iso iso Jea Jor jum K c Kep Ker kin kno lab Lam Lan Lap las lat Le lef len lev lig lig lin lin lin liq Lit loc log lon lou LS lun lun Lym M s Mag mag mag mag mag mag maj man Mar mas mas mat May mea mec mel mer mes met met met mic mid mil Min Mir mix mod mod mol mon mor mov mul mur mys nan nat nav nec Nep neu New New NGC nob nom non non nor nos nuc nuc num nut obj obl obs occ oct off oli oni ope opp opt opt orb ord org orp osc out ove oxi P-w pal par par par par Pas pat pej per per per per per per pha Phe pho pho pho phy pin pla Pla pla pla pla plu poi pol pol Pol pol por pos pot Poy pre pre pre pre pri pri pri pro pro pro pro pro pro Psa pul pum Q i qua qua qua qua R A rad rad rad rad rad rad Ram Ran rat rea rea rec rec red red ref ref reg rei rel rel rem rep res res res ret rev Rho Rie ril riv rog Ros rot rul S A Sag sam sat sca sca Sch Sco Sec sec sec seg sel sem sen set Sha sha shi sho sid sig sim sin Sir ske sli Smo soc sof sol sol sol sol sou sou spa spe spe Spe spe sph spi Spi spr sta sta sta sta sta ste ste ste Sto str str sub sub sub suc sun sup sup sup sup sur swa syn syn tac tas tel tem ter tes the the the the thi thr tid til tip ton tor tou tra tra tra tra Tri tri tru tsu tur two Typ UHE ult unc uni uni uni upg ura uti val var vec Vel ver Ver vie Vir vis vis vol W-R war wav wav wea Wei wha wid win WN3 Wol wri xen yok zen zij > >>