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: 13046 Search : far
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.

atomic mass number (A-number)
  عدد ِ جرم ِ اتمی   
adad-e jerm-e atomi (#)

Fr.: nombre de masse atomique   

The total number of → protons and → neutrons in the → nucleus of an → atom (symbol A). For example, Oxygen-16 has a mass number of sixteen, because it has eight protons and eight neutrons.

atomic; → mass; → number.

atomic mass unit (amu)
  یکای ِ جرم ِ اتمی   
yekâ-ye jerm-e atomi (#)

Fr.: unité de masse atomique   

A unit of mass used for atoms and molecules, equal to 1/12 of the mass of an atom of carbon-12 (including orbital electrons). It is equal to 1.660 33 × 10-24 g.

atomic; → mass; → unit.

atomic nucleus
  هسته‌ی ِ اتم   
haste-ye atom (#)

Fr.: noyau atomique   

The central part of the → atom. It is made up of → protons and, in most cases, → neutrons. The nucleus is surrounded by a swarm of fast-moving → electrons. Almost all of the mass (more than 99%) of an atom is contained in the dense nucleus. The number of protons in the nucleus (called → atomic number) determines the type of → chemical element. Atoms that differ only in the number of neutrons in their nuclei are called → isotopes.

atomic; → nucleus.

atomic number
  عدد ِ اتمی   
adad-e atomi (#)

Fr.: nombre atomique   

The number of → protons in an → atomic nucleus (symbol Z). Same as → Z-number. The atomic number is written as a subscript to the left of the → chemical element name. For example, the most common isotope of oxygen is shown as 816O, which has 8 → protons and its → mass number (A) is 16.

atomic; → number.

atomic proposition
  گزاره‌ی ِ اتمی   
gozâre-ye atomi

Fr.: proposition atomique   

In → propositional logic, a → sentence without any → connectives. See also → molecular proposition.

atomic; → proposition.

atomic time
  زمان ِ اتمی   
zamân-e atomi (#)

Fr.: temps atomique   

Time measured using atomic clocks.

atomic; → number.

<< < -es -iv -ti 21 a p abe abs abs aca acc acc acr act ada adh Adr aer AGB air Alf Alg all alp alt AM amo ana And ang ani ano Ant Ant apa apo app app Ara arc Ari arr Asi ass ast ast asy atm ato att aut ave axi Bab bal ban bar bar bea Bel Bes bia Big bin bin bip Bla bla bli blu Boh Bon bos Bou bra bri bro bur cal cal can Cap car Car cat Cau cea Cen cen cha Cha cha che chi chr cir cir civ cla clo clo CMB coa coe coh col col col com com com com com com com com com con con con con con con con con con con con coo cop Cor CoR cor cos cos Cou cou CP- cre cri cro cub cur cya Cyg dan dar dau de- deb dec dec dee def deg del den den dep des deu dew dia dif dif dih dip dir dis dis dis dis dis diu doc dop dou DQ dry dus dwa dyn Dys 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 eye fac fal Far fed Fer fer fie fin fir fit fla flo flu fol for for Fou fra fre Fre fro fuz gai Gal Gal gam gas Gau gen gen geo geo geo gia glo gol gra gra gra gra gre gri gui H I hai Ham har Hau hea hec hel hel her HES hie hig his hom hor hot Hub Hul Huy hyd hyd hyl hyp ice ide ima imm imp imp inc ind ind ine inf inf inf inh inn ins ins int int int int int int int int inv ion ion Irr iso iso iso Jal JHK Jul jur Kel Kep kin kne L d Lag lam Lap lar lat law Lea len lep lib lig lin lin lin liq lit loc log lon Los low lum lun Lut Lyr mac mag mag mag mag mag maj man Mar mas mas mat Max mea mec mel Mer Mes met met met mic mid Mil min mir mix mod mod mol mon mor mov mul muo mys nan nat Nav nec nep neu new New NGC Noa nom non non nor not nuc nuc num nyc obj obs obs oce odd OH Omi Oor ope opt opt opt orb ord Ori ort osc out ove oxi pai pan par Par Par par pas pea Pen per per per per Per per pha phl pho pho pho phy Pip Pla pla PLA pla ple plu pol pol pol pol pop pos pos pot Pra pre pre pre pre pri pri pro pro pro pro pro pro pro pse pul pur qua qua qua qua qui rad rad rad rad rad rad raf ran rar ray rea rea rec rec red red ref ref reg rel rel rel rep res res res res ret rev ric rig rin roc ROS rot Rox rus Sad sal sat sca sca Sch sci scy sec sec see sel sem sen Ser sex Sha she sho sid sig sil sim sin siz sle SMA SNR Sof sol sol sol sol sou Sou spa Sp spe spe spe sph spi Spi spr sta sta sta sta sta ste ste ste sto str str Sty sub sub suc sun sup sup sup sup sur Swa syn syn tac tas tel tem ter tes the the the the Tho thr tid tim Tit top tot tra tra TRA tra tre tri tri tru tum tur TY Typ ult una und uni uni uno upp urg UX Van var veg vel ver vib vio vir vis Voi vow wan wat wav WC wea wel whi Wil wir WNh wor X-r yel ytt zer zon > >>