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: 466 Search : pH
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.

automatic photometric telescope
  دوربین ِ شیدسنجیک ِ خودکار، تلسکوپ ِ ~ ~   
durbin-e šidsanjik-e xodkâr, teleskop-e ~ ~

Fr.: télescope photométrique automatique   

A telescope developed to perform photometric observations automatically.

automatic; → photometric; → telescope.

automorphism
  خود-ریخت‌مندی   
xod-rixtmandi

Fr.: automorphisme   

An → isomorphism between an → object and itself.

auto-; → morphism.

Baldwin-Phillips-Terlevich diagram
  نمودار ِ بالدوین-فیلیپس-ترلویچ   
nemudâr-e Baldwin-Phillips-Terlevich

Fr.: diagram de Baldwin-Phillips-Terlevich   

A set of nebular → emission line diagrams used to distinguish the ionization mechanism of → nebular gas. The most famous version consists of [N II]λ6584/Hα versus [OIII] λ5007/Hβ. The next two more commonly used BPT diagnostics are [S II] λλ6717,6731/Hα versus [O III] λ5007/Hβ and [O I] λ6300/Hα versus [O III]λ5007/Hβ. These diagrams use strong, optical lines of close proximity in the ratios to limit → reddening and → spectrophotometric effects. They are able to clearly distinguish different classes of → ionization, for example → LINERs from normal → H II regions and → active galactic nuclei.

Baldwin, J. A., Phillips, M. M., Terlevich, R., 1981 PASP 93, 5; → diagram.

baryon-photon ratio
  وابر ِ باریون-فوتون   
vâbar-e bâriyon-foton

Fr.: rapport baryon-photon   

The → baryon number compared with the number of photons in the → Universe. The baryon-photon ratio can be estimated in a simple way. The → energy density associated with → blackbody radiation of → temperature  T is aT4, and the mean energy per photon is ~kT. Therefore, the number density of blackbody photons for T = 2.7 K is: nγ = aT4/kT = 3.7 x 102 photons cm-3, where a = 7.6 x 10-15 erg cm-3 K-4 (→ radiation density constant) and k = 1.38 x 10-16 erg K-1 (→ Boltzmann's constant). The number density of baryons can be expressed by ρm/mp, where ρm is the mass density of the Universe and mp is the mass of the → proton (1.66 x 10-24 g). → CMB measurements show that the baryonic mean density is ρm = 4.2 x 10-31 g cm-3 (roughly 5% of the → critical density). This leads to the value of ~ 2 x 10-7 for the number density of baryons. Thus, the baryon/photon ratio is approximately equal to η = nb/nγ = 2 x 10-7/3.7 x 102 ~ 5 x 10-10. In other words, for each baryon in the Universe there is 1010 photons. This estimate is in agreement with the precise value of the baryon-photon ratio 6.14 x 10-10 derived with the → WMAP. Since the photon number and the baryon number are conserved, the baryon-photon ratio stays constant as the Universe expands.

baryon; → photon; → ratio.

Be phenomenon
  پدیده‌ی ِ Be   
padide-ye Be

Fr.: phénomène Be   

The episodic occurrence of abrupt → mass loss in → Be stars resulting in → Balmer lines in emission and → infrared excess. The Be phenomenon results from a combination of a long-term secular effect and short-term instabilities, such as pulsation. The secular evolution brings the star close enough to the critical → break-up velocity, so that the additional velocity field due to the instability may allow some mass ejection (Maeder 2011).

Be star; → phenomenon.

beat Cepheid
  کِفِیءوسی ِ زنشی   
kefeusi-ye zaneši

Fr.: céphéide à battement   

A Cepheid variable in which two or more almost identical periods of variability pass into and out of phase with each other, producing periodic amplitude fluctuations in their light curves. Beat periods are typically about 2 hours.

beat; → Cepheid.

Beta Cephei
  بتا-کفؤس   
betâ-Kefeus

Fr.: bêta Céphée   

The second brightest star in the constellation → Cepheus and the prototype of → Beta Cephei variables. It is a variable B2 type → giant star with a visual magnitude of 3.23 varying with a period of 4.57 hours. Its mass is a dozen times that of the Sun. Beta Cephei is a → triple system lying at a distance of about 600 → light-years. The inner → spectroscopic companion, → spectral type A, is only about 45 AU away, and takes around 90 years to orbit. The third visual companion is at least 2400 AU away, with an orbital period of at least 30,000 years.

Beta (β), the second letter of the Gk. alphabet; → Cepheus.

Beta Cephei variable
  ورتنده‌ی ِ بتا-کفؤسی   
vartande-ye betâ Kefeusi

Fr.: variables bêta Céphée   

A variable star, of early B or late O types, undergoing radial pulsations with short periods (< 1 day). Beta Cephei stars are confined within a narrow band of the → H-R diagram above the upper → main sequence. They are believed to be near the end of core hydrogen-burning stars of approximately 10 to 20 solar masses. The famous bright stars → Spica and → Mirzam belong to this family.

Beta Cephei; → variable.

bijective morphism
  ریخت‌شناسی ِ دوشانی   
rixtšenâsi-ye došâni

Fr.: morphisme bijectif   

Same as → isomorphism.

bijective; → morphism.

biophysicist
  زیست‌فیزیکدان   
zistfizikdân (#)

Fr.: biophysicien   

A specialist in → biophysics.

bio-; → physicist.

biophysics
  زیست‌فیزیک   
zistfizik (#)

Fr.: biophysique   

The science that deals with biological structures and processes involving the application of physical principles and methods.

Biophysics, from → bio- + → physics.

Zistfizik, from zist-, → bio- + fizikphysics.

biosphere
  زیست‌سپهر   
zistsepehr (#)

Fr.: biosphère   

The part of a planet or moon within which life can occur. It may include the crust, oceans, and atmosphere.

Biosphere, from → bio- + → sphere.

Zistsepehr, from zizt-, → bio-, + sepehrsphere.

blackbody photosphere
  شیدسپهر ِ سیه‌جسم   
šidsepehr-e siyah-jesm

Fr.: photosphère de corps noir   

The → blackbody surface of the → Universe defined at a → redshift of about z ≥ 2 × 106. This is distinct from the → last scattering surface, in other words the → cosmic microwave background radiation (CMBR), which refers to z = 1100. Prior to the epoch of the blackbody photosphere the distortions from the → Big Bang are exponentially suppressed.

blackbody; → atmosphere.

Bonnor-Ebert sphere
  سپهر ِ بونور-ابرت، کره‌ی ِ ~   
epehr-e Bonnor-Ebert, kore-ye ~

Fr.: sphère de Bonnor-Ebert   

A sphere of interstellar gas at uniform temperature in equilibrium under its own gravitation and an external pressure. The pressure of a hotter surrounding medium causes the sphere to collapse. → Bonnor-Ebert mass.

Bonnor-Ebert mass; → sphere.

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