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: 95 Search : hot
aperture photometry
  شیدسنجی ِ دهانه‌ای   
šidsanji-ye dahânéi

Fr.: photométrie d'ouverture   

Photometry using a diaphragm to isolate a small sky area, either directly with a focal-plane diaphragm, or with an image processing system.

aperture; → photometry.

astrophotography
  اختر‌شیدنگاری، شیدنگاری ِ اختری   
axtar-šidnegâri, šidnegâri-ye axtari

Fr.: astrophotographie   

The photography of stars, other celestial bodies, and stellar fields.

astro-, → photography.

astrophotometry
  اخترشیدسنجی، شیدسنجی ِ اختری   
axtar-šidsanji, šidsanji-ye axtari

Fr.: astrophotométrie   

The measurement of the intensity of light of celestial bodies.

Astrophotometry, from → astro- + → photometry.

Axtar-šidsanji, from axtar-, → astro-, + -šidsanji, → photometry.

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.

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.

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.

broad-band photometry
  شیدسنجی ِ پهن-باند   
šidsanji-ye pahn-bând

Fr.: photométrie à bande large   

Photometric measurements carried out through filters with a band-width (about one-tenth the central wavelength) in the range 30-100 nm. Typical examples are Johnson photometry, Krons-Cousins RI photometry, and the six-color system.

broad; → band; → photometry.

dichotomy
  دوپارگی   
dopâregi

Fr.: dichotomie   

1) General: A division in two parts or kinds that differ widely from or contradict each other.
2) Astro.: The phase of the Moon or a planet when half of its surface appears illuminated by the Sun.

From Gk. dichotomia "cutting in two," from dicho- "apart, in two," combining form of dicha "in two, asunder," akin to → di-, + temnein "to cut."

Dopâregi, from dotwo + pâré "piece, part, portion, fragment" (Mid.Pers. pârag "piece, part, portion; gift, offering, bribe;" Av. pāra- "debt," from par- "to remunerate, equalize; to condemn;" PIE *per- "to sell, hand over, distribute; to assign;" cf. L. pars "part, piece, side, share," portio "share, portion;" Gk. peprotai "it has been granted;" Skt. purti- "reward;" Hitt. pars-, parsiya- "to break, crumble") + -(g)i a noun/state suffix.

external photoelectric effect
  اسکر ِ شید-برقی ِ برونی   
oskar-e šid-barqi-ye boruni

Fr.: effet photoélectrique externe   

The → photoelectric effect in solids where free electrons are emitted from the surface of a substance (e.g., → semiconductor) when radiation of appropriate frequency falls on it. Also called → photoemissive effect.

external; → photoelectric; → effect.

extrinsic photoconductivity
  شیدهازندگی ِ برونگین   
šidhâzandegi-ye borungin

Fr.: photoconductivité extrinsèque   

Photoconductivity due to the addition of impurities or external causes.

extrinsic; → photoconductivity.

Šidhâzandegi, → photoconductivity; borungin, → extrinsic.

gravitational slingshot
  فلاخن ِ گرانشی   
falâxan-e gerâneši

Fr.: fronde gravitationnelle   

Same as → gravity assist.

gravitational; slingshot, from sling, from M.E. slyngen, from O.N. slyngva "to sling, fling" + shot, from M.E., from O.E. sc(e)ot, (ge)sceot; cf. Ger. Schoss, Geschoss.

Falâxan "sling;" from Av. fradaxšana- "sling," fradaxšanya- "sling, sling-stone;" → gravitational.

hot
  داغ   
dâq (#)

Fr.: chaud   

Having a relatively high temperature. → hot accretion flow, → hot core, → hot corino, → hot dark matter , → hot dust-obscured galaxy, → hot Jupiter, → hot molecular core, → hot pixel, → hot star.

Hot, O.E. hat, "hot; fervent, fierce," from P.Gmc. *haitoz (cf. Du. heet, Ger. heiß "hot," Goth. heito "heat of a fever").

Dâq "hot; brand, marking," from Mid.Pers. dâq, dâk "hot," dažitan "to burn, scorch," dažišn "burning" (Mod.Pers. dežan (دژن) "acid, pugnent"), from Av. dag-, daž- "to burn;" cf. Skt. dah- "to burn;" L. fovere "to warm, heat; " Arm. dažan "violent, wild;" Lith. degu "to burn;" O.E. fefor; E. fever. PIE base *dhegh- "to burn."

hot accretion flow
  تچان ِ فربال ِ داغ   
tacân-e farbâl-e dâq

Fr.: écoulement d'accrétion chaud   

A type of → accretion flow by a → compact object such as a → black hole which has a high → virial temperature, is → optically thick, and occurs at lower mass → accretion rates compared with → cold accretion flows. In a hot accretion flow with a very low mass accretion rate, the electron mean free path is very large, and so the accreting → plasma is nearly collisionless. In this type of accretion flow, thermal conduction transports the energy from the inner to the outer regions. As the gas temperature in the outer regions can be increased above the → virial temperature , the gas in the outer regions can escape from the gravitational potential of the central black hole and form outflows, significantly decreasing the mass accretion rate.

cold; → accretion; → flow.

hot core
  مغزه‌ی ِ داغ   
maqze-ye dâq

Fr.: cœur chaud   

Same as → hot molecular core.

hot; → core.

hot corino
  مغزک ِ داغ   
maqzak-e dâq

Fr.: petit cœur chaud   

A warm, compact → molecular clump found in the inner envelope of a → Class 0 → protostar. Hot corinos are low-mass analogs of → hot molecular cores (HMCs) occurring in → massive star formation sites. With a typical size of ≤ 150 → astronomical units, hot corinos are two orders of magnitude smaller than HMCs. They have densities ≥ 107 cm-3 and temperatures ≥ 100 K (Ceccarelli, C. 2004, ASP Conf. Ser. 323, 195).

hot; corino, from → core + -ino a diminutive suffix in It.

hot dark matter
  مادّه‌ی ِ تاریک ِ داغ   
mâdde-ye târik-e dâq (#)

Fr.: matière noire chaude   

Any form of → dark matter which had a significant velocity dispersion (comparable to the velocity of light), when the Universe first became → matter-dominated.

hot; → dark; → matter.

hot dust-obscured galaxy (HDOG)
  کهکشان ِ تیره با غبار ِ داغ   
kahkešân-e tiré bâ qobâr-e dâq

Fr.: galaxie obscure à poussière chaude   

A member of the most extreme galaxies in terms of their luminosities and unusual hot → dust temperatures. The → infrared emission from HDOGs is dominated by obscured accretion onto a central → supermassive black hole (SMBH), in most cases without significant contribution from → star formation. The large contrast between the underlying → host galaxy and the hyper-luminous emission from the → active galactic nucleus (AGN) implies that either the SMBH is much more massive than expected for the stellar mass of its host, or is radiating well above its → Eddington limit. The most extreme of these remarkable systems known is → W2246-0526.

hot; → dust; → obscure; → galaxy.

hot electron diode
  دیود ِ الکترون ِ داغ   
diod-e elektron-e dâq

Fr.:diode à électrons chauds   

Same as → Schottky diode

hot; → electron; → diode.

hot Jupiter
  هرمز ِ داغ   
Hormoz-e dâq

Fr.: Jupiter chaud   

A giant, gaseous, Jupiter-like planet lying too close to its parent star and having an orbital period from a few days to a few weeks. The existence of hot Jupiters is usually interpreted in terms of planetary migration. These planets can, in principle, be formed at larger distances from their stars and migrate to the inner regions due to dynamical interaction with the proto-planetary disk.

hot; → Jupiter.

hot molecular core (HMC)
  مغزه‌ی ِ مولکولی ِ داغ   
maqze-ye molekuli-ye dâq

Fr.: cœur moléculaire chaud   

A relatively small, dense, and hot → molecular clump occurring in regions of → massive star formation. HMCs have diameters ≤ 0.1 pc, densities ≥ 107 cm-3, and temperatures ≥ 100 K. The densest hot cores are traced in → ammonia (NH3) and possess densities of 108 cm-3, sizes down to 0.05 pc and temperatures of up to 250 K. Hot molecular cores are generally associated with → compact H II regions and → ultracompact H II regions. High angular resolution observations suggest that HMCs are internally heated by embedded sources, since temperature and density increases toward the center as expected if star formation is occurring close to the core center. Same as → hot core.

hot; → molecular; → core.

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