An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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tumbling motion
  جنبش ِ کلتاوی   
jonbeš-e kaltâvi

Fr.:   

The motion of a solid body whose rotation axis is not fixed in space. For example, that of an asteroid that does not rotate about one of their principal axes. → tumbling asteroid.

tumble; → motion.

TW Hydrae association
  آهزش ِ TW هودرا   
âhazeš-e TW Hudrâ

Fr.: Association TW Hydrae   

A young (≤ 100 million years) association of stars (abbreviated TWA) with at least 27 members, from → intermediate mass stars to planetary mass objects. Five of them, including → TW Hydrae, display signatures of → T Tauri stars. TWA is the first moving group of young nearby (≤ 100 → paesecs) stars to be identified.

TW Hydrae; → association.

Two Micron All Sky Survey (2MASS)
     
2 MASS

Fr.: 2MASS   

An astronomical → survey conducted from 1997 to 2001 of the entire sky in near-infrared J, H, and K bands (wavelengths 1.25, 1.65, and 2.17 microns respectively). The aim was to detect and characterize point sources brighter than about 1 → mJy in each band, with → signal-to-noise ratio greater than 10, using a pixel size of 2".0. Two automated 1.3-m telescopes were used, one at Mt. Hopkins, AZ, and one at CTIO, Chile. 2MASS is currently producing the following data products: 1) A digital atlas of the sky comprising approximately 4 million 8' × 16' images, having about 4" spatial resolution in each of the wavelength bands. 2) A point source catalog containing accurate positions and fluxes for 300 million stars and other unresolved objects. 3) An extended source catalog containing positions and total magnitudes for more than 1,000,000 galaxies and nebulae.

two; → micron; → all-sky survey.

two-dimensional flow
  تچان ِ دو-وامونی   
tacân-e do-vâmuni

Fr.: écoulement bi-dimensionnel   

A flow whose parameters are functions of time and two space coordinates (x and y) only. There is no variation in the z direction and therefore the same → streamline pattern could at any instant be found in all planes in the fluid perpendicular to the z direction (B. Massey, Mechanics of Fluids, Taylor & Francis, 2006).

two; → dimensional; → flow.

two-photon emission
  گسیل ِ دو-فوتونی   
gosil-e do-fotoni

Fr.: émission à deux photons   

The simultaneous emission of two photons whose sum of energies is equal to that of a single electron transition. The energy of each individual photon of the pair is not fixed, so that the spectrum of two-photon emission is continuous from the wavelength of that transition to infinity. In practice, there is a peak in wavelength distribution of the emitted photons. Two-photon emission is studied atomic physics with application in astrophysics, as it contributes to the continuum radiation from → planetary nebulae. It was recently observed in condensed matter and specifically in → semiconductors.

two; → photon; → emission.

Tychonic model
  مدل ِ توگویی   
model-e Tychoyi

Fr.: modèle tychonique   

A hybrid of → geocentric and → heliocentric systems in which the Earth remains at the center, with the → Sun orbiting the Earth, but with all the other planets revolving about the Sun. Moreover, the fixed stars were located in a crystalline shell centered on the Earth.

Related to the Danish astronomer Tycho Brahe (1546-1601), who imagined the model; → model.

Type I migration
  کوچ ِ گونه‌ی ِ I   
kuc-e gune-ye I

Fr.: migration de type I   

An → orbital migration of low-mass → planets in which no gap is created in the → protoplanetary disk. According to planetary models, beyond a critical core mass for the forming planet, a gap in the protoplanetary disk is created. The critical mass depends on the mass and → metallicity of the disk and therefore it does not have a singular value, but has been shown to be between about 10-30 Earth masses. Compare with → Type II migration.

type; → migration.

Type II migration
  کوچ ِ گونه‌ی ِ II   
kuc-e gune-ye II

Fr.: migration de type II   

The → orbital migration of forming → planets that → accrete enough disk material to exceed the critical mass. This type migrates in a gap created in the → protoplanetary disk. Compare with → Type I migration.

type; → migration.

ultracompact H II region
  ناحیه‌ی ِ H IIی ِ اولتر-همپک   
nâhiye-ye H II-ye ultar hampak

Fr.: région H II ultracompacte   

A very young → H II region fully embedded in its natal molecular cloud. Ultracompact H II regions are distinguished from classical H II regions by their small sizes (diameter ≥ 0.1 pc), high densities (Ne ≥ 105 cm-3), and high emission measures (EM ≥ 107 pc cm-6). Their typical ionized gas content is about 10-2  → solar masses, in contrast to classical H II regions with a mass of about 105 solar masses. Due to very important extinction, ultracompact H II regions are not accessible to visible wavelengths.

ultra-; → compact; → H II region.

ultrasonics
  اولتر-صداییک، اولتر-سداییک   
ultar-sedâyik

Fr.: physique des ultra-sons   

The branch of physics dealing with elastic waves of frequencies above 20 kHz to 1010 kHz propagated in solids, liquids, and gases.

ultra-; sonic from L. sonussound + → -ics.

ultraviolet astronomy
  اخترشناسی ِ فرابنفش، ~ اولتر-بنفش   
axtaršenâsi-ye farâ-banafš, ~ ultar-banafš

Fr.: astronomie ultraviolette   

The study of astronomical objects in the ultraviolet portions of the electromagnetic spectrum, in the waveband 3000 Å to about 10 Å. At these wavelengths, the atmosphere prevents ultraviolet radiation from reaching the Earth surface. Therefore ground-based observatories cannot observe in the ultraviolet. Only with the advent of space-based telescopes has this area of astronomy become available for research.

ultraviolet; → astronomy.

unbounded function
  کریای ِ بیکران   
karyâ-ye bikarân

Fr.: fonction non bornée   

The function y = f(x) in a given range of the argument x if there is no number M such that for all values of x in the range under consideration the inequality | f(x) | ≤ M will be fulfilled. → bounded function.

unbound; → function.

unconditional
  نابوتاری، نابوتارمند   
nâbutâri, nâbutârmand

Fr.: inconditionnel   

Not limited by conditions; absolute.

un-; → conditional.

unconscious
  ناهاسن   
nâhâsan

Fr.: non conscient   

Not awake and aware; not responding to one's environment.

non-; → conscious.

unconsciousness
  ناهاسنی   
nâhâsani

Fr.: non conscience   

The → state of being → unconscious.

unconscious; → -ness.

undulation
  موجش   
mowješ

Fr.: ondulation   

A wave; the motion of waves.
A wavelike motion in any medium.

From L.L. undulatus "wavy, undulated," from undula "wavelet," diminutive of L. unda "wave."

Mowješ, verbal noun of mowjidan "to undulate," from mowjwave.

unification
  یگانش   
yegâneš

Fr.: unification   

1) The process of unifying or uniting; union.
2) The state or condition of being unified (Dictionary.com).

Verbal noun of → unify.

uniform circular motion
  جنبش ِ دایره‌ای ِ یکدیس، ~ ~ یکنواخت   
jonbeš-e dâyereyi-ye yekdis, ~ ~ yeknavâxt

Fr.: mouvement circulaire uniforme   

The motion of an object around a fixed point at a constant angular speed, and at constant radius.

uniform; → circular; → motion.

uniform motion
  جنبش ِ یکدیس، ~ ِ یکنواخت   
jonbeš-e yekdis, ~ yeknavâxt

Fr.: mouvement uniforme   

Motion at a constant → velocity. The state of rest is a special case of uniform motion. → accelerated motion; → inertial motion.

uniform; motion.

union
  یکایش   
yekâyeš

Fr.: union   

General: The act of uniting two or more things.
A number of persons, organizations, states, etc., joined or associated together for some common purpose, e.g. → International Astronomical Union (IAU).
Math.: A set containing all the elements of two or more sets being combined. It is represented by ∪.

M.E. from O.Fr. union from L.L. unionem (nominative unio) "oneness, unity," from unus, → one, cognate with Pers. yek, as below.

Yekâyeš, from yek, → one, + -ây- epenthetic vowel, + -eš verbal noun suffix, → -tion.

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