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

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 1010
presolar grain
  دانه‌ی ِ پیش-خورشیدی   
dâne-ye piš-xoršidi

Fr.: grain pré-solaire   

A → refractory → nanoparticle embedded in → meteorites and → interplanetary dust particles whose → isotopic ratios suggest formation earlier than the Solar System.

presolar; → grain.

Press-Schechter formalism
  دیسه‌گرایی ِ پرس-ششتر   
disegerâyi-ye Press-Schechter

Fr.: formalisme de Press-Schechter   

A mathematical analysis, based on → self-similarity, used to predict the → mass function of spherically collapsing → dark matter halos. The formalism assumes that the fraction of mass in halos more massive than M is related to the fraction of the volume in which the smoothed initial density field is above some threshold δcρ, where ρ is the average density of the Universe, with the volume encompassing a mass larger than M. A variety of smoothing → window functions and thresholds have been argued, but the most common is a top-hat window in real space and δc≅ 1.69. The Press-Schechter formalism provides a relatively good fit to the results of numerical simulations in cold dark matter theories.

First described by William H. Press and Paul Schechter's paper (1974, ApJ 187, 425); → formalism.

pressure
  فشار   
fešâr (#)

Fr.: pression   

The force per unit area.

M.E., from O.Fr. pressure, from L. pressura "action of pressing," from pressus, p.p. of premere "to press, compress."

Fešâr "squeezing, constriction, compression," verb fešordan, fešârdan "to press, squeeze;" phonetic variants Lori xošâr, Aftari xešâr, Qazvini, Qomi xošâl; cf. Khotanese ssarr- "to exhilarate;" loaned in Arm. ôšarak, in Ar. afšaraj "juice."

pressure broadening
  پهنش ِفشاری   
pahneš-e fešâri

Fr.: élargissement par pression   

A broadening of spectral lines caused mainly by the stellar atmospheric density and the surface gravity of the star. The line strength of a spectral line depends on the number of atoms in the star's atmosphere capable of absorbing the wavelength in question. For a given temperature, the more atoms there are, the stronger and broader the spectral line appears. Denser stars with higher surface gravity will exhibit greater pressure broadening of spectral lines.

pressure; → broadening.

pressure gradient
  زینه‌ی ِ فشار   
zine-ye fešâr

Fr.: gradient de pression   

The pressure difference between two adjacent regions of a fluid that results in a force being exerted from the high pressure region toward the low pressure region.

pressure; → gradient.

pressure gradient force
  نیروی ِ زینه‌ی ِ فشار   
niru-ye zine-ye fešâr

Fr.: force du gradient de pression   

A force resulting from → pressure gradient that is directed from high to low pressure.

pressure; → gradient; → force.

pressure ionization
  یونش ِ فشاری   
yoneš-e fešâri

Fr.: ionisation par pression   

A physical state of dense matter in which the electrostatic field of one atom should influence a neighboring atom and hence disturb atomic levels. In extreme case, such as white dwarfs, electron clouds practically rub and electrons are ionized off the parent atoms.

pressure; → ionization.

pressure scale height
  بلندی ِ مرپل ِ فشار   
bolandi-ye marpel-e fešâr

Fr.: hauteur d'échelle de pression   

A basic ingredient of the → mixing length theory that scales with the → mixing length. It is defined by the relation: HP = -dr/dln P = -Pdr/dP , where r is the height and P the pressure. See also → scale height.

pressure; → scale; → height.

previous
  پیشین   
pišin (#)

Fr.: précédent   

Occurring before something else in time or order.

From L. praevius "leading the way," from prae-, → pre- + via "way."

Pišin, from piš "before," → pre-.

previously
  پیشانه   
pišâné

Fr.: précédemment, auparavant   

Coming or occurring before something else; prior.

previous; → -ly.

Prevost's law of exchanges
  قانون ِ گهولش ِ په‌ره‌وُ   
qânun-e gahuleš-e Prévost

Fr.: loi des échanges de Prévost   

A statement concerned with thermodynamic heat exchange, according to which bodies in → thermal equilibrium are simultaneously absorbing and emitting radiant energy. A body radiates in the same way whether other bodies are present or not. Also called Prevost's theory of exchanges.

Named after Pierre Prévost (1751-1839), a Swiss philosopher and physicist, who, in 1791, put forward the statement; → law; → exchange.

Priestley's rings
  حلقه‌های ِ پریستلی   
halqehâ-ye Priestley

Fr.: anneaux de Priestley   

The concentric colored rings formed by an electrical → spark when a → discharge takes place on a metallic plate.

Joseph Priestley (1733-1804), English chemist, author, and clergyman; → ring.

primary
  نخستان   
naxostân

Fr.: primaire, principal   

1) First or highest in rank or importance; chief; principal.
2) Abbreviation for → primary body, → primary star, or → primary mirror.

M.E., from L. primarius "of the first rank, principal," from primus "first."

Naxostân, from naxost, from Mid.Pers. naxust "the first," Parthian Mid.Pers. nxwšt, from naxu, Manichean Parthian nwx "beginning" + -ist superlative suffix, Av. -išta-, cf. Skt. -istha-, Gk. -istos, O.H.G. -isto, -osto, O.E. -st, -est, -ost.

primary body
  جسم ِ نخستان   
jesm-e naxostân

Fr.: corps principal   

The body that is being orbited; such as the → Sun in the → solar system. As regards → multiple star systems, the most massive, or → primary star. See also: → secondary body.

primary; → body.

primary cell
  پیل ِ نخستان   
pil-e noxostân

Fr.:   

A → cell in which the electrochemical action producing the current is not normally reversible. Such a cell cannot be recharged by an electric current. → secondary cell.

primary; → cell.

primary cosmic rays
  پرتوهای ِ کیهانی ِ نخستان   
partowhâ-ye keyhâni-ye naxostân

Fr.: rayons cosmiques primaires   

The → cosmic rays which arrive on the Earth's → atmosphere from the outer space. The primary cosmic rays are very high energy → protons and to a lesser extent heavier nuclei which rain upon the Earth from all diretions in the outer space. They contain about 90% protons, 7% → alpha particles and about 1% still heavier nuclei of amost all the atoms from Li to Ni ( → mass number< 60). See also: → secondary cosmic rays.

primary; → cosmic; → ray.

primary eclipse
  گرفت ِ نخستان   
gereft-e noxostân

Fr.: éclipse primaire   

Of a transiting → exoplanet, the event and the interval of time during which the planet passes in front of its host star. The planet occults a portion of the stellar disk, and a fraction of light from the star is seen after traversal through the atmosphere around the planet's limb. → secondary eclipse.

primary; → eclipse.

primary mirror
  آینه‌ی ِ نخستان   
âyene-ye noxostân

Fr.: miroir primaire   

In a → reflecting telescope, the first mirror that collects the light and focuses it to the → focal plane.

primary; → mirror.

primary rainbow
  رنگین‌کمان ِ نخستان   
rangin-kamân-e naxostân

Fr.: arc-en-ciel primaire   

The main rainbow that forms between about 40° and 42° from the → antisolar point (or about 50° from the → antisolar point), as viewed by the observer. The light path involves → refraction and a → single  → reflection inside the water → droplet. If the drops are large, 1 millimeter or more in diameter, red, green, and violet are bright but there is little blue.

As the droplets get smaller, red weakens.

Rainbows are not seen in midday since the whole 42° circle is below the horizon at most latitudes. So rainbows tend to be seen most in the later afternoon when a thundershower has passed and the Sun is illuminating from the west.

primary; → rainbow.

primary star
  ستاره‌ی ِ نخستان   
setâre-ye naxostân

Fr.: étoile principale   

In a → multiple star system, the most massive → component. In other words, the star nearest to the system's → center of garvity.

primary; → star .

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