An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



<< < abs arg Cop dis Ham hyp int Mod per per per per per per pro Sma sup sup sup ten upp > >>

Number of Results: 418 Search : per
absolute permeability
  تراوایی ِ اوست   
tarâvâyi-ye avast

Fr.: perméabilité absolue   

magnetic permeability.

absolute; → permeability.

absolute temperature
  دما‌ی ا َوَست   
damâ-ye avast

Fr.: température absolue   

Also called → thermodynamic temperature, the value of a → temperature in the → Kelvin scale. It is is equal to the temperature on the → Celsius scale -273.15 °C.

absolute; → temperature.

adiabatic temperature gradient
  زینه‌ی ِ دمای ِ بی‌دررو   
zine-ye damâ-ye bidarrow

Fr.: gradient de température adiabatique   

The temperature gradient defining the → radiative equilibrium condition in a region. It is expressed as: dT/dr = (1 - 1/ γ)((T / P)(dP / dr), where T and P are temperature and pressure, dT / dr and dP / dr temperature and pressure gradients respectively, and γ = CP / CV. For radiative equilibrium to be stable against → convection, the actual temperature gradient must be less than the adiabatic temperature gradient, i.e. |dT /dr|rad < |dT /dr|ad. See also → Schwarzschild's criterion.

adiabatic; → temperature; → gradient.

advance of perihelion
  پیشرفت ِ پیراهور   
pišraft-e pirâhur

Fr.: avance du périhélie   

The slow rotation of the major axis of a planet's orbit in the same direction as the revolution of the planet itself, due mainly to gravitational interactions with other planets. The perihelion of the planet Mercury advances about 9'.6 per century. The bulk of the advance was accounted by perturbations from other planets. However, a remaining small advance, by 43'' per century, was eventually explained as an effect predicted by Einstein's theory of → general relativity. In the case of close binary stars, the advance of pericenter may additionally be caused by mass transfer and the stars' distorted (elliptical) shapes. Advance of perihelion (or pericenter) is also known as → apsidal motion.

Advance, from O.Fr. avancer "move forward," from V.L. *abantiare, from L.L. abante "from before," from ab- "from" + ante "before," PIE *ant- "front, forehead;" → perihelion.

Pišraft "advance," from piš "forward; in front; before," Mid.Pers. peš + raft "going; walk, travel," from raftan "to go."

Algol (β Persei)
  الغول، رأس‌الغول   
Alqul, Ra's-ol-Qul (#)

Fr.: Algol   

A variable star in the constellation → Perseus, which was the first eclipsing binary discovered. Its brightness varies between 2.2 and 3.5 magnitudes. Lying at a distance of about 82 → light-years, it consists of at least three components. The brightest component (A) is of spectral type B8 V, and the second one (B) a K type giant. The components A and B turn around each other with a period of about 68.8 hours.

Algol, from Ar. Ra's al-ghul "the ghoul's head".

ampere (#)

Fr.: ampère   

The → SI unit of → electric current; symbol A. It is defined by taking the fixed numerical value of the → elementary charge, e, to be 1.602 176 634 × 10-19 when expressed in the unit → coulomb (C), which is equal to A s, where the → second (s) is defined in terms of ΔνCs.

Named after the French physicist and mathematician André-Marie Ampère (1775-1836), one of the pioneers in studying electricity, who laid the foundation of electromagnetic theory.

Ampere's law
  قانون ِ آمپر   
qânun-e Ampere

Fr.: loi d'Ampère, théorème ~   

One of the basic relations between → electricity and → magnetism, stating quantitatively the relation of a → magnetic field to the → electric current or changing electric field that produces it. Ampere's law states that the line integral of the magnetic field around an arbitrarily chosen path is proportional to the net electric current enclosed by the path. Also known as Ampère's theorem, Ampère's circuital law.

ampere; → law.

angular dispersion
  پاشش ِ زاویه‌ای   
pâšeš-e zâvie-yi

Fr.: dispersion angulaire   

The rate of change of the angles of emergence θ of various wavelengths from a dispersing prism: dθ/dλ.

angular; → dispersion.

annihilation operator
  آپارگر ِ نابودی   
âpârgar-e nâbudi

Fr.: opérateur d'annihilation   

In → quantum field theory, the operator that lowers → eigenstates one → energy level, contrarily to the → creation operator.

annihilation; → operator.

anomalous dispersion
  پاشش ِ ناسان   
pâšeš-e nâsân

Fr.: dispesrion anormale   

The phenomenon whereby the → refractive index of light in a medium changes rapidly with wavelength in the vicinity of an → absorption band. Hence the → dispersion curve of the substance shows marked deviations from → Cauchy's equation, in contrast with the behavior of → normal dispersion. On the shorter λ side of the absorption band the refractive index falls off more rapidly than required by Cauchy's equation representing values of n for visible light. On the long λ side of the absorption band the index is very high, decreasing at first rapidly and then more slowly as one goes beyond the absorption band.

anomalous; → dispersion.

antenna temperature
  دما‌ی ِ آنتن   
damâ-ye ânten

Fr.: température d'antenne   

In radio astronomy, a measure of the power absorbed by the antenna. In an ideal, loss-free radio telescope, the antenna temperature is equal to the brightness temperature if the intensity of the received radiation is constant within the main lobe. → antenna; → temperature.

antenna; → temperature.

aperiodic damping
  میرایی ِ نادوره‌ای   
mirâyi-ye nâdowreyi

Fr.: amortissement apériodique   

A system in which the → damping is great enough to prevent oscillation.

Aperiodic, from → a- + periodic; + → damping.

dahâné (#)

Fr.: ouverture   

The diameter of the → primary mirror in a → reflecting telescope, the → objective lens in a → refracting telescope, the → dish of a → radio telescope, or the → entrance pupil of an instrument such as → spectrograph or → photometer.

From L. apertura, from apertus, p.p. of aperire "to open, uncover," from PIE *ap-wer-yo- from *ap- "off, away" + base *wer- "to cover".

Ddahâné "an opening," from dahân, → mouth.

aperture efficiency
  کار‌آیی ِ دهانه   
kârâyi-ye dahâné

Fr.: efficacité d'ouverture   

The ratio of the → effective aperture of a radio telescope to the true aperture.

aperture; → efficiency.

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.

aperture ratio
  وابر ِ دهانه   
vâbar-e dahâné

Fr.: rapport d'ouverture   

The ratio of the effective diameter of a lens or mirror to its focal length.

aperture; → ratio.

aperture stop
  دریچه‌ی ِ دهانه   
darice-ye dahâné

Fr.: diaphragme d'ouverture   

The diaphragm that limits the diameter of the axial light bundle allowed to pass through a lens.

aperture; → stop.

aperture synthesis
  هندایش ِ دهانه   
handâyeš-e dahâné

Fr.: synthèse d'ouverture   

The method of combining the signals received by several smaller telescopes distributed over a very large area or baseline to provide the high angular resolution of a much large telescope.

aperture; → synthesis.


Fr.: aperception   

In psychology of education, the fundamental process in acquiring knowledge, and the part played by existing knowledge.

From Fr. aperception, from N.L. apperceptionem, from ap- variant of → ad- before p + → perception.

From prefix bar- "on, upon, up" (Mid.Pers. abar; O.Pers. upariy "above; over, upon, according to;" Av. upairi "above, over," upairi.zəma- "located above the earth;" cf. Gk. hyper- "over, above;" L. super-; O.H.G. ubir "over;" PIE base *uper "over") + âgerteš, → perception.

argument of periapsis
  آروزمان ِ پیراهباک   
âruzmân-e pirâhabâk

Fr.: argument du périastre   

The angular distance between the → ascending node of an object orbiting a → primary and its periapsis measured from the primary. Argument of periapsis is measured in the → orbital plane in the direction of motion. It is one of the → orbital elements. See also → argument of perigee, → argument of perihelion.

argument; → perigee.

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