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: 23 Search : active
active
  ژیرا   
žirâ

Fr.: actif   

1) Being in a state of action; not quiescent.
2) Functioning or capable of functioning.
3) Marked by vigorous activity.

M.Fr. actif, from L. activus, from actus, p.p. of agere, → act.

Žirâ, adj. from stem žir, → act + suffix .

active galactic nucleus (AGN)
  هسته‌ی ِ کهکشان ِ ژیرا   
haste-ye kahkašân-e žirâ

Fr.: noyau actif de galaxie   

A central region of an → active galaxy, which is a → light-year or less in diameter and has an abnormally high luminosity. The nucleus emits high energy radiation (→ gamma rays, → X-rays, → ultraviolet) and shows → variability over various time-scales, sometimes very short (hours to weeks). Emission line spectra reveal high velocity motions up to 104 km s-1. AGNs are divided into two main types. Type I refers to an AGN whose nucleus is visible (the spectra has both narrow and broad emission lines), while in type II AGN, the broad line region (BLR) is obscured and the lines are very narrow. This may be due either to the viewing angle or some intrinsic difference in structure. See also → broad-line region, → narrow-line region, → quasar.

active; → galactic; → nucleus.

active galaxy
  کهکشان ِ ژیرا   
kahkašân-e žirâ

Fr.: galaxie active   

A galaxy that produces huge amounts of energy at its center, which cannot be attributed to normal processes from stars, interstellar medium, and their interactions. There are several types of active galaxies: → Seyfert galaxies, → quasars, and → blazars. All of these objects show brightness variations, some as short as 3 hours. These fluctuations indicate a relatively very small size for the central object, because an object cannot vary in brightness faster than light can travel across it. For example, an object that is one → light-year in diameter cannot vary significantly in brightness over a period of less than one year.

active; → galaxy.

active optics
  نوریک ِ ژیرا   
nurik-e žirâ

Fr.: optique active   

A technique for improving the → resolving power of a telescope by controlling the shape of the main mirror at a relatively slow rate. The → image quality is optimized automatically through constant adjustments by in-built corrective → actuators operating at fairly low temporal frequency ~0.05 Hz or less. → adaptive optics.

active; → optics.

active prominence
  زبانه‌ی ِ ژیرا   
zabâne-ye žirâ

Fr.: protubérance active   

A solar → prominence with very rapid motion (up to 2,000 km s-1), moving and changing in appearance over a few minutes of time, in contrast to a → quiescent prominence.

active; → prominence.

active region
  ناحیه‌ی ِ ژیرا   
nâhiye-ye žirâ

Fr.: région active   

An area of the Sun exhibiting → solar activity with the presence of → sunspots, → flares, → faculae, → prominences, and other phenomena associated with intense magnetic fields.

active; → region.

active sun
  خورشید ِ ژیرا   
xoršid-e žirâ

Fr.: soleil actif   

The Sun during its 11-year cycle of activity when spots, flares, prominences, and variations in radiofrequency radiation are at a maximum.

active; → sun.

attractive
  درکشنده   
darkašandé (#)

Fr.: attractif   

Having the quality of attracting.

Verbal adj. from → attract.

attractive force
  نیروی ِ درکشنده   
niru-ye darkašandé

Fr.: force attractive   

A physical force (→ gravitational, → electric, → magnetic, etc.) by which a body attracts another.

attractive; → force.

inactive
  ناژیرا   
nâžirâ

Fr.: inactif   

1) Not → active.
2) Chem.: Not → reactive.

in-; → active.

interactive
  اندرژیری   
andaržiri

Fr.: interactif   

1) Acting one upon or with the other.
2) Computers: Of or pertaining to a system or program that maintains an exchange with the user, alternately accepting input and then responding.

inter-; → active.

optically active
  نورانه ژیرا   
nurâné žirâ

Fr.: optiquement actif   

Relating to → optical activity.

optically; → active.

radioactive
  پرتو-ژیرا   
partow-žirâ

Fr.: radioactive   

Possessing, or pertaining to, → radioactivity.

radio + → active.

radioactive dating
  سن‌یابی ِ پرتو-ژیرا   
sen yâbi-ye partow-žirâ

Fr.: datation radioactive   

Determining the age of an object from the → radioactive decay of its constituting material. The technique consists of comparing the → abundance ratio of a → radioactive isotope to its → decay product. This will yield the number of half-lives that have occurred since the sample was formed. More specifically, if an object is made up of 50 % decay product then it has gone through 1 → half-life. 75% decay product equals 2 half-lives, 87.5% decay product equals 3 half-lives, 93.76% decay product equals 4 half-lives, and so on. For example, the decay product of → uranium-238 (238U) is → lead-206 (206Pb). The half-life of 238U is 4.5 billion years. Hence, if the sample has gone through two half-lives, it is 9 billion years old. See also: → radiocarbon dating.

radioactive; → dating.

radioactive decay
  تباهی ِ پرتو-ژیرا   
tabâhi-ye partow-žirâ

Fr.: désintégration radioactive   

Spontaneous emission by a nucleus of photons or particles.

radioactive; → decay.

radioactive isotope
  ایزوتوپ ِ پرتو-ژیرا   
izotop-e partow-žirâ

Fr.: isotope radioactif   

A → nuclide that is radioactive.

radioactive; → isotope.

radioactive nuclide
  هسته‌وار ِ پرتو-ژیرا   
hastevâr-e partowžirâ

Fr.: nucléide radioactif   

A → nuclide that disintegrates by emitting radiation and transforms into another nuclide. Same as → radionuclide.

radioactive; → nuclide.

radioactive waste
  آخال ِ پرتو-ژیرا   
âxâl-e partow-žirâ

Fr.: déchets radioactifs   

The radioactive by-products from the operation of a nuclear reactor or from the reprocessing of depleted nuclear fuel. Also known as nuclear waste.

radioactive; → waste.

reactive
  واژیرنده؛ واژیرشی   
vâžirandé; vâžireši

Fr.: réactif   

Tending to react. Pertaining to or characterized by reaction.

From → react + -ive a suffix of adjectives expressing tendency, disposition, function, connection, etc.

Vâžirandé verbal adj. of vâžiridanreact; vâžireši, adj. of vâžirešreaction.

refractive index
  دیشن ِ شکست   
dišan-e šekast

Fr.: indice de réfraction   

Of any optical medium, the ratio of the → speed of light in vacuum (c) to that in the medium (v): n = c/v. The refractive index for vacuum, by definition, is 1. The refractive index of air is 1.00029 at standard temperature (25 °C) and pressure (1 atm). The refractive index of a medium depends on the wavelength of refracted wave. With light waves, n increases as the wavelength decreases. → Snell's law can be used to derive n. Same as → index of refraction.

Refractive, pertaining to → refraction; → index.

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