An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 912

Fr.: exactitude, précision   

1) The state or quality of being → accurate.
2) The degree of nearness of a measured value to the standard or known value of the quantity, not to be confounded with → precision. For example, a refrigerator holds a constant temperature of 5.0 °C. A thermometer is used seven times to read the temperature, with the following results: 6.4, 5.1, 6.3, 4.5, 5.3, 6.1, and 4.1. This distribution does not well match the actual temperature, therefore it lacks accuracy, and shows no tendency toward a particular value; it lacks precision, as well.
If the measured temperatures are 4.8, 5.3, 5.1, 5.0, 4.6, 5.2, and 5.0, the mean value is accurate, because it comes close to the actual temperature, but the distribution shows no clear tendency toward a particular value (lack of precision).
Now suppose that the measured temperatures are 6.2, 6.3, 6.1, 6.0, 6.1, 6.3, and 6.2. In this case every measurement is well off from the actual temperature (low accuracy), but the distribution does show a tendency toward a particular value (high precision).
Finally, if the measured temperatures are 5.0, 5.0, 4.8, 5.1, 5.0, 4.9, and 5.0, the distribution is very near the actual temperature each time (high accuracy), and does show a tendency toward a particular value (high precision).
Accuracy is often given to n → significant digits or n → decimal places. For example e = 2.71828 ... = 2.718 is rounded to two four significant figures or three decimal places. → accurate to n significant figures, → accurate to n decimal places.

From L. accuratus "prepared with care, exact," p.p. of accurare "take care of," from ad- "to" + curare "take care of."

Rašmandi, from rašmand, from raš + adjective forming suffix -mand. Raš, from Av. root raz- "to right, correct, arrange;" compare with Skt. raj "to reign, rule, direct," Gk. oregein "to strech out," L. rego "to direct, lead;" PIE *reg- "to move in a straight line." Similarly, Av. râšta-, rašta- "straight," Skt. rju "straight, right, upright," Gk. orektos "elongated," L. rectus "straight," Ger. recht, E. right. In Mod.Pers. there are several derivatives: râst, râšt (as in afrâšt(an)) "right; true," rasté, rešté, raj, raž, râh, ris, râdé, radé, Lori rezg "row," etc.


Fr.: exact, précis   

1) Conforming exactly to truth or to a standard; free from error.
2) Designating → accuracy.

Accurate, from L. accuratus, → accuracy.

accurate to n decimal places
  رشمند با n رقم پس از جداگر یا ممیز   
rašmand bâ n raqam pas az jodâgar yâ momayez

Fr.: précis à n décimale, ~ avec n chiffres après la virgule, à n décimales près   

An expression specifying the number of meaningful digits to the right of the → decimal point. For example, e = 2.71828 ... = 2.718 is said to be accurate to three decimal places and 2.72 to two decimal places.

accurate; → decimal; → place.

accurate to n significant digits
  رشمند با n رقم ِ نشانار   
rašmand bâ n raqam-e nešânâr

Fr.: écrit avec n chiffres significatifs   

An expression specifying the number of meaningful digits used to express the value of a measured quantity. Same as accurate to n significant figures. For example, e = 2.71828 ... = 2.718 is rounded to four significant digits, and 2.72 to three significant digits. → accurate to n decimal places.

accurate; → significant; → digit.

Achernar (Alpha Eridani)
  آخر ِ نهر، رودپایان   
Âxer-e nahr (#), Rudpâyân

Fr.: Achernar   

The brightest star in the constellation → Eridanus. A → subgiant of → spectral type B5; apparent visual magnitude 0.5, about 140 → light-years distant (other names: HR 472, HD 10144). Recent interferometric observations show it to have a flattened shape imposed by fast rotation.

Achernar, from Ar. Axir an-Nahr "end of the river," from axir "end" + nahr "river".

Âxer-e nahr, from Axir an-Nahr.
Rudpâyân "river's end," from rud "river," → Eridanus, + pâyân "end".


Fr.: achondrite   

A class of → stony meteorites that lack → chondrules. They are made of rock that has crystallized from a molten state. Achondrites are relatively rare, accounting for about 8% of all meteorite falls.

Achondrite, from Gk. prefix a- (an- before stems beginning with a vowel or h) "not, without, lacking" + Gk. chondrite, from chondr-, from chondros "grain," + affix -ite.

  افام، بیفام   
afâm (#), bifâm (#)

Fr.: achromatique   

Of or relating to an optical system which is capable of transmitting light without decomposing it into constituent colors.

a-; → chromatic.

achromatic lens
  عدسی ِ افام، ~ بیفام   
adasi-ye afâm, ~ bifâm

Fr.: lentille achromatique   

Lens (or combination of lenses) that brings different wavelengths within a ray of light to a single focus, thus overcoming chromatic aberration.

achromatic; → lens.

asid (#)

Fr.: acide   

A substance that releases hydrogen ions to form a solution with a pH of less than 7, reacts with a base to form a salt, and turns blue litmus red.

From Fr. acide, from L. acidus "sour," adj. of state from acere "to be sour," acer "sharp, pungent, bitter;" from PIE base *ak- "sharp, pointed."

asidi (#)

Fr.: acide   

Being or containing an acid; of a solution having an excess of hydrogen atoms (having a → pH of less than 7).

acid; → -ic.

  صدایی، صداییک   
sedâyi, sedâyik

Fr.: acoustique   

Pertaining to the sense of hearing, or to → sound waves.


acoustic peak
  ستیغ ِ صداییک   
setiq-e sedâyik

Fr.: pic acoustique   

One of several peaks appearing in the → CMB angular power spectrum of the → cosmic microwave background radiation which are ripples left by acoustic oscillations of the plasma-radiation fluid in the early Universe (→ baryon acoustic oscillations). When the Universe was small and very hot, the free electron density was so high that photons could not propagate freely without being scattered by electrons. Ionized matter, electrons and radiation formed a single fluid, with the inertia provided by the baryons and the radiation pressure given by the photons.

acoustic; → peak.

acoustic pressure
  فشار ِ صدا   
fešâr-e sedâ

Fr.: pression acoustique   

Same as → sound pressure.

acoustic; → pressure.

acoustic wave
  موج ِ صدایی   
mowj-e sedâyi

Fr.: onde acoustique, ~ sonore   

A type of → longitudinal wave that consists of mechanical → vibrations of small → amplitude propagated in an → elastic medium. Acoustic waves exhibit phenomena like → diffraction, → reflection, and → interference, but not → polarization. Also called → sonic and → sound waves. See also → acoustic wave equation. The branch of physics concerned with the properties of sonic waves is called → acoustics.

acoustic; → wave.

acoustic wave equation
  هموگش ِ موج ِ صدایی   
hamugeš-e mowj-e sedâyi

Fr.: équation de l'onde acoustique   

A → differential equation that describes the time evolution of the → scalar potential of the field φ. It is expressed by: ∇2φ = (1/c2)∂2φ/∂t2, where c is → velocity of → longitudinal waves and ∇2 is the → Laplacian operator.

acoustic; → wave; → equation.

  صداییک، صداشناسی   
sedâyik, sedâšenâsi

Fr.: acoustique   

1) The study of sound, especially of its generation, propagation, and reception.
2) Those qualities of an enclosure that together determine its character with respect to distinct hearing.

From Fr. acoustique, from Gk. akoustikos "pertaining to hearing," from akoustos "heard, audible," from akouein "to hear," from copulative prefix a- + koein "to mark, perceive, hear," from PIE root *(s)keu- "to notice, observe."

Sedâyik from sedâ "sound" + Pers. suffix -ik, → -ics. Sedâ is most probably Persian, since it exists also in Indo-Aryan languages: Skt. (late Vedic): sabda "articulate sound, noise," Pali and Prakriti: sadda "sound, noise," Sindhi: sadu, sado "shout, call," Gujrâti sad "call, voice, echo," Marathi: sad "shouting to," Konkani sad "sound," Sinhali: sada "sound." Therefore, sadâ in Arabic "reverbrating noise, echo" may be borrowed from Persian, or a coincidence. Note that for the author of the classical Persian dictionary Borhân-e Qâte' (India, 1652 A.D.), the Arabic term is a loanword from Persian.

phone; →phonetics.


Fr.: acronyque   

Relating to or occurring at sunset. → heliacal

Acronical, from Gk. akronukos, from akros "tip, end," cf. Av. aγra- "top, first," Skt. agra- "first, foremost, climax" + nuks, nuktos "night," → night.

Šâmgâhi, adj. of šâmgâh "evening," from šâm "evening, evening meal" + gâh "time." The first component, šâm, from Mid.Pers. šâm "evening meal, supper," from Av. xšāfnya- "evening meal," from Av. xšap-, xšapā-, xšapan-, xšafn- "night" (O.Pers. xšap- "night," Mid.Pers. šap, Mod.Pers. šab "night"); cf. Skt. ksap- "nigh, darkness;" Hittite ispant- "night." The second component gâh "time," Mid.Pers. gâh, gâs "time," O.Pers. gāθu-, Av. gātav-, gātu- "place, throne, spot;" cf. Skt. gâtu- "going, motion; free space for moving; place of abode;" PIE *gwem- "to go, come."

acronical rising
  بر‌آیش ِ شامگاهی   
barâyeš-e šâmgâhi

Fr.: lever acronyque   

The rising of a star in the sky at or just after sunset. → heliacal rising.

acronical; → rising.

acronical setting
  فروشد ِ شامگاهی   
forušod-e šâmgâhi

Fr.: coucher acronyque   

The setting of a star at nightfall. → heliacal setting.

acronical; → setting.


Fr.: Acrux   

A southern hemisphere bright star (α Crucis) of magnitude 0.77 lying at a distance of 321 → light-years. It is apparently made up of three components. The primary component, Acrux A, is a blue subgiant of apparent magnitude 1.34 and spectral type B0.5 IV. The B component lies at about 4.1 arcsec away from the A component, which represents a distance of at least 400 AU, that is, more than 10 times the distance between the sun and planet Pluto. The C component lies about 90 arcsec away from A.

Acrux, from A, from Alpha, designating the brightest star of the constellation + crux, the constellation name. The name Acrux is probably a coinage of the American astronomer, Elijah H. Burritt, who published several editions of an astronomical atlas between 1833 and 1856.

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