An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 42 Search : top
protoplanetary disk
  گرده‌ی ِ پوروا-سیاره‌ای   
gerde-ye purvâ-sayyâreyi

Fr.: disque protoplanétaire   

A → circumstellar disk of gas and dust surrounding a → pre-main sequence star from which planetary systems form. Protoplanetary disks are remnants of → accretion disks which bring forth stars. Typically, their sizes are ~100-500 AU, masses ~10-2 solar masses, lifetimes ~106-107 years, and accretion rates ~10-7-10-8 solar masses per year. According to the standard theory of planet formation, called core accretion, planets come into being by the growth of → dust grains which stick together and produce ever larger bodies, known as → planetesimals. The agglomeration of these planetesimals of 100 to 1000 km in size into rocky Earth-mass planets is the main outcome of this theory. Beyond the → snow line in the disk, if the masses of these cores of rock and ice grow higher than 10 times that of Earth in less than a few million years, gas can rapidly accrete and give rise to giant gaseous planets similar to → Jupiter. If core building goes on too slowly, the disk gas dissipates before the formation of → giant planets can start. Finally the left-over planetesimals that could not agglomerate into rocky planets or core of giant planets remain as a → debris disk around the central object that has become a → main sequence star. An alternative to core accretion theory is formation of planets in a massive protoplanetary disk by → gravitational instabilities. The validity of these two theories is presently debated. See also → protoplanet.

protoplanet; → disk.

protoplanetary nebula
  پیش-میغ ِ سیاره‌ای   
piš-miq-e sayyâre-yi

Fr.: pré-nebuleuse planétaire   

preplanetary nebula.

proto-; → planetary; → nebula.


Fr.: protoplasme   

The fluid substance within the living cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts.

proto- + -plasm, → plasma.

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

Fr.: isotope radioactif   

A → nuclide that is radioactive.

radioactive; → isotope.


Fr.: radioisotope   

A synonym for radionuclide.

radio; → isotope.

scotopic vision
  دید ِ تاریکی   
did-e târiki

Fr.: vision scotopique   

Vision that occurs when the eye is dark-adapted. In scotopic vision, the level of luminance is so low that the retinal cones are not stimulated, and there is no color vision. Same as scotopia; → dark adaptation.

Scotopic, from L. Gk. skoto- combining form of skotos "darkness" + -opia akin to ope "view, look," ops "eye, face;" → vision.

Did, → vision; târiki noun from târik "dark," Mid.Pers. târig "dark," târ "darkness," Av. taθra- "darkness," taθrya- "dark," cf. Skt. támisrâ- "darkness, dark night," L. tenebrae "darkness," Hittite taš(u)uant- "blind," O.H.G. demar "twilight."

spinning top
  فرموک، فرفره   
farmuk (#), ferferé (#)

Fr.: toupie   

A toy that with a quick or vigorous twist spins around its symmetry axis and balances on a point. Suppose a top is perfectly fashioned so that its → rotation axis passes through its → center of mass. If it is spun carefully such that it remains perfectly upright while rotating, it will spin at a steady → angular velocity almost indefinitely in the absence of → friction. Rotation creates an → angular momentum which is directed upward along the rotation axis, opposite to the → gravity vector. However, a slight mismatch between the rotation axis and the center of mass causes gravity to exert a → torque on the top due to its weight, acting through the center of mass. The torque gives rise to a time rate of change of angular momentum, so the top experiences → precession about its point of contact. The tip of the angular momentum vector can be perceived as precessing about the → vertical, thus describing the → precessional circle. The top's precession period is given by: Tp = (4π2I)/(mgrTs), where I is the → moment of inertia, m the mass of the top, g gravity, r the distance between the center of mass and the contact point, and Ts is the spinning period of the top. Precession is accompanied by another oscillatory phenomenon, called → nutation. Nutation is less influenced by the gravity torque and is determined by the inertia forces acting on the spinning body.

spin; → -ing; top M.E., from O.E. top, maybe related to Fr. toupie.

Farmuk, ferferé "spinning top" (Dehxodâ), two words of unknown etymology.

  ۱) بازداشتن؛ بازداشت؛ ۲) دریچه   
1) bâzdâštan; bâzdâšt (#); 2) daricé; (#)

Fr.: diaphragme   

1) To hinder or prevent the passage of. → stopping power.
2) The diaphragm used in optical instruments to cut off the marginal portions of a beam of light passing through lenses. → field stop; → stop number.

M.E. stoppen (v.), O.E. -stoppian (in forstoppian "to stop up, stifle"); V.L. *stuppare "to stop or stuff with tow or oakum" (cf. It. stoppare, Fr. étouper "to stop with tow"), from L. stuppa "coarse part of flax, tow."

1) Bâzdâštan, bâzdâšt- "to stop, restrain, inhibit, coerce, detain," from bâz-, → re-, + dâštan "to have, hold, maintain, possess," → access.
2) Daricé, literally "small door; window," from dar "door," + -cé diminutive suffix. Dar "door," Mid.Pers. dar, O.Pers. duvara-, Av. dvar-, cf. Skt. dvár-, Gk. thura, L. fores, P.Gmc. *dur-, O.E. duru, E. door, Lith. dvaras "court-yard;" PIE *dhwer-/*dhwor- "door, gate."

stop consonant
  هم‌آوای ِ ایستی   
hamâvâ-ye isti

Fr.: consonne occulsive   

occlusive consonant.

stop; → consonant.

stop number
  وابر ِ کانونی   
vâbar-e kânuni

Fr.: rapport focal   

Same as → focal ratio.

stop; → ratio.

Vâbar, → ratio; kânuni, → focal.

stopping power
  توان ِ بازداشت   
tavân-e bâzdâšt

Fr.: pouvoir d'arrêt   

A quantity indicating the extent with which a substance absorbs a → charged particle passing through it. It is the energy lost by a → non-relativistic particle per unit length of its path in the substance.

stop; → power.

  رهاواژ، فکن‌واژ   
rahâ-vâž, fekan-vâž

Fr.: mot vide   

Computers: A very commonly used word that is normally excluded by computer search engines. Stopwords have very little informational content, such as: and, the, of, it, as, may, that, a, an, of, off, etc.

stop; → word.

Rahâ-vâž, literally "free word," from rahâ "free, set free" (O.Pers. rad- "to leave," Skt. rah-, rahati "separates, leaves," Av. razah- "isolation;" PIE *redh-) + vâž, vâžé, → word. Fekan-vâž, literally "dropped word," from fekan present stem of fekandan, afkandan "to throw, cast away;" Mid.Pers. abgandan "to throw;" O.Pers. avakan- "to throw, place on," from Proto-Iranian *kan- "to throw, place, put."

bâlâ (#)

Fr.: sommet, du haut, haut   

The highest point or part. The higher end of anything on a slope.

M.E., O.E. top "summit, crest, tuft;" cf. O.N. toppr "tuft of hair," O.Fris. top "tuft," O.Du. topp, Du. top, O.H.G. zopf "end, tip, tuft of hair," Ger. Zopf "tuft of hair."

Bâlâ "up, above, high, elevated, height" (variants boland "high, tall, elevated, sublime," borz "height, magnitude" (it occurs also in the name of the mountain chain Alborz), Laki dialect berg "hill, mountain;" Mid.Pers. buland "high;" O.Pers. baršan- "height;" Av. barəz- "high, mount," barezan- "height;" cf. Skt. bhrant- "high;" L. fortis "strong" (Fr. and E. force); O.E. burg, burh "castle, fortified place," from P.Gmc. *burgs "fortress;" Ger. Burg "castle," Goth. baurgs "city," E. burg, borough, Fr. bourgeois, bourgeoisie, faubourg; PIE base *bhergh- "high."

top-down structure formation
  دیسش ِ ساختار از بالا به پایین   
diseš-e sâxtâr az bâlâ bé pâyin

Fr.: formation des structures du haut vers le bas   

A cosmological model of → structure formation in which larger structures, such as galaxy → superclusters or perhaps even the vast → filaments and → voids, form earlier and then they fragment into smaller structures such as individual galaxies. Opposite of → bottom-up structure formation.

top; → down; → structure; → formation.

top-heavy IMF
   IMF ِ بالا-سنگین   
IMF-e bâlâ-sangin


A star formation process in which → massive stars form more abundantly than that predicted by standard models, whereby the top end of the → initial mass function is significantly flatter than the canonical → Salpeter slope.

top; → heavy; → initial mass function.


Fr.: sujet, thème   

1) The subject of a discourse or of one of its parts.
2) The main and explicit subject matter of a literary work, often composed of several themes.

From L. topica, from Gk. topikos "pertaining to a common place, of a place," from topos "a place."

Bârak, from bâre "subject, matter, meaning," as in dar bare-ye "in the matter of; about," + nuance suffix -ak.

topocentric coordinates
  هماراهای ِ جا-مرکزی   
hamârâhâ-ye jâ-markazi

Fr.: coordonées topocentriques   

A coordinate system that uses the observer's location as its central reference point. Usually, the difference in the position of an object in the sky measured using topocentric and geocentric coordinates is very small because most celestial objects are so far away. However, for nearby objects this is not true. The Sun, for example, may appear displaced as much as eight arcseconds from its geocentric position, and the Moon by as much as one degree.

Topocentric, from topo- combining form of Gk. topos "place" + centric, from → center; → coordinate.

Hamârâhâ, → coordinate; jâ-markazi "topocentric," from "place" (from Mid.Pers. giyâg "place;" O.Pers. ā-vahana- "place, village;" Av. vah- "to dwell, stay," vanhaiti "he dwells, stays;" Skt. vásati "he dwells;" Gk. aesa (nukta) "to pass (the night);" Ossetic wat "room; bed; place;" Tokharian B wäs- "to stay, wait;" PIE base ues- "to stay, live, spend the night") + markazi, of, pertaining to markaz, → center.

  توپوشناختی، توپوشناسیک   
topošenâxti, topošenâsik

Fr.: topologique   

Of or relating to → topology.

topology; → -ic; → -al

topological defect
  آک ِ توپوشناختی، ~ توپوشناسیک   
âk-e topošenâxti, ~ topošenâsik

Fr.: défaut topologique   

In → cosmological models, a stable configuration of → matter formed when the → early Universe underwent → phase transitions during which fundamental symmetries were broken. There are a number of possible types of defects, such as domain walls, → cosmic strings, → magnetic monopoles, and → texture s. Same as → cosmic defect.

topological; → defect.

topological space
  فضای ِ توپوشناختی   
fazâ-ye topošenâxti

Fr.: espace topologique   

A set X together with a collection of open subsets T that satisfies the three following conditions: 1) The empty set Ø and X are in T. 2) The intersection of a finite number of sets in T is also in T. 3) The union of an arbitrary number of sets in T is also in T.

topological; → space.

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