An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 40 Search : top
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.

catoptric light
  نور ِ بازتابیک   
nur-e bâztâbik

Fr.: lumière catoptrique   

Light that is reflected from a curved surface mirror.

catoprtics; → light.

catoptric system
  راژمان ِ بازتابیک   
râžmân-e bâztâbik

Fr.: système catoprtique   

An optical system in which the light is reflected only.

catoprtics; → system.


Fr.: catroptique   

The area of → optics which treats of the laws and properties of light reflected from reflective surfaces.

From Gk. katoptrikos, from katoptron "mirror" (from kat-, → cata-, + op- "to see," → optics, + -tron suffix of instruments) + -ikos, → -ics.

Bâztâbik, from bâztâb, → reflection, + -ik, → -ics.

fertile isotope
  ایزوتوپ ِ بارور   
izotop-e bârvar

Fr.: isotope fertile   

An → isotope not itself → fissile but that is converted into a fissile isotope, either directly or after a short → decay process following absorption of a → neutron. Example: U-238 can capture a neutron to give U-239. U-239 then decays to Np-239 which in turn decays to fissile Pu-239. The most important fertile isotope is U-238. This is by far the most abundant isotope of natural uranium, making up 99.28%. The important transformation chain is: 92U238 + 0n193Np239 + β- (23.5 minutes) → 94Pu239 + β- (2.36 days).

fertile; → isotope .

field stop
  دریچه‌ی ِ میدان   
darice-ye meydân

Fr.: diaphragme de champ   

A diaphragm located at an image plane of an optical system that determines the size and shape of the image. → aperture stop.

field; → stop.

fissile isotope
  ایزوتوپ ِ شکافت‌پذیر   
izotop-e šektpazir

Fr.: isotope fissile   

An isotope that is capable of undergoing nuclear fission after capturing either fast neutron or thermal neutron. Typical fissionable isotopes: 238U, 240Pu, but also 235U, 233U, 239Pu, 241Pu

fissile; → isotope .

  ایزوتوپ، همجا   
izotop (#), hamjâ (#)

Fr.: isotope   

One of two or more atoms having the same number of protons in its nucleus, but a different number of neutrons and, therefore, a different mass.

Isotope, from → iso- + -tope, from Gk. topos "place."

Izotop, loan from Fr., as above. hamjâ, from ham- "together" → com- + "place" (from Mid.Pers. giyag "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").

isotope fractionation
  برخانش ِ ایزوتوپی   
barxâneš-e izotopi

Fr.: fractionnement isotopique   

A slight difference between the → abundances of → isotopes of the same → chemical element owing to → physical or → chemical  → processes. It results in the → enrichment or → depletion of an isotope. Same as → isotopic fractionation.

isotope; → fractionation

isotope shift
  کیب ِ ایزوتوپی   
kib-e izotopi

Fr.: décalage isotopique   

A displacement in the spectral lines due to the different isotopes of an element.

isotope; → shift.

izotopi (#)

Fr.: isotopique   

Of or relating to an → isotope.

isotope; → -ic.

isotopic fractionation
  برخانش ِ ایزوتوپی   
barxâneš-e izotopi

Fr.: fractionnement isotopique   

Same as → isotope fractionation.

isotopic; → fractionation

isotopic number
  عدد ِ ایزوتوپی   
adad-e izotopi

Fr.: nombre isotopique   

The difference between the number of neutrons in an isotope and the number of protons. Neutron excess.

isotopic; → number.

isotopic ratio
  وابر ِ ایزوتوپی   
vâbar-e izotopi

Fr.: rapport isotopique   

The relative abundances of two isotopes of a given chemical element, such as D/H (deuterium/hydrogen), (carbon) 12C/13C, and (uranium) 235U/238U.

isotopic; → ratio.

isotopic spin
  اسپین ِ ایزوتوپی، ایزو-اسپین   
spin-e izotopi (#), izospin (#)

Fr.: spin isotopique   

Same as → isospin.

isotopic; → spin.


Fr.: isotopologue   

Any of molecular entities which differ in their isotopic composition but retain the same → chemical elements, e.g. H2O and HDO.

Abbreviation of → isotopic → analogue.


Fr.: isotopomère   

Any of → isomers having the same number of each isotopic atom but differing in their positions. For example, CH3CHDCH3 and CH3CH2CH2D are a pair of isotopomers.

Short for isotopic isomers.


Fr.: magnétopause   

The boundary layer between a planet's → magnetosphere and the → magnetic field of the → solar wind. It borders the → magnetosheath and is defined by the surface on which the pressure of the solar wind is balanced by that of the planet's magnetic field. The front point of the Earth's magnetopause, on the sun-ward side of the Earth, is about 10 terrestrial radii, on average. This point can be closer or farther, because the magnetopause contracts or expands depending on the intensity of the solar wind.

From → magneto- + pause "break, cessation, stop," from M.Fr. pause, from L. pausa "a halt, stop, cessation," from Gk. pausis "stopping, ceasing," from pauein "to stop, to cause to cease."

From meqnât-magnet + marz "frontier, border, boundary," from Mid.Pers. marz "boundary;" Av. marəza- "border, district," marəz- "to rub, wipe;" Mod.Pers. parmâs "contact, touching" (→ contact), mâl-, mâlidan "to rub;" PIE base *merg- "boundary, border;" cf. L. margo "edge" (Fr. marge "margin"); Ger. Mark; E. mark, margin.


Fr.: protoplanète   

A stage in the formation of a → planet, which comes about from the aggregation of → planetesimals. The protoplanet eventually becomes a planet by → accretion of material from a → protoplanetary disk.

proto- + → planet.

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.

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