An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 998
period-luminosity relation
  باز‌آنش ِ دوره-تابندگی   
bâzâneš-e dowré-tâbandegi

Fr.: relation période-luminosité   

A correlation between the periods and luminosities of → Cepheid variable stars. Once the period of a Cepheid variable is determined from observations, the period-luminosity relation can be used to derive its luminosity. Since luminosity is a function of distance, the distance can then be calculated with the luminosity. The period-luminosity relation is an invaluable tool for the measurements of distances out to the nearest galaxies and thus for studying the structure of our own Galaxy and of the Universe. The relation was discovered by Henrietta Leavitt in 1912 when studying Cepheids in the → Small Magellanic Cloud.

period; → luminosity; → relation.

period-mean density relation
  باز‌آنش ِ دوره-چگالی ِ میانگین   
bâzâneš-e dowré-cagâli-ye miyângin

Fr.: relation période-densité moyenne   

A relation that gives a rough estimate of the oscillation period of a → pulsating star as a function of its mean density. This relation is obtained by considering how long it would take a sound wave to travel across the diameter of a model star: Π ≅ (3π/2γGρ)1/2, where ρ is the mean density, γ the ratio of → specific heats (Cp/Cv), and G the → gravitational constant. This relation shows that the pulsation period of a star is inversely proportional to the square root of its mean density. And this is the reason why the pulsation periods decrease along the → instability strip from the luminous, very tenuous → supergiants to the faint, very dense → white dwarfs.

period; → mean; → density; → relation.

dowreyi (#)

Fr.: périodique   

Recurring at regular intervals of time.

Adjective of → period.

periodic comet
  دنباله‌دار ِ دوره‌ای   
dombâledâr-e dowreyi

Fr.: comète périodique   

A comet with a period of less than 200 years. Also called short-period comet.

periodic; → comet.

periodic function
  کریای ِ دوره‌ای   
karyâ-ye dowreyi

Fr.: fonction périodique   

A function f(x) if for all x, f(x + P) = f(x), where P is a positive constant. The least value of P > 0 is called the period of f(x).

periodic; → function.

periodic motion
  جنبش ِ دوره‌ای   
jonbeš-e dowreyi

Fr.: mouvement périodique   

Any motion that recurs in identical forms at equal intervals of time.

periodic; → motion.

periodic system
  راژمان ِ دوره‌ای   
râžmân-e dowreyi

Fr.: système périodique   

Arrangement of the → chemical elements in the → periodic table.

periodic; → system.

periodic table
  جدول ِ دوره‌ای   
jadval-e dowreyi (#)

Fr.: tableau périodique   

An arrangement of the → chemical elements in order of their → atomic numbers in such a way as to demonstrate periodic similarities and trends in physical and chemical properties. Elements with similar properties are arranged in the same column (called a group), and elements with the same number of → valence electrons, or number of electrons in the outer shell, are arranged in the same row (called a period). Under the latest recommendations from IUPAC (the International Union of Pure and Applied Chemistry), the groups are labelled 1 to 18 from left to right (1988, Pure and Applied Chemistry 60, 431). Also called Mendeleev's table.
The periodic table was introduced by Dmitri Ivanovich Mendeleev (1834-1907) in 1869, who originally arranged them in order of their → atomic weights. Using the table, it was possible for Mendeleev to correct some of the atomic weights (e.g. that of beryllium) and to predict the properties of a number of elements yet to be discovered (e.g. gallium, scandium, and germanium). The British physicist Frederick Soddy (1877-1956) showed that the loss of an → alpha particle reduces the nuclear charge by two and hence lowers the atomic number by two and the position of the element in the periodic table by two groups.

periodic; → table.

periodic term
  ترم ِ دوره‌ای   
tarm-e dowre-yi

Fr.: terme périodique   

In perturbation theory used in celestial mechanics, a term that indicates a bounded disturbance which recurs regularly. → secular term.

periodic; → term.

periodic wave
  موج ِ دوره‌ای   
mowj-e dowre-yi

Fr.: onde périodique   

An oscillatory motion in which each point is repeatedly displaced at equal time intervals.

periodic + → wave.


Fr.: périodicité   

A state or condition characterized by regular repetition in time or space.

periodic + → -ity.


Fr.: périphérique   

Pertaining to, situated in, or constituting the periphery.

Adj. of → periphery.

peripheral response
  پاسخ ِ پیرابَری   
pâsox-e pirâbari

Fr.: réponse périphérique   

In a charge-coupled device, the detection of charge collected by the transport register rather than by the image-sensing elements.

peripheral; → response.

peripheral vision
  دید ِ پیرابَری   
did-e pirâbari

Fr.: vision périphérique   

In optics, the ability to see over large angles of view.

peripheral; → vision.


Fr.: périphérie   

The external surface or boundary of a body. The circumference or perimeter of any closed figure.

From, M.E., from O.Fr. periferie, from L.L. peripheria, from Gk. peripheria "circumference, outer surface," literally "a carrying around," from peripheres "rounded, moving round," peripherein "to carry or move round," from → peri- "round about" + pherein "to carry;" cognate with Pers. bordan "to carry, lead," as below.

Pirâbar, from pirâ-, → peri-, + bar present stem of bordan "to carry, lead" (Mid.Pers. burdan, O.Pers./Av. bar- "to bear, carry," barəθre "to bear (infinitive)," Skt. bharati "he carries," Gk. pherein, L. fero "to carry;" PIE base *bher- "to carry").

  پیرابین، پیرانما   
pirâbin, pirânamâ (#)

Fr.: périscope   

An optical instrument for viewing objects which are above the eye-level of the observer, or are placed so that direct vision is blocked.

peri-; + → -scope.


Fr.: pergélisol   

Layer of soil or rock, at some depth beneath the surface, in which the temperature has been continuously below 0°C from a few to several thousands of years. It exists where summer heating fails to reach the base of the layer of frozen ground.

From perma(nent) + → frost.

Mândbašm, from mând, → permanent, + bašm, → frost.

mândegâr (#)

Fr.: permanent   

Lasting or remaining without essential change.

Permanent, from M.Fr. permanent, from L. permanentem "remaining," pr.p. of permanere "endure, continue, stay to the end," from per- "through" + manere "stay," cognate with Pers. mândan, as below; → gas.

permanent gas
  گاز ِ ماندگار   
gâz-e mândegâr

Fr.: gaz permanent   

Gas which cannot be liquefied by pressure alone; gas above its critical temperature.

permanent; → gas.

permanent magnet
  آهنربای ِ ماندگار   
âhanrobâ-ye mândegâr

Fr.: aimant permanent   

A piece of magnetic material which, having been magnetized, retains a substantial proportion of its magnetization indefinitely.

permanent; → magnet.

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