An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 32 Search : period
aperiodic damping
  میرایی ِ نادوره‌ای   
mirâyi-ye nâdowreyi

Fr.: amortissement apériodique   

A system in which the → damping is great enough to prevent oscillation.

Aperiodic, from → a- + periodic; + → damping.

commissioning period
  دوره‌ی ِ راه اندازش   
dowre-ye râhandâzeš

Fr.: période de rodage   

A period during which a newly constructed observing instrument is used for test.

commissioning; → period.

long-period comet
  دمدار ِ درازدوره   
domdâr-e derâz dowré

Fr.: comète à longue période   

A comet with orbital period of more than 200 years. → short-period comet; → periodic comet.

long; → period; → comet.

long-period variable
  ورتنده‌ی ِ درازدوره   
vartande-ye derâz dowré

Fr.: variable à longue période   

A type of → variable star in which variations in brightness occur over long time-scales of months or years. The term generally refers to → Mira variable types.

long; → period; → variable.

natural period
  دوره‌ی ِ زاستاری   
dowre-ye zâstâri

Fr.: période naturelle   

Of a body or system, the period of → free oscillation.

natural; → period.

orbital period
  دوره‌یِ مداری   
dowre-ye medâri (#)

Fr.: période orbitale   

The time interval between two successive passages of an object through the same point in its orbit around another object.

orbital; → period .

dowré (#)

Fr.: période   

Physics: The duration of one complete cycle of an oscillation; the reciprocal of the frequency.
Astro.: The amount of time an astronomical body takes to complete an orbit.

From M.E. periode, from M.Fr., from M.L. periodus "recurring portion, cycle," from L. periodus "a complete sentence," from Gk. periodos "rounded sentence, cycle, circuit, period of time," literally "going around," from → peri- "around" + hodos "way, journey;" cognate with L. cedere "to go, yield."

Dowré, from dowr, from Ar. daur "age, time; revolution."

period derivative
  واخنه‌ی ِ دوره   
vâxane-ye dowré

Fr.: dérivée de la période   

The rate at which the rotation period of a → pulsar changes over time. This quantity, dP/dT, can range from as small as 0.05 picoseconds per year (1.5 x 10-21 seconds per second) to as large as about 10 milliseconds per year (4.2 x 10-10 seconds per second). For the → Crab pulsar, the period derivative is 4.2 x 10-13 s s-1, implying a decrease in the star's → rotation energy of about 4.5 x 1038 erg s-1. Period derivative is a very important parameter for the determination of the pulsar age.

period; → derivative.

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.

precession period
  دوره‌ی ِ پیشایان   
dowre-ye pišâyân

Fr.: période de précession   

The interval with which a rotating body precesses. The precession period of the Earth is 25,770 years. For a → spinning top it 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; → period.

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