An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 104 Search : time
Planck time
  زمان ِ پلانک   
zamân-e Planck

Fr.: temps de Planck   

The time representing the → Planck length divided by the → speed of light. It is expressed by: tP = (Għ/c5)1/2≅ 5.4 x 10-44 s, where G is the → gravitational constant, ħ is the → reduced Planck's constant, and c is the → speed of light. At the Planck time, the mass density of the Universe is thought to approach the → Planck density.

Planck; → time.

precession time
  زمان ِ پیشایان   
zamân-e pišâyân

Fr.: temps de précession   

A time interval over which an orbit precesses by 2π radians in its plane.

precession; → time.

proper time
  زمان ِ سره   
zamân-e saré (#)

Fr.: temps propre   

In general relativity, the time as measured on a clock that travels with the observer in the same system. An accelerated clock will measure shorter time intervals between events than a non-accelerated clock between the same events. → twin paradox.

proper; → time.

real-time operation
  آپارش در زمان ِ هسیا   
âpâreš dar zamân-e hasyâ

Fr.: opération en temps réel   

The operation of a computer during the actual time that the related physical processes take place so that the results can be used to guide the physical processes.

real; → time; → operation.

real-time processing
  آمایش در زمان ِ هسیا   
âmâyeš dar zamân-e hasyâ

Fr.: traitement en temps réel   

Data processing that takes place instantaneously upon data entry or receipt of a command.

real; → time; → processing.

recombination time
  زمان ِ بازمیازش   
zamân-e bâzmiyâzeš

Fr.: temps de recombinaison   

The time period necessary for a cloud of atomic hydrogen to be → ionized by the ultraviolet photons of a central → massive stars.

recombination; → time.

relaxation time
  زمان ِ واهلش   
zamân-e vâhaleš

Fr.: temps de relaxation   

The characteristic length of time that is required for a system undergoing → relaxation to move to its equilibrium state. If the system follows an exponential law G = G0 exp(-t / τ), the relaxation time is the time required for G to obtain the fraction 1/e of its initial value G0.

relaxation; → time.

response time
  زمان ِ پاسخ   
zama-e pâsox

Fr.: temps de réponse   

The time between an occurrence and a reaction produced by the occurrence.

response; → time.

Shapiro time delay
  درنگ ِ شپیرو   
derang-e Shapiro

Fr.: effet Shapiro   

A → general relativity effect whereby an → electromagnetic signal passing near a massive object takes, due to the curved → space-time, a slightly longer time to travel to a target than it would if the mass of the object were not present. The Shapiro time delay is one of the four classic solar system tests of general relativity. Radar reflections from → Mercury and → Mars are consistent with general relativity to an accuracy of about 5%. The Shapiro time delay is a significant contributor in → gravitational lens systems.

Irwin I. Shapiro, an American astrophysicist; → time; → delay.

sidereal time
  زمان ِ اختری   
zamân-e axtari (#)

Fr.: temps sidéral   

The time based upon → Earth's rotation with respect to the stars, with the → sidereal day as the unit of measurement. At the moment when the → vernal equinox crosses the → meridian in → upper culmination, sidereal time is equal to zero hours for that observing position. The → hour angle of the vernal equinox is equal to sidereal time.

sidereal; → time.

solar time
  زمان ِ خورشیدی   
zamân-e xoršidi (#)

Fr.: temps solaire   

The time based on the rotation of the Earth relative to the Sun. → mean solar time.

solar; → time.

space-time
  فضا-زمان   
fazâ-zamân (#)

Fr.: espace-temps   

A physical entity resulting from the union of space and time concepts. In its most simple version space-time is the four-dimensional continuum, having three spatial coordinates and one temporal coordinate, in which any → event or physical object is located. In → special relativity it is Minkowski's flat space-time. In → general relativity, it is described by a curved entity characterized by a → metric. Free-fall motion describes the → geodesic of this curved space-time. It may have additional dimensions in the context of speculative theories, such as → string theory.

space; → time.

space-time curvature
  خمیدگی ِ فضا-زمان   
xamidegi-ye fazâ-zamân

Fr.: courbure de l'espace-temps   

curvature of space-time.

space; → time; → curvature.

space-time diagram
  نمودار ِ فضا-زمان   
nemudâr-e fazâ-zamân (#)

Fr.: diagramme espace-temps   

A simple way of representing the → space-time continuum, usually including time and only one spatial dimension. The curve of a particle's equation of motion on a space-time diagram is called a → world line. Same as → Minkowski diagram.

space; → time; → diagram.

space-time interval
  اندروار ِ فضا-زمان   
andarvâr-e fazâ-zamân

Fr.: intervalle espace-temps   

1) In Einstein's → theory of relativity, ds2 = c2dt2 - dx2 - dy2 - dz2.
2) In → Newtonian mechanics, time interval: dt; space interval at fixed time: dl2 = dx2 + dy2 + dz2.

space-time; → interval.

spacetime
  فضا-زمان   
fazâ-zamân

Fr.: espace-temps   

space-time.

space; → time.

speckle lifetime
  عمر ِ پَکال   
omr-e pakâl

Fr.: durée de vie de tavelures   

The time scale on which a stellar image changes significantly due to → atmospheric turbulence. It is proportional to the ratio r0/Δv, where r0 is the → Fried parameter and Δv the standard deviation of the distribution of wind velocities weighted by the turbulence structure coefficient. Typical lifetimes in the visible range from about 3 to 30 milliseconds.

speckle; → life; → time.

Omr "life-time;" from Ar. 'umr; pakâl, → speckle.

standard time
  زمان ِ استانده   
zamân-e estândé

Fr.: temps standard   

The time in any of the 24 internationally agreed time zones into which the Earth's surface is divided. The primary zone is centered on the Greenwich meridian (0° longitude).

standard; → time.

star formation time scale
  مرپل ِ زمانی ِ دیسش ِ ستاره   
marpel-e zamâni-ye diseš-e setâre

Fr.: échelle de temps de formation d'étoiles   

The time necessary for a star to form. It depends inversely on the stellar mass.

star formation; → time scale.

stationary time series
  سری ِ زمانی ِ ایست‌ور   
seri-ye zamâni-ye istvar

Fr.: série temporelle stationnaire   

A → time series if it obeys the following criteria: 1) Constant → mean over time (t). 2) Constant → variance for all t, and 3) The → autocovariance function between Xt1 and Xt2 only depends on the interval t1 and t2.

stationary; → time; → series.

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