An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



Number of Results: 13 Search : epoch
cosmological epoch
  زیمه‌ی ِ کیهانشناختی   
zime-ye keyhânšenâxti

Fr.: époque cosmologique   

cosmological; → epoch.

current cosmological epoch
  زیمه‌ی ِ کیهانشناختی ِ کنونی   
zime-ye keyhânšenâxti-ye konuni

Fr.: époque cosmologique actuelle   

The → Universe at the → redshift z = 0.

current; → cosmological; → epoch.

electroweak epoch
  زیمه‌ی ِ برقانزار   
zime-ye barqânezâr

Fr.: époque électrofaible   

A period in the early history of the Universe lasting from 10-36 to 10-12 seconds after the → Big Bang. The electroweak epoch begins at the same time as cosmic → inflation is triggered. This is also the time when the → strong force breaks from the → grand unified force and ends with another → phase transition will occur in which the → weak interaction breaks from the → electroweak force.

electroweak; → epoch.


Fr.: époque   

1) The date for which → orbital elements or the positions of celestial objects are calculated. Specifying the epoch is important because the apparent positions of objects in the sky change gradually due to → precession and → nutation, while orbital elements change due to the gravitational effects of the → planets. The → standard epoch used in ephemerides (→ ephemeris) and stellar catalogues at present is January 1, 2000, 12h (written also as 2000.0). See also: → Julian epoch.
2) Same as → cosmological epoch, such as → current cosmological epoch, → electroweak epoch, → epoch of thermalization, → recombination epoch, → reionization epoch.
3) A period of time usually marked by some distinctive development or series of events. See also: → polarity epoch, → epoch angle.

From M.L. epocha, from Gk. epokhe "pause, cessation, fixed point," from epekhein "to pause, take up a position," from epi- "on" + ekhein "to hold, to have;" cf. Av. hazah- "power, violence, superiority;" Skt. sahate "he masters," sáhas- "power, violence, might;" Goth. sigis; O.H.G. sigu; O.E. sige "victory;" PIE base *segh- "to hold."

Zime, from Mid.Pers. zim "time, year, winter," from Av. zyam-, zayan- "winter," probably related to zaman "time" + nuance suffix .

epoch angle
  زاویه‌ی ِ زیمه   
zâviye-ye zimé

Fr.: angle de phase initial   

Same as the → initial phase angle.

epoch; → angle.

epoch of reionization (EoR)
  زیمه‌ی ِ بازیونش   
zime-ye bâzyoneš

Fr.: époque de réionisation   

reionization epoch.

epoch; → reionization.

epoch of thermalization
  زیمه‌ی ِ یکگرمایی   
zime-ye yekgarmâyi

Fr.: époque de thermalisation   

The period during the → early Universe before the → recombination era when the photons were hot enough to ionize hydrogen. The density was so high that the interactions between → matter and → radiation were very numerous. Therefore, matter and photons were in constant contact and their → temperatures were the same. As a result, the radiation became → thermalized, i.e. the → electromagnetic spectrum of the radiation became that of a → blackbody, a process called → thermalization. Since the time of recombination the photons of → cosmic background radiation have been free to travel uninhibited by interactions with matter. Thus, their distribution of energy is a perfect → blackbody curve, as predicted by the → Big Bang theory and shown by several observations, such as → Cosmic Background Explorer (COBE), → Wilkinson Microwave Anisotropy Probe (WMAP), and → Planck Satellite.

epoch; → thermalization.

Julian epoch
  زیمه‌ی ِ یولیانی   
zime-ye Yuliyâni

Fr.: époch julienne   

A way of specifying the date as a year with a decimal based on the Julian year of 365.25 days and the Barycentric Dynamical Time (TDB). The standard epoch currently in use is J2000.0, which corresponds to January 1, 2000 12:00 Terrestrial Time.

Julian calendar; → epoch.

polarity epoch
  زیمه‌ی ِ قطبیگی   
zime-ye qotbigi

Fr.: époque de polarité   

The time during which the Earth's magnetic field was of a single polarity; an interval of time between reversals of Earth's magnetic field.

polarity; → epoch.

present epoch
  زیمه‌ی ِ کنونی   
zime-ye konuni

Fr.: époque actuelle   

Same as → present day, → today, → current cosmological epoch.

present; → epoch.

recombination epoch
  زیمه‌ی ِ بازمیازش   
zime-ye bâzmiyâzeš

Fr.: époque de recombinaison   

Same as → recombination era.

recombination; → epoch.

reionization epoch
  زیمه‌ی ِ بازیونش   
zime-ye bâzyoneš

Fr.: époque de réionisation   

An early epoch in the → Universe's history, but after the → recombination epoch, when the → first stars formed and their → ultraviolet light began to ionize the → neutral hydrogen gas that filled the Universe. The epoch of reionization is estimated to last between → redshifts of 12 to 6 (or when the Universe had between 2 and 5% of its age). Reionization marks the end of the → Dark Age in cosmic history.

reionization; → epoch.

standard epoch
  زیمه‌ی ِ استانده   
zime-ye estândé

Fr.: époque de référence   

A particular date and time that specifies the reference system to which celestial coordinates are referred. From 1984 the → Julian year is used, as denoted by the prefix J, e.g. J2000.0.

standard; → epoch.