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: 20 Search : sidereal
apparent sidereal day
  روز ِ اختری ِ پدیدار   
ruz-e axtari-ye padidâr

Fr.: jour sidéral apparent   

The time interval between two successive → upper transits of the → true equinox of date.

apparent; → sidereal; → day.

apparent sidereal time
  زمان ِ اختری ِ پدیدار   
zamân-e axtari-ye padidâr

Fr.: temps sidéral apparent   

The → mean sidereal time corrected for the → nutation and shift in the obliquity of the ecliptic that occurs as a result of the Moon's gravitational effect. Apparent sidereal time differs from mean sidereal time in that the → true vernal equinox point is used.

apparent; → sidereal; → time.

Greenwich Apparent Sidereal Time (GAST)
  زمان ِ اختری ِ پدیدار ِ گرینویچ   
zamân-e axtari-ye padidâr-e Greenwich

Fr.: temps sidéral apparent de Greenwich   

The → Greenwich Mean Sidereal Time corrected for → nutation. Therefore, it is measured with respect to the → true vernal equinox. GAST and GMST differ by the → equation of the equinoxes.

Greenwich Meridian; → apparent; → sidereal; → time.

Greenwich Mean Sidereal Time (GMST)
  زمان ِ اختری ِ میانگین ِ گرینویچ   
zamân-e axtari-ye miyângin-e Greenwich

Fr.: temps sidéral moyen de Greenwich   

The → sidereal time related to the angle between the → prime meridian and the → mean vernal equinox, measured in the plane of the equator.

mean; → Greenwich Meridian; → sidereal; → time.

Greenwich sidereal date
  روز ِ اختری ِ گرینویچ   
ruz-e axtari-ye Greenwich

Fr.: jour sidéeal de Greenwich   

The number and fraction of → mean sidereal days elapsed on the → Greenwich meridian since 12h January 1, 4773 BC (mean sidereal).

Greenwich meridian; → sidereal; → date.

Greenwich sidereal day number
  شماره‌ی ِ روز ِ اختری ِ گرینویچ   
šomâre-ye ruz-e axtari-ye Greenwich

Fr.: nombre du jour sidéral de Greenwich   

The integral part of the → Greenwich sidereal date.

Greenwich; → sidereal; → day; → number.

local sidereal time
  زمان ِ اختری ِ محلی   
zamân-e axtari-ye mahali

Fr.: temps sidéral local   

Local time measured by the apparent motion of the stars. It is the most useful form of sidereal time since it gives the right ascension of a transiting celestial object at a given location.

local; → sidereal; → time.

lunar sidereal orbital period
  دوره‌ی ِ مداری ِ اختری ِ مانگ   
dowre-ye madâri-ye axtari-ye mâng

Fr.: période orbitale sidérale de la Lune   

Same as → sidereal month.

lunar; → sidereal; → orbital; → period.

mean sidereal day
  روز ِ اختری ِ میانگین   
ruz-e axtari-ye miyângin

Fr.: jour sidéral moyen   

The average time interval between two successive → upper transits of the → mean equinox.

mean; → sidereal; → day.

mean sidereal time
  زمان ِ اختری ِ میانگین   
zamân-e axtari-ye miyângin (#)

Fr.: temps sidéral moyen   

The hour angle of the mean equinox for a given observer.

mean; → sidereal; → time.

sidereal
  اختری   
axtari (#)

Fr.: sidéral   

Of, relating to, or determined by or from stars.

From M.Fr. sidereal, from L. sidereus "starry, astral," from sidus (genitive sideris) "star, constellation."

Axtari, pertaining to axtar "star," probably a variant of setâréstar.

sidereal day
  روز ِ اختری   
ruz-e axtari (#)

Fr.: jour sidéral   

The period of → Earth's rotation around its axis, the mean value of which is about 23h 56m 04.092s (23.934 470 hours). In other words, the interval between two successive passages of a star across a given → meridian. The sidereal day is 3 minutes 56 seconds shorter than the → mean solar day. The reason is that Earth moves a little less than a degree around the Sun during the time it takes for one full axial rotation. So, for the Sun to appear on the same meridian in the sky again after one full axial rotation, the Earth has to rotate one extra degree to bring the Sun into the same apparent meridian in the sky. This is also why the stars rise and set about 4 min earlier each day.

sidereal; → day.

sidereal hour angle
  زاویه‌ی ِ ساعتی ِ اختری   
zâviye-ye sâ'ati-ye axtari (#)

Fr.: angle horaire   

The angle on the celestial sphere measured westward from the hour circle of the vernal equinox to that of the celestial body.

sidereal; → hour angle.

sidereal month
  ماه ِ اختری   
mâh-e axtari (#)

Fr.: mois sidéral   

The time taken by the Moon to complete one → revolution around the Earth with respect to a background, → fixed star. The average time is 27.321 661 days (27d 7h 43m 11.5s). Same as → lunar sidereal orbital period.

sidereal; → month.

sidereal period
  دوره‌ی ِ اختری   
dowre-ye axtari (#)

Fr.: période sidérale   

sidereal revolution period; → sidereal rotation period.

sidereal; → period.

sidereal revolution period
  دوره‌ی ِ گردش ِ اختری   
dowre-ye gardeš-e axtari (#)

Fr.: période de révolution sidérale   

The time taken by a planet or satellite to complete one revolution about its primary with respect to stars. For Earth, same as → sidereal year.

sidereal; → revolution; → period.

sidereal rotation period
  دوره‌ی ِ چرخش ِ اختری   
dowre-ye carxeš-e axtari

Fr.: période de rotation sidérale   

The rotation period of a celestial body with respect to fixed stars. For Earth, same as → sidereal day.

sidereal; → rotation; → period.

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.

sidereal year
  سال ِ اختری   
sâl-e axtari (#)

Fr.: année sidérale   

The interval between two successive passages of the Sun, in its apparent → annual motion around the → celestial sphere, through a particular point relative to stars. It is equal to 365.256356 days for the J2000.0 epoch and is 20m 24.5s longer than the → tropical year.

sidereal; → year.

true sidereal time
  زمان ِ اختری ِ راستین   
zamân-e axtari-ye râstin

Fr.: temps sidéral vrai   

The → sidereal time with respect to the → true equinox.

true; → sidereal; → time.