apparent sidereal day
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 time
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.
Greenwich Apparent Sidereal Time (GAST)
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)
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
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
šomâre-ye ruz-e axtari-ye Greenwich
Fr.: nombre du jour sidéral de Greenwich
The integral part of the → Greenwich sidereal date.
local sidereal time
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.
lunar sidereal orbital period
dowre-ye madâri-ye axtari-ye mâng
Fr.: période orbitale sidérale de la Lune
Same as → sidereal month.
mean sidereal day
ruz-e axtari-ye miyângin
Fr.: jour sidéral moyen
The average time interval between two successive → upper transits of the → mean equinox.
mean sidereal time
zamân-e axtari-ye miyângin (#)
Fr.: temps sidéral moyen
The hour angle of the mean equinox for a given observer.
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 setâré→ star.
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 hour angle
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.
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.
dowre-ye axtari (#)
Fr.: période sidérale
→ sidereal revolution period; → sidereal rotation period.
sidereal revolution period
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 periods of the solar system planets, interms of the sidereal year, are as follows: Mercury 0.240846 (87.9691 days); Venus 0.615 (225 days); Earth 1 (365.25636 solar days); Mars 1.881; Jupiter 11.86; Satrurn 29.46; Uranus 84.01; and Neptune 164.8. That of the Moon is 0.0748 (27.32 days) and for → Sedna 12050.
→ sidereal; → revolution; → period.
sidereal rotation period
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.
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.
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.
true sidereal time
zamân-e axtari-ye râstin
Fr.: temps sidéral vrai
The → sidereal time with respect to the → true equinox.