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Measurement of time based on the position of the stars, rather than the Sun. While it takes the Earth 23 hours, 56 minutes, 4.091 seconds to rotate once on its axis relative to the Sun, it takes exactly 24 hours for it to rotate once with respect to the stars. Therefore, a solar day, which is measured with respect to the Sun, is slightly shorter than a sidereal day, which is measured with respect to the stars. The difference between solar and sidereal time is due to the Earth's motion - as we move along our orbit around the Sun, the relative position of the Sun compared to the background stars changes, so the clocks shift by just a little bit each day. Astronomers use this time keeping method when they are making observations, because the current sidereal time equals the right ascension coordinate that is crossing the meridian at that moment. This makes it easy to compare the right ascension of an object and the local sidereal time to figure out the optimum time to observe an object.
Time measured with respect to the stars as opposed to the sun. 1 mean sidereal day = 23h 56m 4.09053s of mean solar time. (The Astronomical Almanac 1996 p. B6)
the measure of time defined by the apparent diurnal motion of the catalogue equinox; hence a measure of the rotation of the Earth with respect to the stars rather than the Sun.
Time on Earth measured with respect to the stars, rather than the Sun; the local hour angle of the vernal equinox.
The hour angle of the First Point of Aries. It is time measured with respect to the stars. See the tutorial on Time.
A time scale based on the true period of Earth's rotation; the time from star rise to star rise; 4 minutes shorter than the 24 hour day
is defined as the time elapsed since the most recent meridian passage of the vernal equinox. This system is based on the rotation of the Earth with respect to the stars, instead of the sun. (See solar time.) A sidereal day is slightly shorter than 24 hours (3 minutes 55.91 seconds shorter). See Jim McDonald's excellent Sidereal Time Page at the University of Connecticut for further explanation.
Time measured by the daily motion of stars.
Time relative to the stars other than the Sun.
Time measured by the rotation of the Earth with respect to the stars (rather than the rate relative to the Sun, which is this basis for civil time). Local sidereal time at a particular place is given by the right ascension of the meridian.
Star time; the hour angle of the vernal equinox. Time measured with respect to the fixed stars rather than the Sun or body orbiter.