sidereal day

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The duration of one rotation of the earth on its axis, with respect to the vernal equinox over the upper branch of a meridian. Because of the precession of the equinoxes, the sidereal day thus defined is slightly less than the period of rotation with respect to the stars, but the difference is less than 0.01 second. The length of the sidereal day is 24 hours of sidereal time or 23h 56m 04.091s of mean solar time.

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