Children's, Intermediate and Advanced Online English Dictionary & Thesaurus

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sidereal day a unit of time equal to the time required for one rotation of the earth; twenty-three hours, fifty-six minutes, and 4.1 seconds.
sidereal month the time required for one complete revolution of the moon around the earth with respect to a fixed star, or about 27.3 days in mean solar time.
sidereal time time based upon the rotation and revolution of the earth with reference to the background of stars.
sidereal year a unit of time equal to the time required for one revolution of the earth around the sun; 365 days, six hours, nine minutes, and 9.54 seconds.