| time measured by the diurnal motion of stars. A sidereal day is about four minutes shorter than a solar day, with hours, minutes, and seconds all proportionally shorter. |
| sidereal time n. Time based on the rotation of the earth with reference to the background of stars. |
sidereal time
time as measured by the apparent motion about the Earth of the distant, so-called fixed, stars, as distinguished from solar time, which corresponds to the apparent motion of the Sun. The primary unit of sidereal time is the sidereal day, which is subdivided into 24 sidereal hours, 1,440 sidereal minutes, and 86,400 sidereal seconds. Astronomers rely on sidereal clocks because any given star will transit the same meridian at the same sidereal time throughout the year. The sidereal day is almost 4 minutes shorter than the mean solar day of 24 of the hours shown by ordinary timepieces.
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