sidereal time

sidereal time (ST), time measured relative to the fixed stars; thus, the sidereal day is the period during which the earth completes one rotation on its axis so that some chosen star appears twice on the observer's celestial meridian. Because the earth moves in its orbit about the sun, the sidereal day is about 4 min shorter than the solar day (see solar time). Thus, a given star will appear to rise 4 min earlier each night, so that different stars are visible at different times of the year. The local sidereal time of an observer is equal to the hour angle of the vernal equinox.

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.

More on sidereal time from Fact Monster:

  • sidereal period - sidereal period sidereal period, in astronomy, length of time a body takes to complete an orbit ...
  • hour angle - hour angle hour angle, in astronomy, a coordinate in the equatorial coordinate system. The hour ...
  • transit instrument - transit instrument transit instrument or transit,telescope devised to observe stars as they cross ...
  • day - day day, period of time for the earth to rotate once on its axis. The ordinary day, or solar day, ...
  • equatorial coordinate system - equatorial coordinate system equatorial coordinate system, the most commonly used astronomical ...

See more Encyclopedia articles on: Astronomy: General