sidereal clock

Sidereal \Si*de"re*al\, a. [L. sidereus, from sidus, sideris, a
   constellation, a star. Cf. {Sideral}, {Consider}, {Desire}.]
   1. Relating to the stars; starry; astral; as, sidereal
      astronomy.
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   2. (Astron.) Measuring by the apparent motion of the stars;
      designated, marked out, or accompanied, by a return to the
      same position in respect to the stars; as, the sidereal
      revolution of a planet; a sidereal day.
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   {Sidereal clock}, {day}, {month}, {year}. See under {Clock},
      {Day}, etc.

   {Sideral time}, time as reckoned by sideral days, or, taking
      the sidereal day as the unit, the time elapsed since a
      transit of the vernal equinox, reckoned in parts of a
      sidereal day. This is, strictly, apparent sidereal time,
      mean sidereal time being reckoned from the transit, not of
      the true, but of the mean, equinoctial point.
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Clock \Clock\ (kl[o^]k), n. [AS. clucge bell; akin to D. klok
   clock, bell, G. glocke, Dan. klokke, Sw. klocka, Icel. klukka
   bell, LL. clocca, cloca (whence F. cloche); al perh. of
   Celtic origin; cf. Ir. & Gael. clog bell, clock, W. cloch
   bell. Cf. {Cloak}.]
   1. A machine for measuring time, indicating the hour and
      other divisions; in ordinary mechanical clocks for
      domestic or office use the time is indicated on a
      typically circular face or dial plate containing two
      hands, pointing to numbers engraved on the periphery of
      the face, thus showing the hours and minutes. The works of
      a mechanical clock are moved by a weight or a spring, and
      it is often so constructed as to tell the hour by the
      stroke of a hammer on a bell. In electrical or electronic
      clocks, the time may be indicated, as on a mechanical
      clock, by hands, but may also be indicated by direct
      digital readout, with the hours and minutes in normal
      Arabic numerals. The readout using hands is often called
      analog to distinguish it from the digital readout. Some
      clocks also indicate the seconds. Clocks are not adapted,
      like the watch, to be carried on the person. Specialized
      clocks, such as {atomic clocks}, may be constructed on
      different principles, and may have a very high precision
      for use in scientific observations.
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   2. A watch, esp. one that strikes. [Obs.] --Walton.
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   3. The striking of a clock. [Obs.] --Dryden.
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   4. A figure or figured work on the ankle or side of a
      stocking. --Swift.
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   Note: The phrases what o'clock? it is nine o'clock, etc., are
         contracted from what of the clock? it is nine of the
         clock, etc.
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   {Alarm clock}. See under {Alarm}.

   {Astronomical clock}.
      (a) A clock of superior construction, with a compensating
          pendulum, etc., to measure time with great accuracy,
          for use in astronomical observatories; -- called a
          regulator when used by watchmakers as a standard for
          regulating timepieces.
      (b) A clock with mechanism for indicating certain
          astronomical phenomena, as the phases of the moon,
          position of the sun in the ecliptic, equation of time,
          etc.

   {Electric clock}.
      (a) A clock moved or regulated by electricity or
          electro-magnetism.
      (b) A clock connected with an electro-magnetic recording
          apparatus.

   {Ship's clock} (Naut.), a clock arranged to strike from one
      to eight strokes, at half hourly intervals, marking the
      divisions of the ship's watches.

   {Sidereal clock}, an astronomical clock regulated to keep
      sidereal time.
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