diurnal arc

Diurnal \Di*ur"nal\, a. [L. diurnalis, fr. dies day. See
   {Deity}, and cf. {Journal}.]
   1. Relating to the daytime; belonging to the period of
      daylight, distinguished from the night; -- opposed to
      {nocturnal}; as, diurnal heat; diurnal hours.
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   2. Daily; recurring every day; performed in a day; going
      through its changes in a day; constituting the measure of
      a day; as, a diurnal fever; a diurnal task; diurnal
      aberration, or diurnal parallax; the diurnal revolution of
      the earth.
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            Ere twice the horses of the sun shall bring
            Their fiery torcher his diurnal ring. --Shak.
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   3. (Bot.) Opening during the day, and closing at night; --
      said of flowers or leaves.
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   4. (Zool.) Active by day; -- applied especially to the eagles
      and hawks among raptorial birds, and to butterflies
      (Diurna) among insects.
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   {Diurnal aberration} (Anat.), the aberration of light arising
      from the effect of the earth's rotation upon the apparent
      direction of motion of light.

   {Diurnal arc}, the arc described by the sun during the
      daytime or while above the horizon; hence, the arc
      described by the moon or a star from rising to setting.

   {Diurnal circle}, the apparent circle described by a
      celestial body in consequence of the earth's rotation.

   {Diurnal motion of the earth}, the motion of the earth upon
      its axis which is described in twenty-four hours.

   {Diurnal motion of a heavenly body}, that apparent motion of
      the heavenly body which is due to the earth's diurnal
      motion.

   {Diurnal parallax}. See under {Parallax}.

   {Diurnal revolution of a planet}, the motion of the planet
      upon its own axis which constitutes one complete
      revolution.

   Syn: See {Daily}.
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