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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Aberration \Ab`er*ra"tion\, n. [L. aberratio: cf. F. aberration.
   See Aberrate.]
   1. The act of wandering; deviation, especially from truth or
      moral rectitude, from the natural state, or from a type.
      "The aberration of youth." --Hall. "Aberrations from
      theory." --Burke.
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   2. A partial alienation of reason. "Occasional aberrations of
      intellect." --Lingard.
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            Whims, which at first are the aberrations of a
            single brain, pass with heat into epidemic form.
                                                  --I. Taylor.
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   3. (Astron.) A small periodical change of position in the
      stars and other heavenly bodies, due to the combined
      effect of the motion of light and the motion of the
      observer; called annual aberration, when the observer's
      motion is that of the earth in its orbit, and daily or
      diurnal aberration, when of the earth on its axis;
      amounting when greatest, in the former case, to 20.4'',
      and in the latter, to 0.3''. Planetary aberration is
      that due to the motion of light and the motion of the
      planet relative to the earth.
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   4. (Opt.) The convergence to different foci, by a lens or
      mirror, of rays of light emanating from one and the same
      point, or the deviation of such rays from a single focus;
      called spherical aberration, when due to the spherical
      form of the lens or mirror, such form giving different
      foci for central and marginal rays; and chromatic
      aberration, when due to different refrangibilities of the
      colored rays of the spectrum, those of each color having a
      distinct focus.
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   5. (Physiol.) The passage of blood or other fluid into parts
      not appropriate for it.
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   6. (Law) The producing of an unintended effect by the
      glancing of an instrument, as when a shot intended for A
      glances and strikes B.
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   Syn: Insanity; lunacy; madness; derangement; alienation;
        mania; dementia; hallucination; illusion; delusion. See
        Insanity.
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