01 a. Relating to the daytime; belonging to the period of daylight, distinguished from the night; -- opposed to nocturnal; as, diurnal heat; diur…
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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.“Ere twice the horses of the sun shall bring Their fiery torcher his diurnal ring.” — Shak.
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3.
Opening during the day, and closing at night; -- said of flowers or leaves.(Bot.)
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4.
Active by day; -- applied especially to the eagles and hawks among raptorial birds, and to butterflies (Diurna) among insects.(Zool.)
Phrases & compounds
Diurnal aberration —
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.