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. [ 1913 Webster ] 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. [ 1913 Webster ] Ere twice the horses of the sun shall bring
Their fiery torcher his diurnal ring. Shak. [ 1913 Webster ] 3. (Bot.) Opening during the day, and closing at night; -- said of flowers or leaves. [ 1913 Webster ] 4. (Zool.) Active by day; -- applied especially to the eagles and hawks among raptorial birds, and to butterflies (Diurna) among insects. [ 1913 Webster ]
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. [ 1913 Webster ] | 
