Ere twice the horses of the sun shall bring
Their fiery torcher his diurnal ring. Shak.

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.