mean day

mean day

The time interval between successive transits of the mean sun at a point on the earth. Because of the elliptical shape of the earth's orbit, the apparent angular velocity of the sun is not constant; hence, the day is indicated by the apparent travel of the mean sun. The length of a mean day is 24 h 3 min 56.555 s. It is divided arbitrarily into twenty-four units known as mean solar hours. Also known as a mean solar day or a civil day.

An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved