time zone

Longitudinal strip of the Earth's surface, stretching from pole to pole and sharing the same time of day or night. In a 24-hour period the Earth makes one complete rotation on its axis; thus the direct rays of the Sun pass through one degree of longitude every 4 minutes. To allow for time changes on an hourly basis, each time zone covers 15 degrees of longitude in width. In practice, however, zone boundary lines are adjusted to accommodate political units. (See also international date line).