Chase's Calendar of Events 2014, 57th Edition

Leap Seconds

The information below is developed by the editors from data supplied by the US Naval Observatory.

Because of Earth’s slightly erratic rotation and the need for greater precision in time measurement, it has become necessary to add a “leap second” from time to time to man’s clocks to coordinate them with astronomical time. Rotation of the Earth has been slowing since 1900, making an astronomical second longer than an atomic second. Since 1972, by international agreement, adjustments have been made to keep astronomical and atomic clocks within 0.9 second of each other. The determination to add (or subtract) seconds is made by the Central Bureau of the International Earth Rotation Service, in Paris. Preferred times for adjustment have ...