Once upon a time, a leap-second …..

Leap seconds were invented in 1972 (in which year we had 2 leap seconds, one in June and one in December). In 26 of the 44 years since 1972 we have had leap seconds. A year with a leap second happens more often than a year without. Today we add the 27th leap second since its introduction.

A leap second is a one-second adjustment that is occasionally applied to Coordinated Universal Time (UTC) in order to keep its time of day close to the mean solar time, or UT1. Without such a correction, time reckoned by Earth’s rotation drifts away from atomic time because of irregularities in the Earth’s rate of rotation. Since this system of correction was implemented in 1972, 26 leap seconds have been inserted, the most recent on June 30, 2015 at 23:59:60 UTC, and the next leap second will be inserted on December 31, 2016, at 23:59:60 UTC.

Having a leap-second is the new normal.

Deviation of day length from SI based day – Wikipedia



One Response to “Once upon a time, a leap-second …..”

  1. thesciencegeek Says:

    Great post !

    On the subject of leap second I posted a similar account at:


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