Leap Seconds
To keep the civil day aligned with the apparent movement of the Sun, positive or negative leap seconds may be inserted.
A civil clock day is typically 86,400 SI seconds long, but will be 86,401 s or 86,399 s long in the event of a leap second.
Leap seconds are announced in advance by the International Earth Rotation and Reference Systems Service which measures the Earth's rotation and determines whether a leap second is necessary. Leap seconds occur only at the end of a UTC month, and have only ever been inserted at the end of June 30 or December 31.
Read more about this topic: Day
Famous quotes containing the words leap and/or seconds:
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—Clifton Fadiman (b. 1904)
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—Aldous Huxley (1894–1963)