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:
“That’s one small step for a man, one giant leap for mankind.”
—Neil Armstrong (b. 1930)
“You have known your friend so long and loved him so much, and then all of a sudden you are so mad at him, you say, I could just kill you and you still like each other, because you have always been friends and you know in your mind you are going to be friends in a few seconds anyway.”
—Anonymous Twelve-Year-Old. As quoted in Children’s Friendships by Zick Rubin, ch. 3 (1980)