A Day is Not Exactly 24 Hours Long

If you have ever lived in a daylight savings area, you probably rejoice for that extra hour in bed, or maybe wince when it is taken away. However, you may have completely missed the fact that over the last 30 years you’ve also been granted an extra 15 seconds without any subsequent reversal.

This effect is a result of the “leap second,” a one-second adjustment that is occasionally made to compensate for the minor changes in the earth’s rotation. In theory, a negative leap second could occur, but it has yet to do so. 15 leap seconds have been made since 1980 and although it isn’t yet known when the next one will occur, historically they take place, on average, every 18 months.


Wikipedia: Leap Second

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One Response to A Day is Not Exactly 24 Hours Long

  1. Steve Allen says:

    No, a day is always 24 hours long, because an hour is 1/24th of a day.
    3600 seconds of TAI is not a unit specified by the BIPM, and not an hour.
    the two are measuring different things

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