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THE LEAP SECOND, EXPLAINED

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WHY DO WE ADD ONE SECOND TO THIS DAY, AND DOES IT MATTER AT ALL?

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Today, Earth's official time as measured by atomic clocks will have one extra "leap" second. What explains this tiny addition? We explain.

Why do we need the leap second?

While we believe the Earth's rotation on its axis to be regular, it isn't - the rotation's actually slowing down, very gradually, due to competing gravitational forces between the Earth, Sun, and Moon. Rather than calculate the actual rotation time every day, scientists pick certain points to add on an additional second to make up the difference. Simply put: the experts review the data and decide when to put a little bit more time on our collective clock.

When is the leap second added?

To the very end of the day; June 30, 23:59:59 jumps to 23:59:60 instead of the beginning of July 1.

Are there any negative consequences to the leap second?

Generally, no. Most of us don't even notice that the day's been slightly extended, and, if we do, one second isn't enough time for much to change. Some computer systems, however, encounter major glitches because their code isn't equipped to handle this irregularity. The last time we added a leap second, it caused several websites to crash.

Should I be concerned?

Nah, you'll probably be fine. It's just one teensy second!