Why June 30 Will Be 1 Second Longer?
2015 is not a leap year, but it does have a leap second, set to take place Tuesday (June 30) at 7:59:60 p.m. EDT (23:59:60 GMT).
"Earth's rotation is gradually slowing down a bit, so leap seconds are a way to account for that," Daniel MacMillan of NASA's Goddard Space Flight Center in Greenbelt, Maryland, said in a statement.
Ask any person the length of a day, and she'll say 24 hours, which equates to 86,400 seconds. But the time it takes for Earth to rotate on its axis relative to the sun, called a mean solar day (or the average length of a day) is roughly 86,400.002 seconds. This happens because Earth's rotation is slowing down, thanks to a kind of braking force caused by the gravitational tug of war among Earth, the sun and the moon, researchers at NASA said.
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