What Should You Do With Your Extra Second?
On June 30, 2015, the day will be a second longer than normal. Make the most of it!
A leap second will be added to clocks on June 30.
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We have to add a leap second every now and again in order to synchronise atomic clocks with astronomical time. That's because Earth's rotation is slowing down. Don't worry though, it's happening verrrrrrrrrrry slooooooowwwwly – we've only had to add 25 leap seconds since 1974.
They work the same way as the extra day does in a leap year. This next one will be the 26th leap second, and it gets added at 23:59:60 UTC.