Last updated at 08:16

Why do we have leap seconds?

Girl with a clockGetty Images

As you know, usually a minute lasts for 60 seconds.

But every now and then, one minute can actually last for 61 seconds.

This is called a leap second, and we've used them since 1972, to help make sure the time on our watches matches how the Earth is rotating.

The latest leap second came at the very end of 2016. The year was in fact a second longer than you might have expected, with one extra second added to the minute from 11:59pm to 12:00am on New Year's Eve.

Computer illustration of the EarthScience Photo Library
We add a second to our clocks sometimes to make sure that they match with the way the Earth is rotating

Leap seconds are added either at the end of June or at the end of December.

You might remember that in June 2015, Newsround reported that an extra second was being added to the time. The last leap second before that was in 2012.

They occur at irregular intervals like this as the Earth's rotation isn't completely predictable! And we only find out when they're going to happen six months in advance.

Big Ben on New Year's Eve
An extra second was added to 2016 just before the midnight fireworks on New Year's Eve

The 2016 leap second is our 28th leap second since we started having them.

For ideas about what you could do with your extra second, check out Newsround's top tips!