Leap second: when will it be where you live?

Everyone gets the extra moment simultaneously — so it will happen at different times depending on where you are

The Union Flag flutters in front of the Big Ben clock tower on the Houses of Parliament in London

The world is set to get an extra second on Tuesday night — but when exactly that happens will depend on where you are.

Authorities are set to make the last minute of the hour one second longer, meaning that clocks will count up to 60 rather than 59 before switching over. But because it happens simultaneously around the world, the exact time that it happens which timezone you are in.

The change happens at 23.59 co-ordinated universal time, or UTC. UTC is practically the same as GMT — so you can work out the time the leap second will happen according to how many hours behind or ahead of that you are.

The UK is an hour ahead at the moment because it’s on British Summer Time, for instance, which means that the leap second will happen at 00.59am on Wednesday morning.

West of the UK it is earlier, so the change will happen on Tuesday afternoon or evening. And east of the UK is later, so it will happen on Wednesday morning.

Some have worried that the leap second could bring chaos for computers, as it has in the past. Though engineers have tried to ensure that computers can deal with the issues, there's very little that normal people can do.