What's a 'leap second' and a 'leap hour'?

Did you know that on 27 occasions since 1972 an extra second has been added to our clocks to keep our time running smoothly - a bit like a leap year, just much shorter.

It's called a 'leap second' and it's to make sure our clocks keep accurate time.

There's a slight difference between the way we officially measure world time, and the actual speed at which our planet spins, so this extra second helps bridge the gap.

But experts are now deciding whether to get rid of 'leap seconds' altogether and replace them with a 'leap hour' instead.

The decision is due to be made this week - but why does this happen and what difference does it make? Keep reading to find out more .

For thousand of years, humans have used the Sun to help calculate time here on Earth and our system of minutes, hours and days follows the rotation of our planet.

One spin = 24 hours = 1440 minutes = 86400 seconds, right? But that isn't quite as accurate as you might think.

The length of time it takes for the Earth to spin isn't 100% regular, and can actually vary throughout the year.

It's due to lots of factors, including the movement of oceans, the pull of gravity and the molten rock under the Earth's crust.

Our movement through space isn't always smooth and it's totally normal that Earth can sometimes 'wobble' a bit.

These tiny differences mean that the time according to the Earth's position to the Sun, and the time according to our clocks, drifts apart - so scientists have had to come up with ways for us to stay in line.

Since 1972 one way time experts have done this is by adding in a 'leap', or extra, second when they need to.

It's happened 27 times, and the last time was on 31 December 2016 when 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.

Unlike in 1972, in 2026 we live in a world filled with computers, which makes leap seconds increasingly difficult to deal with.

Adding (or removing) seconds into computers' clocks, often with quite short notice, can cause machines to get confused!

For instance when a leap second was added in 2012, a number of big websites were caught out, and crashed.

In Australia, flights were delayed as airport staff were forced to switch to manual check-ins.

Engineers at Meta, who own Instagram, Whatsapp and Facebook have called leap seconds "a major source of pain".

So what's the solution being suggested?

Some experts want to get rid of the leap seconds system altogether, and say we should just let the extra time build up until the Earth's rotation is a full hour out of sync - and then add a 'leap hour instead.

The catch? It could take more than a thousand years until this leap hour is even needed, so 2026 humans would be passing the problem on to the people of the distant future.

Some scientists even argue that technology might have advanced so much by then, that adding extra time wouldn't cause anywhere near as many problems as it does today.

Setnam Shemar, Principal Scientist at the UK's National Physical Laboratory explained: "Leap hours would need to be added very infrequently.

"In fact, it would likely be at least thousands of years before astronomical time and atomic time had drifted apart by close to one hour and a leap hour was needed to be applied."

Setnam went on to suggest that life could be "so different on Earth in thousands of years from now, timekeeping [might not be] at all relevant then."

This week international timekeepers will get together to talk about this issue and vote on what to do.

Hope no-one is late to the meeting!