TIME will stand still in South East Cornwall – and all over the world – as an extra second is added to the day on June 30.

The 'leap second' will be added at midnight to allow for the fact that the Earth's speed of rotation is not quite as predictable and 'accurate' as the atomic time measurements used by its inhabitants since the 1960s.

At Liskeard School and Community College, science teacher Mike Willmott will be building lessons around the Earth's movement, and the human concepts of time.

'We human beings like things to work in a nice, simple, regular way – but the way the Earth moves isn't like that,' he said.

'The Earth's rate of spin changes slightly, and this can be due to huge tidal surges, or convection currents deep in the planet's mantle.'

These slight changes in speed are not predictable, says Mr Willmott, so every six months, scientists at the International Earth Rotation Service in France have to decide whether a leap second needs to be added – or taken away.

Those wanting to see evidence of the leap second on Tuesday night should try to watch an atomic clock, which will show the rare reading 23:59:60.