Scientists say Saturday will stretch a second longer than any other day this year.

A team at the Paris Observatory is adding a "leap second" just before midnight to make up for a gradual slowdown in the Earth's rotation.

Experts at the International Earth Rotation and Reference System Service make the adjustment when the planet's movement falls out of sync with atomic clocks used to measure time.

A second can be added or removed as needed every six months, but it typically happens only every 1.5 years.

This week's change comes after nearly four years without a leap second — the last one was at the end of December 2008.

Twenty-four extra seconds have been introduced since the process started in 1972.

There are normally 86,400 seconds in a day.

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