Harvest Watercooler

The leap second was introduced in 1972. It was added to keep our modern timekeepers - atomic clocks, which rely on the vibrations in atoms to provide a very accurate measurement of time - in line with our slightly less reliable timekeeper, the Earth.

Because our planet wobbles a little on its axis as it spins, it means some days end up being a few milliseconds longer or shorter than others.This means that over time, the time based on atomic clocks, and the time based on the Earth’s rotation drift further and further apart.

When this difference is deemed by the International Earth Rotation Service, which monitors the Earth’s activity, to be approximately 0.9 seconds, a leap second is added to pull the two back into sync.