Tuesday will be a bit longer than other days because an extra second, or ‘leap’ second, will be added to the day, reports The Hindu.

“Earth’s rotation is gradually slowing down a bit, so leap seconds are a way to account for that,” said Daniel MacMillan of Nasa’s Goddard Space Flight Centre.

Strictly speaking, a day lasts 86,400 seconds, going by the Coordinated Universal Time, or UTC. UTC is “atomic time” — the duration of one second is based on extremely predictable electromagnetic transitions in the atoms of cesium.

These transitions are so reliable that the cesium clock is accurate to one second in 1,400,000 years.

However, the average length of a day is about 86,400.002 seconds long. That’s because Earth’s rotation is gradually slowing down a bit.

This difference of two milliseconds, or two thousandths of a second — far less than the blink of an eye — hardly seems noticeable at first. But it can add up over time.