Leap Second
A one-second adjustment occasionally added to UTC to accommodate irregularities in Earth's rotation.
A leap second is a one-second adjustment that is occasionally added to Coordinated Universal Time (UTC) to accommodate the irregular rotation of the Earth. Unlike leap years, which follow a regular pattern, leap seconds are inserted irregularly based on astronomical observations.
The Earth's rotation is gradually slowing due to tidal friction, making the mean solar day slightly longer than 86,400 seconds. To keep UTC within 0.9 seconds of UT1 (time based on Earth's rotation), leap seconds are added when necessary.
Since their introduction in 1972, leap seconds have typically been added at a rate of about one every 18 months. They are usually scheduled for June 30 or December 31.
Leap seconds pose challenges for computer systems, which often aren't designed to handle a 61-second minute. Due to these complications, there have been proposals to eliminate leap seconds.