Leap seconds and their impact

Leap seconds are extra seconds added to clocks to keep them in sync with Earth's rotation. These seconds are used to correct for the irregular slowing of Earth's rotation, which causes a gradual drift between atomic time and the time based on Earth's rotation.

History of the second

The concept of the second dates back to ancient times, when the day was divided into 24 hours, each hour into 60 minutes, and each minute into 60 seconds. This base-60 system was used by the Sumerians and Babylonians and is still in use today.

Modern definition of the second

In 1967, the General Conference on Weights and Measures defined the second based on the cesium-133 atom, which emits radiation that oscillates at a highly stable rhythm. This definition is used in Coordinated Universal Time (UTC), which relies on atomic clocks.

Leap seconds and their use

Since 1972, 27 leap seconds have been added to UTC to keep the difference between UTC and UT1, the time scale based on Earth's rotation, below 0.9 seconds. The last leap second was added at the end of 2016.

Challenges with leap seconds

Adding a leap second can disrupt computer systems that assume a day lasts 86,400 seconds. In 2012, Reddit experienced an outage after a leap second was added. Major technology companies use a technique called "smearing" to gradually distribute the extra second over a long period.

Changes in Earth's rotation

Since around 2015, Earth has been rotating faster than usual. In 2020, 28 days were recorded where Earth completed a full rotation in less than 86,400 atomic seconds. The shortest day measured since atomic clocks were introduced was on June 29, 2022.

Future of leap seconds

The General Conference on Weights and Measures may decide to increase the allowable difference between UTC and UT1 by 2035. A draft resolution could make UTC a continuous time scale, allowing a one-hour difference between UTC and UT1 over several centuries.

Implications for timekeeping

The change would not be noticeable in daily life, as most electronic devices do not display seconds. However, astronomers and Earth scientists will need to account for the growing drift between UTC and UT1 in their observations and measurements. Monitoring these time scales will become increasingly important for high-precision time measurement.