CGPM decides to end leap seconds

The General Conference on Weights and Measures (CGPM) has voted to stop using leap seconds, which are extra seconds added to keep atomic time aligned with solar time. The change will take effect on May 20, 2027, after which the gap between atomic and solar time will grow, potentially reaching an hour over millennia.

Leap seconds and their purpose

A leap second is an additional second occasionally inserted into the clock to account for the Earth's irregular rotation. This ensures that Coordinated Universal Time (UTC), based on atomic clocks, remains close to solar time, which is determined by the position of the Sun in the sky.

History of time measurement

The concept of a second originally came from observing the Sun's movement. Ancient civilizations, like the Egyptians and Babylonians, divided the day into smaller units, laying the foundation for modern timekeeping. Mechanical clocks in the Middle Ages improved accuracy, allowing for the division of time into hours, minutes, and seconds.

Evolution of the second's definition

The second was first officially defined in 1889 as a fraction of the mean solar day. However, this was later replaced by a more precise definition based on the Earth's orbit around the Sun in 1960. By 1967, the second was redefined using the frequency of radiation from a cesium 133 atom, providing a much more stable and accurate measure of time.

Challenges with leap seconds

Atomic time is perfectly regular, but solar time changes due to the Earth's variable rotation speed. To address this, leap seconds were introduced in 1972. However, over time, concerns about technical issues and software complications led to growing opposition to the practice.