International timekeepers replace leap second with leap hour to reduce system risks

Leap Second Replaced

The world's official timekeepers have voted to replace the leap second with a leap hour. This decision was made by delegates from 69 countries at a conference of the International Bureau of Weights and Measures in France. The change is set to take effect next year.

Addressing System Risks

The primary motivation for adopting the leap hour is to reduce the risk of computer systems and other technical infrastructure encountering issues. Current software struggles with minutes that occasionally last 61 or 59 seconds due to the leap second. The leap hour aims to eliminate these irregular minute lengths.

Dr. Setnam Shemar, principal scientist at the UK's National Physical Laboratory, stated that this change will reduce risks to systems and national infrastructure dependent on accurate time, while maintaining the link between global time and Earth's rotation.

Impact on Coordinated Universal Time (UTC)

The vote means that Coordinated Universal Time (UTC) can now drift by up to an hour from astronomical time before a leap hour correction becomes necessary. This is not expected to occur for thousands of years. Shemar noted that hourly changes are already common with daylight saving, which does not cause significant disruption.

Background of Timekeeping

The more familiar leap year, introduced over 2,000 years ago, ensures the calendar aligns with Earth's orbit around the sun by adding a day every four years. Leap seconds are a more recent invention, stemming from the development of the caesium atomic clock in 1955 by Louis Essen and Jack Parry at the NPL.

In 1967, the astronomical definition of a second was replaced by a formal definition based on the vibrations of the caesium atom. Atomic clocks are crucial for modern computer systems, communications, satellites, trading systems, and electricity grids due to their stability and precision.