Scientists Move Toward a New Way to Keep Official Time

Scientists have voted to change how the world keeps official time, although most people are unlikely to notice the difference. The decision concerns the small gap between highly precise clocks and the Earth's natural rotation.

A full turn of the Earth is often described as 24 hours. In reality, the planet's spin changes slightly, and it has slowed down by a very small amount. As a result, one rotation can take 24 hours plus a number of microseconds, or millionths of a second.

Since 1972, timekeepers have used leap seconds to deal with this difference. A leap second is an extra second added to official time when necessary. However, member states at the General Conference on Weights and Measures, which recently met in Versailles near Paris, decided to abandon that system. They introduced the concept of a leap hour, allowing much more time to pass before an adjustment is made.

Philippe Richard, director of Switzerland's Federal Institute of Metrology, explained the idea in an interview with NPR host Scott Simon. He compared the situation with two watches: an old mechanical watch representing the Earth and a very precise quartz watch representing modern timekeeping. If the two watches gradually move apart, one must be corrected to follow the other.

The difference may seem too small to matter in daily life. Yet precise time is important for scientific measurement and technical systems. A longer adjustment period could make those systems easier to manage, while ordinary activities such as checking a clock or arranging a meeting should remain unchanged. The decision shows how scientists continue to adapt measurement standards to the natural world.