50 years ago, timekeepers deployed the newly invented leap second

Excerpt from the January 12, 1974 issue of Science News

A hand holds a stop watch

The leap second’s time is nearly up. Scientists will retire the tool used to reset atomic clocks by 2035.

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cover of the January 12, 1974 issue of Science News

Happy leap second!Science News, January 12, 1974

A “leap second” has been invented … to keep time signals used by navigators in step with the actual motion of the Earth. The latest leap second was celebrated New Year’s Eve at the stroke of midnight Greenwich Mean Time, when around the world … radio stations added an extra “beep” to their hourly time signals.


Time is running out for the leap second. In 2022, metrologists voted to abandon the timekeeping quirk by 2035. Unlike the leap year, which occurs every four years, the leap second is deployed whenever clocks need adjusting due to variations in Earth’s spin causing slight changes in the length of a day. Global officials have inserted a leap second 27 times since 1972. But satellites and other tech that rely on the precise time kept by atomic clocks can glitch when the clocks are adjusted (SN: 4/22/06, p. 248). Scientists have suggested using a leap minute instead, which would require atomic clocks be reset once every 50 years or so.

Cassie Martin is a deputy managing editor. She has a bachelor's degree in molecular genetics from Michigan State University and a master's degree in science journalism from Boston University.

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