Clock Watchers Play Catch-Up Tonight

Time will stand still tonight at the U.S. Naval Observatory here--at least for a second.

Right after the Naval Observatory’s official clock strikes 23:59:59 Coordinated Universal Time, or 7:59 and 59 seconds p.m., its red digital numbers will display an improbable 23:59:60, then pick up one second later at 24:00:00. In that “leap second,” the Naval Observatory’s atomic clock will hop into sync with the time kept by the Earth.

Since 1972 scientists have inserted 16 leap seconds in the clock to compensate for slowing of the Earth’s rotation. The leap seconds synchronize the atomic clock, which is accurate to one-billionth of a second per day, with the speed of the Earth’s rotation.