First Leap Second Added

Date: June 30, 1972 • Location: Rome, Italy

The first leap second is added to the UTC time system.

Leap seconds or intercalary seconds were one-second adjustments occasionally applied to Coordinated Universal Time (UTC) between 1972 and 2016, to accommodate the difference between International Atomic Time (TAI), as measured precisely by atomic clocks, and observed solar time (UT1), which varies due to irregularities and long-term slowdown in the Earth's rotation.