The last leap second, so far

At the end of 2016 the world's clocks were told to read 23:59:60 for one second, for the twenty-seventh and, so far, final time.

Leap seconds exist because the Moon is slowing the Earth down: tidal friction stretches the day by about 1.7 milliseconds a century, so a day defined by atomic clocks drifts away from a day defined by the sky. In 2022 the international weights and measures conference voted to stop adding them by 2035 and let the discrepancy run.