Some minutes have 61 seconds
Since 1972, UTC has occasionally inserted a leap second, so that 23:59:60 is a real timestamp and noon stays near the Sun.
The second is a number of oscillations of caesium, which this library already records. The day is a turn of the Earth, which wanders: tides, ice sheets, and the fluid core push the length of the day around by milliseconds. UTC follows atomic time and, when the difference from the Earth's angle approaches 0.9 seconds, a leap second is inserted or, in principle, removed.
Twenty-seven leap seconds were inserted between 1972 and 2016. None has been inserted since, because the Earth has been running a little fast. A negative leap second has never been needed. In 2022 the General Conference on Weights and Measures resolved to stop the practice by 2035. The 61-second minute is real, documented, and scheduled for retirement.
Caveats
- Leap seconds are irregular. Most minutes, including most New Year's Eves, have 60 seconds.
- The abolition is a decision about coordination, not a discovery that the Earth has become uniform.
Sources
- 1Nelson R. A. et al.. The leap second: its history and possible future. Metrologia 38, 2001.