Our current system of civil time is based on coordinated universal time (UTC), which is based on a system of atomic clocks. Leap seconds are used to guarantee that UTC does not differ from the Earth's rotational time by more than 0.9 seconds. The Earth's rotation is decelerating at a rate of about 1.5 to 2 milliseconds per day per century due to the frictional action of the tides. Currently, the Earth is slower than UTC by about 2 milliseconds per day, so every 450 to 500 days the time difference reaches 0.9 seconds. Leap seconds are added to UTC to keep the two times in agreement.
Interesting questions arise:
How long will it take until...
- we need a yearly, monthly or daily leap second?
- we need a leap second per second?
- we need a leap day per second?
- Earths rotation will finally stop? Within our Sunīs lifetime?
(Update: Spelling enhancements)