Earth's rotation is slowing slightly with time; thus, a day was shorter in the past. This is due to the tidal effects the Moon has on Earth's rotation. Atomic clocks show that a modern-day is longer by about 1.7 milliseconds than a century ago, slowly increasing the rate at which UTC is adjusted by leap seconds.
Why is Earth's rotation decelerating?
The planet's rotation is slowing down overall because of tidal forces between Earth and the moon. Roughly every 100 years, the day gets about 1.4 milliseconds, or 1.4 thousandths of a second, longer.
What is the deceleration rate of the Earth's rotation?
The average deceleration of Earth's rotation rate from all available fossil data is found to be (5.969 ± 1.762) × 10−7 rad yr−2.
