The earth rotates once in about 24 hours with respect to the Sun. Scientists have discovered that 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. Today, atomic clocks show that a modern-day is longer by about 1.7 milliseconds than a century ago, slowly increasing the rate at which coordinated universal time is adjusted by leap seconds. Historical analysis astronomical records shows a slowing trend of about 2.3 milliseconds per century since the 8th century BCE.