New research confirms that tidal interactions between Earth and the Moon are gradually transferring rotational energy from our planet to its satellite. This process causes the Moon to recede from Earth at an average rate of 3.8 centimeters per year, while simultaneously slowing Earth's rotation and lengthening our days.
Scientists have measured this effect using lunar laser ranging experiments, which bounce laser beams off reflectors placed on the Moon during the Apollo missions. These precise measurements show that the Moon's orbit is expanding, and Earth's day length is increasing by about 1.8 milliseconds per century.
The phenomenon is a natural consequence of gravitational tidal forces. The Moon's gravity raises tides on Earth, and the friction of these tides dissipates energy, causing the Moon to gain orbital energy and drift outward. This process has been ongoing for billions of years and will continue far into the future.
While the daily change is imperceptible, the cumulative effect is significant over geological timescales. For example, 620 million years ago, Earth's day was only about 21.9 hours long, and there were about 400 days per year.
