Scientists have confirmed that the Moon is gradually drifting away from Earth at a rate of 1.5 inches (3.8cm) per year, a process known as 'lunar recession'. This movement is causing Earth's days to lengthen over geological timescales, with the average day increasing by about 1.09 milliseconds per century since the late 1600s.
The phenomenon is driven by tidal interactions between the Earth and Moon. As the Earth rotates, the Moon's gravity pulls on the oceans, creating tidal bulges. Because Earth spins faster than the Moon orbits, friction drags these bulges slightly ahead of the Moon, which then pulls them back, slowing Earth's rotation and transferring angular momentum to the Moon, pushing it into a higher orbit.
Professor David Waltham of Royal Holloway, University of London, explains: 'It's all about tides. The tidal drag on the Earth slows its rotation down and the Moon gains that energy as angular momentum.' Measurements using lasers fired at reflectors left on the Moon by Apollo missions have provided precise data on the recession rate.
Over billions of years, the effect has been significant. Around 3.2 billion years ago, the Moon was about 270,000km (170,000 miles) from Earth, compared to its current distance of 384,400km (238,855 miles). Early Earth days lasted less than 13 hours, and the gradual lengthening continues.
Climate change may also be playing a role. Melting polar ice caps and glaciers are increasing the size of Earth's oceanic bulge, further slowing the planet's spin. This has implications for timekeeping, as leap seconds are occasionally added to synchronise atomic clocks with Earth's rotation. Geoscientist David Agnew of the University of California, San Diego, notes that a leap second may need to be removed in coming years due to recent accelerated rotation—an unprecedented event.
