Eventually, days could become 25 hours long as Moon moves farther away from Earth
In this DML Report…
The Moon is receding from Earth at a rate of 1.5 inches (3.8 cm) per year, a process driven by tidal interactions that has been ongoing since the Moon formed approximately 4.5 billion years ago. This gradual drift results from gravitational forces creating ocean bulges on Earth, which are pulled slightly ahead of the Moon's position due to Earth's faster rotation; the friction from these tides transfers angular momentum to the Moon, expanding its orbit. Currently, the average distance between Earth and the Moon stands at 239,000 miles (384,000 km), with the annual increase representing just 0.00000001 percent of that distance. Measurements confirming this rate come from laser ranging experiments, where lasers are fired at reflectors placed on the lunar surface by Apollo missions, allowing precise tracking of the Moon's position over time.
This recession has measurable effects on Earth's rotation, slowing it down through tidal friction and thereby lengthening the day. Historical data indicates that about 70 million years ago, during the late dinosaur era, days lasted only 23.5 hours due to the Moon's closer proximity at that time. Over human timescales, the change remains imperceptible, but projections suggest days could eventually extend to 25 hours. The process also influences tides, as the Moon's gravitational pull diminishes with distance, potentially weakening tidal forces in the distant future. In approximately one billion years, the Sun's increasing brightness is expected to evaporate Earth's oceans, halting tidal activity and thus the recession.
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Long-term implications include the eventual tidal locking of Earth and the Moon, where both bodies would always show the same face to each other, occurring tens of billions of years from now if not interrupted by solar evolution. Total solar eclipses, which rely on the Moon's apparent size matching the Sun's due to its current distance, will continue for millions of years despite the drift, as the change is minimal over short geological periods. However, in a few billion years, the Sun's expansion into a red giant will likely engulf or destroy both Earth and the Moon. As noted by Dr. Stephen DiKerby, a researcher in Physics and Astronomy at Michigan State University, these effects are so gradual that "We'll keep having eclipses, tides and days that last 24 hours for millions of years."