The Moon is currently receding from Earth at a rate of approximately 3.8 centimeters (1.5 inches) per year. This is roughly the same rate at which human fingernails grow. This recession is caused by a complex gravitational interaction between Earth and the Moon.

The Mechanics of Lunar Recession

The Moon's gradual retreat from Earth is primarily driven by tidal forces. The Moon's gravitational pull creates tidal bulges in Earth's oceans, while Earth's gravity causes similar tidal effects on the Moon, giving it a slightly football-like shape. As Earth rotates faster than the Moon orbits, these tidal bulges move slightly ahead of the Moon in its orbit. This creates a gravitational interaction whereby:

• The tidal bulge pulls forward on the Moon, accelerating it and pushing it into a higher orbit
  
• Simultaneously, the Moon's gravity pulls backward on the bulge, slowing Earth's rotation

This transfer of angular momentum from Earth to the Moon is the fundamental mechanism behind lunar recession. As Earth's rotation slows down, the Moon gains that energy as angular momentum, causing it to move into a higher orbit around our planet.

Historical Variations in Recession Rate

The current recession rate of 3.8 cm per year is actually unusually high compared to the average rate throughout Earth's history. If the Moon had been receding at this current rate for its entire 4.5-billion-year existence, it would have had to start much closer to Earth than scientific evidence suggests.

Research indicates that:

• Around 3.2 billion years ago, the Moon was approximately 270,000 km from Earth (about 70% of its current distance)
• During the period 550-625 million years ago, the Moon may have been receding at a faster rate of up to 7 cm (2.8 inches) per year
• 
  The recession rate has varied significantly over time, influenced by factors such as the configuration of Earth's continents and oceans

Scientists have determined these historical recession rates by studying ancient rock formations that preserve evidence of Milankovitch cycles, which are affected by the Earth-Moon distance. For example, analysis of banded iron formations in Australia from 2.46 billion years ago suggests the Moon was about 60,000 kilometers closer to Earth at that time.

Future Projections

The lunar recession will continue into the future but at a gradually decreasing rate. Models predict that:

In about 50 billion years, Earth's slowing rotation would cause it to become tidally locked with the Moon, at which point they would stop moving away from each other

• However, in approximately 5 billion years, the Sun will enter its red giant phase, likely disrupting and destroying the Earth-Moon system before tidal locking can occur

If the Moon continued receding at its current rate until the Sun's red giant phase, it would move an additional 117,000 miles (189,000 km) away from Earth
This ongoing recession has measurable effects on Earth, including a gradual lengthening of our day by approximately 1.09 to 1.78 milliseconds per century.