Effect of the Moon
The Moon is moving away
Established
About 3.8 cm a year, measured by laser.
The evidence
Laser pulses fired at the reflectors left by Apollo measure the Earth–Moon distance. From 20 138 ranges between 1970 and 2015, the Moon recedes by 38.30 ± 0.09 mm a year. Tides slow Earth’s spin and hand that momentum to the Moon’s orbit.
Key studies
- Lunar Laser Ranging: A Continuing Legacy of the Apollo Program Showed how laser ranging measures the Moon’s tidal acceleration, and so its slow escape.
- Secular tidal changes in lunar orbit and Earth rotation The source of the modern recession rate, 38.30 ± 0.09 mm a year.
- On the relation of the lunar recession and the length-of-the-day Sums up the laser data (20 138 ranges, 1970–2015) and argues the two rates still do not fully agree.