Moon Recedes 3.8 Centimetres a Year as Earth’s Day Lengthens by Milliseconds
Updated
Updated · spacedaily.com · May 31
Moon Recedes 3.8 Centimetres a Year as Earth’s Day Lengthens by Milliseconds
2 articles · Updated · spacedaily.com · May 31
Summary
Laser ranging off Apollo and Soviet reflectors shows the Moon is moving away from Earth by about 3.8 centimetres a year, while Earth’s day is lengthening by a couple of milliseconds per century.
Tidal bulges raised by the Moon are dragged ahead by Earth’s faster rotation, and that gravitational mismatch transfers Angular momentum from Earth’s spin into the Moon’s orbit rather than “stealing” time.
Around 4.5 billion years ago, Earth’s day was likely 10 hours or less, not 19 hours; the 19-hour figure marks a later stage, not the starting point.
A 2023 Nature Geoscience study suggests the day then stalled near 19 hours for roughly 1 billion years, between about 2 billion and 1 billion years ago, as lunar ocean tides and solar-driven atmospheric tides nearly canceled out.
Today’s 3.8-centimetre recession rate cannot be projected straight backward, because tidal braking changes with ocean basins and continents, and the modern Atlantic likely makes the current slowdown unusually strong.