Effect of the Moon
Longer days
Established
Tidal braking lengthens the day, a little.
The evidence
Ancient eclipses show the day growing by 1.8 ms per century since 720 BC. Tides alone would give 2.3 ms; the rebound of land after the ice ages and the core make up the difference. 620 million years ago, a day lasted about 21.9 hours.
Key studies
- Measurement of the Earth's rotation: 720 BC to AD2015 The day lengthens by 1.8 ms per century, less than the 2.3 ms tides alone would give.
- Geological constraints on the Precambrian history of Earth's rotation and the Moon's orbit 620 million years ago a day lasted 21.9 ± 0.4 hours and a year had about 400 of them.