The Moon is drifting away

0:00 The Moon is slowly leaving us,

0:01 drifting about four centimetres farther from

0:04 Earth every year —

0:05 roughly the speed your fingernails grow.

0:08 The cause is the tides.

0:09 The Moon's gravity pulls the oceans into

0:12 bulges,

0:12 but Earth spins faster than the Moon orbits,

0:15 so those bulges are dragged slightly ahead.

0:18 Their gravity tugs the Moon forward,

0:20 nudging it into a wider orbit.

0:22 In exchange, Earth's spin gradually slows,

0:25 making our days a tiny bit longer over

0:27 millions of years.

0:28 Long ago, a day lasted only eighteen hours.