A day on Earth is slowly stretching longer, useful context for a colleague or friend curious about how the Moon and climate shape our planet’s rhythm.
Earth’s days are getting longer Story flow and key facts
Earth's rotation is gradually slowing, making days longer over millions of years. The primary force behind this shift is tidal friction caused by the Moon’s gravitational pull on Earth’s oceans. Because Earth spins faster than the Moon orbits, tidal bulges lead the Moon’s position, creating drag that slows Earth’s rotation while pushing the Moon further away by about 3.8 centimeters per year.
Scientists estimate that each century, a day lengthens by 1.7 to 2 milliseconds. While imperceptible in human timescales, this adds up: 100 million years ago, a day lasted about 23 hours, and 1.4 billion years ago, it may have been as short as 18 hours. Additional factors like melting glaciers, rising sea levels, and shifts in Earth’s core also influence rotation speed.
The change is not just academic — precise systems like GPS and internet networks rely on exact timekeeping. To keep atomic clocks aligned with Earth’s rotation, leap seconds have occasionally been added. Climate change is now contributing measurably to rotational shifts, making this a subtle but growing intersection of astronomy and environmental science.
Facts
- Earth’s rotation is slowing by about 1.7 to 2 milliseconds per century.
- The Moon is drifting away from Earth by approximately 3.8 centimeters per year due to tidal friction.
- Around 1.4 billion years ago, a day on Earth was about 18 hours long.
- Melting glaciers and climate change are now measurably affecting Earth’s rotation speed.
- Leap seconds have been added to atomic time to keep global systems synchronized with Earth’s rotation.
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