Earth's rotation is slowing, making days longer. The Moon's gravity is the primary driver of this change. Winds, ocean currents, melting ice, and core movements also contribute. Scientists monitor these tiny shifts with precise atomic clocks. This...
By Global Desk |
TIL Creatives
Earth's rotation is slowing, making days longer. The Moon's gravity is the primary driver of this change.
Most of us move through our day assuming one simple fact. A day lasts 24 hours. It feels steady and dependable, like the ground beneath our feet. But in reality, Earth is not a perfect timekeeper. Its rotation shifts ever so slightly, and over long stretches of time, our days are becoming a little longer.
The change is small, measured in milliseconds. Yet in a world powered by GPS, high-speed internet, air travel, and digital banking, even a tiny shift in time can matter.
The Moon Is Slowly Slowing Us Down
The biggest reason Earth’s days are lengthening has to do with the Moon.
The Moon’s gravity pulls on Earth’s oceans, creating tides. Because Earth rotates faster than the Moon circles us, those tidal bulges are slightly ahead of the Moon’s position. That small offset creates a gravitational tug that transfers energy from Earth’s spin to the Moon’s orbit.
As a result, Earth’s rotation gradually slows, and the Moon slowly drifts farther away.
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Scientists have confirmed this through lunar laser ranging experiments that bounce lasers off reflectors left on the Moon. Measurements show the Moon is moving away from Earth at about 3.8 centimeters per year. Research published in Geophysical Research Letters indicates that tidal friction increases the length of a day by about 1.7 milliseconds per century over long geological periods.
Millions of years ago, Earth spun faster. Days were shorter. The planet we know today has been gradually easing its pace for billions of years.
Winds, Oceans, and Melting Ice
While the Moon shapes the long-term trend, short-term changes in day length come from much closer to home.
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Earth is not solid and still. Air currents shift. Ocean waters move. Ice melts and redistributes water across the globe. When mass shifts around the planet, Earth’s rotation adjusts slightly to conserve angular momentum. It is similar to how a spinning skater changes speed by moving their arms.
Research published in Science by Clark R. Wilson and colleagues demonstrated that exchanges of angular momentum between the atmosphere and the solid Earth can measurably affect day length. During strong El Niño events, changes in global wind patterns are large enough to alter Earth’s rotation by fractions of a millisecond.
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Melting glaciers and polar ice sheets also play a role. Studies in Nature and Geophysical Research Letters show that as ice melts and water spreads into the oceans, the redistribution of weight slightly slows Earth’s spin. Climate-driven shifts are now part of the broader picture, influencing how long our days last.
Winds, ocean currents, melting ice, and core movements also contribute. Scientists monitor these tiny shifts with precise atomic clocks. This lengthening impacts technology like GPS. Leap seconds are used to keep time aligned, though their future is debated.
Deep Inside the Planet
The surface is only part of the story. Far below our feet, Earth’s liquid outer core moves beneath the solid mantle. These deep flows can exchange angular momentum with the outer layers of the planet.
Research published in Nature Geoscience and Geophysical Journal International has examined how interactions between the core and mantle contribute to decade-scale variations in Earth’s rotation speed. These internal processes explain fluctuations that cannot be traced to winds or oceans alone.
Earth behaves less like a rigid spinning top and more like a layered system in constant motion.
Measuring Time With Extreme Precision
Detecting changes of just milliseconds may sound impossible. Modern science has made it routine.
Atomic clocks maintained by the National Institute of Standards and Technology measure time with extraordinary precision. Very Long Baseline Interferometry tracks Earth’s orientation in space by observing distant quasars. Satellite and lunar laser ranging provide additional data.
The International Earth Rotation and Reference Systems Service monitors these variations and tracks changes in day length down to fractions of a millisecond. This level of precision is not just for scientists. GPS navigation, telecommunications networks, aviation systems, and financial markets depend on exact timing.
When Earth’s rotation drifts, global timekeeping must adjust.
Because Earth’s rotation slowly slows, atomic time and astronomical time gradually drift apart. To keep them aligned, leap seconds have occasionally been added to Coordinated Universal Time since 1972.
The practice has sparked debate in the technology and telecommunications sectors, where even a one-second adjustment can complicate software systems. In 2022, the International Telecommunication Union voted to phase out leap seconds by or before 2035.
The debate highlights something most of us rarely consider. The 24-hour day feels natural and fixed. In truth, it is a human standard layered onto a planet that is constantly shifting.
Earth’s days are getting slightly longer because of the Moon’s pull, shifting air and water, melting ice, and movements deep within the core. The changes are tiny, but they remind us that time is tied to the physical world.
The clock on your wall may seem steady. The planet beneath you is always in motion.
