Earth is now spinning faster than it did 50 years ago

The last leap second was added in 2016, but Earth’s rotation has been speeding up since.

Key Takeaways

• Earth’s rotation has unexpectedly sped up, shortening days slightly compared to 50 years ago.
• This faster spin challenges long-held trends of Earth’s gradual slowdown due to the moon’s pull.
• Leap seconds are added to atomic clocks to synchronize with Earth’s variable rotation.
• A potential need for “negative leap seconds” could disrupt technology reliant on precise timing.
• Factors influencing Earth’s spin include atmosphere, oceans, and complex Earth-moon interactions.

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Why Earth is Spinning Faster

Earth’s rotation has been speeding up over the past decade, leading to the shortest days observed in 50 years. Scientists are puzzled by this surprising deviation from the planet’s usual behavior of slowing down gradually. Typically, Earth’s rotation has been influenced by factors like the moon’s gravitational pull, which creates drag through tidal forces, and the distribution of mass across the planet.

The current faster spin comes after centuries of relatively stable rotation rates. In ancient times, Earth completed about 420 rotations per year during its orbit around the Sun, evidenced by fossil coral records. Over time, the moon’s effect slowed Earth, lengthening days to about 24 hours. However, since 2016, Earth’s rotation has been speeding up, eliminating the need for the leap seconds scientists introduced in the 1970s.

Leap Seconds: Balancing Time and Rotation

Leap seconds were first added in 1972 to align atomic time, which is incredibly precise, with Earth’s slightly erratic rotation. Atomic clocks, developed in the 1950s, measure time by tracking electrons in cesium atoms, providing unparalleled accuracy. Discrepancies arose as Earth’s rotation periodically sped up or slowed down, prompting scientists to insert leap seconds when needed to keep both systems in sync.

The International Earth Rotation and Reference Systems Service monitors Earth’s rotation and determines when to add leap seconds. The adjustments are made at 11:59:59 pm on either June 30 or December 31. However, the rapid acceleration of Earth’s spin has introduced the possibility of removing time, known as a “negative leap second.” This has never been done before and could disrupt systems relying on precise and continuous timekeeping, such as telecommunications, navigation, and financial networks.

Google and other companies have developed creative solutions to address leap seconds. Google stretches the length of each second slightly over an entire day to avoid sudden changes, ensuring smoother time synchronization. Despite these workarounds, questions remain about the long-term utility and implications of leap seconds.

Implications and Future Questions

The reasons behind Earth’s current acceleration remain unclear. Factors such as atmospheric dynamics, ocean effects, and tectonic activity could all contribute to fluctuations in rotation speed. While most people won’t notice these changes, they have significant implications for industries that rely on precise timekeeping.

Physicist Judah Levine suggests that leap seconds may cause more problems than they solve, though they preserve humanity’s connection to astronomical time. Without adjustments, atomic clocks and Earth’s rotation could diverge by a minute after more than a century—a small shift for daily life but notable for those measuring time to the millisecond.