In 2020, Earth's rotation actually sped up, making people wonder whether we'd need to remove a leap second for the first time. Some years there have been more than one, some years there have been none at all. The first leap second was added in 1972, and there have been 26 more since.

This involves making regular adjustments called 'leap seconds'. To prevent the atomic clocks running away with themselves as Earth slows down, the IERS tries to keep Coordinated Universal Time and Universal Time to within 0.9 seconds of each other. They then combine this with International Atomic Time to get a final figure for Coordinated Universal Time. The International Earth Rotation and Reference Systems Service (opens in new tab) (IERS) measure Earth time, known as Universal Time, by watching the stars race past as the planet spins. To account for this natural variation, the world clock also takes Earth's rotation into account. (opens in new tab)If we set our clocks by it, we'd soon be waking up for breakfast in the middle of the night.

The irregularity in Earth's spin means that International Atomic Time is now running 37 seconds fast. It fluctuates from day to day, and it's gradually slowing down. But in practice, Earth's rotation is slightly irregular. In theory, our planet spins on its axis once every 24 hours. Was Einstein wrong? The case against space-time theoryĪtomic time is so precise that Earth itself can't keep up. Can we time travel? A theoretical physicist provides some answers Electrons: Facts about the negative subatomic particles

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