The Earth's rotation is slowing, so everyone gets an extra second this week

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In case you need a little extra time this week, the last minute of Tuesday, June 30 will contain 61 seconds instead of the usual 60.



The Earth's rotation is slowing, so everyone gets an extra second this week

Atomic clocks around the world will coordinate the leap second, which is necessary to keep Coordinated Universal Time (UTC) — the system that guides most international civil times systems — synced with the Earth's rotation.

On Tuesday, atomic clocks should read 23:59:59, then 23:59:60, before switching over to Wednesday with 00:00:00.

Michael Wouters, head of the Time and Frequency team at Australia's National Measurement Institute told Mashable Australia the leap second is being introduced because the difference between UTC and astronomical time has come close to one second.

Atomic time or UTC is based off highly accurate atomic clocks, but scientists also maintain time scales based on the rotation of the Earth using a technique called Very Long Baseline Interferometry (VLBI) that uses radio telescopes to measure the Earth's orientation. "These two things don't always agree with each other," he said.

NASA explains the process of VLBI measurement in this video.

The discrepancy arises because the Earth's rotation is not always predictable. For one thing, the interaction of the Earth with the gravitational forces of the moon and the sun mean it's gradually slowing down. In fact, leap seconds could occur more frequently in the future, Wouters said.

Other events on Earth like significant earthquakes can affect its movement. Changes in temperature due to weather and seasons can also cause the atmosphere to drag on the rotation of the Earth, which means we could see global warming start to have an impact, he said.

The change is intended to keep the UTC within half a second of astronomical time. "It's taken about three years to accumulate about a half a second difference," Wouters said. "This discrepancy accumulates at the rate of a few thousandths of a second a day."

The decision to add a leap second comes from the International Astronomical Union and the International Union of Geodesy and Geophysics (IERS), which provides data about the Earth's rotation to the global scientific community. In January, the agency advised that a leap second should be introduced into the UTC in June.

According to Wouters, the choice of June 30 is just convention. The introduction of a leap second can happen at the end of any month, but it's typically restricted to the end of December or June. Leap seconds were first introduced in 1972 and have been implemented since as needed, according to NASA.

So, why do we need this leap second every few years? Mostly so UTC time doesn't get out of whack with our conception of time based on sunrise and sunset. "Of course, our experience of time is based on astronomical time," Wouters said. "We expect the sun to come up at a particular time, at a particular time of the year."

While you would eventually notice the sun was coming up later than expected if leap seconds weren't added, it would take a very long time. "It's something in the order of around 500 years or so to get a noticeable difference between UTC and astronomical time if you don't have leap seconds," he added.

The last leap second was added on June 30, 2012. That time around, sites like LinkedIn, Foursquare, Reddit and Yelp experienced technical glitches after web servers had difficulty handling the extra moment.

If the Internet shuts down over this, just take a breath and enjoy it. After all, you just got extra seconds of your life for free.
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