This year, the world will earn an extra second. The International Earth Rotation Service has ruled that the tweak is necessary to keep the world’s most accurate clocks synced to the realities of the Earth’s rotation—which is slowing down.
The change will occur right before midnight on the night of June 30th, 2015 — when clocks run on atomic time will go from 11:59:59 to 11:59:60 instead of switching right over to the next day. The world has gained 15 of these “leap seconds” since the very first in 1972, according to the Guardian.
So what is atomic time? It’s a measurement based on vibrations within atoms, which have proven more accurate than any other method of time-keeping that humans have come up with to date. It's even more precise than the spin of the Earth, which tends to wobble.
As Adam Hadhazy of LiveScience explains:
When exposed to certain frequencies of radiation, such as radio waves, the subatomic particles called electrons that orbit an atom's nucleus will "jump" back and forth between energy states. Clocks based on this jumping within atoms can therefore provide an extremely precise way to count seconds.
Many modern atomic clocks measure these jumps in cesium. The U.S. built one of the world’s most accurate clocks to keep the nation’s official time. It is maintained by the National Institute of Standards and Technology in one of 60 laboratories around the world that contribute data to help determine universal time. (Should you ever need to know the exact time in the U.S., just visit this website.)
Not everyone loves the leap second, though, as Paula Cocozza of the Guardian points out:
Some of the 170 countries represented at the International Telecommunication Union — the US, France, Mexico and Japan, for instance — want to end the leap second and simply let atomic clocks run away from Earth.
Why argue against extra time? One reason might be that the micro-adjustment causes problems for the internet. During the last leap second in 2012, websites including Foursquare, Reddit, LinkedIn and Yelp experienced problems, as Bob Yirka at Phys.org notes.
Google has been hard at work making sure that this year’s leap second doesn’t cause any issues for its many services. Engineers there may have found a creative solution, according to James Vincent of The Verge:
As the company’s site reliability engineer Christopher Pascoe explained in a blog post, the usual fix is to turn back the clocks by one second at the end of the day, essentially playing that second again. However, says Pascoe, this creates problems: "What happens to write operations that happen during that second? Does email that comes in during that second get stored correctly?" Google’s solution is to cut the extra second into milliseconds and then sprinkle these tiny portions of time into the system imperceptibly throughout the day.
How will it all play out? Only time will tell.