The deaths of great artists, global tragedies, an acrimonious U.S. presidential campaign — these events have made many of us are eager to get the seemingly interminable nastiness that was 2016 over with, once and for all. But thanks to the precision of modern timekeeping, we'll have to wait one additional second on New Year's Eve before we can welcome what hopefully will be a better 2017.
The additional second will be inserted precisely one second before midnight strikes at the Royal Observatory at Greenwich in England. Since 1884 that's been the location of the Prime Meridian for Greenwich Mean Time, also known as Coordinated Universal Time (UTC), which sets the standard for the rest of the world's time zones. Because that spot is five hours ahead of U.S. Eastern time, the additional second will be inserted at one second before 7 p.m. at the U.S. Naval Observatory's Master Clock Facility in Washington, D.C., which sets the time for Americans.
Why is this necessary? For most of history, people used Earth itself as a giant clock, under the assumption that it always rotated at the same precise speed. But with the development in the 1940s of the first atomic clock, which used the vibration of the cesium atom to measure units of time, it became apparent that the planet isn't all that dependable of a clock. That's because the planet's rotation is very, very, very slowly decreasing — by about 0.002 seconds per day. That means that every 18 months, it loses about one second of time. (Atomic clocks, in comparison, typically lose about a billionth of a second per day.)
That discrepancy between atomic clocks and Earth results in some complications, because we still use our planet's rotation as the basis for the calendar. To compensate, the International Telecommunications Union, an agency of the United Nations that helps to regulate time across the world, adds a second to UTC every so often to even things out. And this isn't the first time a so-called "leap second" has been added to a year. We've done so 27 times ever since 1971, either on June 30 or Dec. 31.