text: Clouds over Australia are shown. Credit: NASA As if 2016 has not been long enough, the year's dying minute will last an extra second to make up for time lost to Earth's slowing rotation, timekeepers say. 
   
   Countries that use Coordinated Universal Time—several West African nations, Britain, Ireland and Iceland—will add the leap second during the midnight countdown to 2017—making the year's final minute 61 seconds long. 
   
   For others, the timing will be determined by the time zone they live in, relative to UTC. 
   
   "This extra second, or leap second, makes it possible to align astronomical time, which is irregular and determined by Earth's rotation, with UTC which is extremely stable and has been determined by atomic clocks since 1967," the Paris Observatory said in a statement. 
   
   The observatory houses the International Earth Rotation and Reference Systems Service (IERS), responsible for synchronising time. 
   
   "The sequence of dates of the UTC second markers will be: 2016 December 31 23h 59m 59s, 2016 December 31 23h 59m 60s, 2017 January 1, 0h 0m 0s," the IERS website states. 
   
   The adjustment is necessary because Earth's rotation is not regular—it sometimes speeds up, sometimes slows down, but is gradually slowing overall. 
   
   This is caused by factors including the Moon's gravitational Earth-braking forces, which give rise to the ocean tides. 
   
   The result is that astronomical time—based on the length of an Earth day— gradually falls out of sync with atomic time—which is measured by nearly 400 super-accurate atomic clocks dotted around the world. 
   
   Leap year, too 
   
   Atomic time or TAI, in turn, is used to determine UTC, used for civil timekeeping globally. 
   
   TAI is exactly 36 seconds ahead of UTC, a difference that keeps growing as leap seconds are added, and will reach 37 seconds on January 1. 
   
   When leap seconds were introduced in 1972, 10 seconds had to be added to UTC, followed by another roughly every 18 months thereafter, according to the National Institute of Standards and Technology (NIST) of the US Department of Commerce. 
   
   The last was added on June 30, 2015. 
   
   "Leap seconds are added in order to keep the difference between UTC and astronomical time (UT1) to less than 0.9 seconds," the NIST website explains. 
   
   "Usually leap seconds are added when UTC is ahead of UT1 by 0.4 seconds or more." 
   
   The process, it added, can create problems for data logging applications and telecommunications systems. 
   
   "Special attention must be given to these systems each time there is a leap second." 
   
   2016 has also had a leap day—February 29—a four-yearly occurrence to keep the calendar synchronised with Earth's movement around the Sun. 
   
   Explore further: 2016 will be one second longer ||||| Share this page! 
   
   Time zone 
   
   Coordinated Universal Time (UTC), UTC +0 
   
   The IANA time zone identifier for UTC is UTC. ||||| What leap seconds are, how they are implemented and their future. 
   
   What is a leap second? 
   
   A leap second is a second added to Coordinated Universal Time (UTC) in order to keep it synchronized with astronomical time. UTC is an atomic time scale, based on the performance of atomic clocks that are more stable than the Earth's rotational rate. Astronomical time (UT1), or mean solar time, is based on the rotation of Earth, which is irregular. 
   
   
   
   There are two main reasons that cause leap seconds to occur. The first is that the duration of the atomic second was measured and defined by comparing cesium clocks to the Ephemeris Time (ET) scale, an obsolete time scale that defined the second as a fraction of the tropical year. The duration of the ephemeris second was slightly shorter than the mean solar second and this characteristic was passed along to the atomic second. If the atomic second had been defined with respect to the mean solar second, it is likely that leap seconds would have been required much less frequently. The second reason for leap seconds is that the speed of the Earth's rotation is not constant. It sometimes speeds up, and sometimes slows down, but when averaged over long intervals the trend indicates that it is gradually slowing. This gradual decrease in the rotational rate is causing the duration of the mean solar second to gradually increase with respect to the atomic second. 
   
   
   
   For information about past leap seconds and the measured differences between UTC and UT1, please see the NIST Time Scale Data Archive. 
   
   How often do we have leap seconds? 
   
   Leap seconds are added in order to keep the difference between UTC and astronomical time (UT1) to less than 0.9 seconds. The International Earth Rotation and Reference Systems Service (IERS), measures Earth's rotation and publishes the difference between UT1 and UTC. Usually leap seconds are added when UTC is ahead of UT1 by 0.4 seconds or more. At the time the corrections started in 1972, a necessary correction of ten seconds was made to UTC, and there have been leap seconds about every year and a half (on average). The current difference between UTC and UT1 is shown in our leap second archive web page. 
   
   When do leap seconds occur? 
   
   Leap seconds have always occurred at the end of December or the end of June, on the last second of the UTC day. The designation of the sequence of seconds is: 
   
   
   
   23h 59m 59s 
   
   23h 59m 60s 
   
   00h 00m 00s 
   
   
   
   Are there benefits and/or detriments to adding leap seconds? 
   
   By keeping Coordinated Universal Time (UTC) within one second of astronomical time, scientists and astronomers observing celestial bodies can use UTC for most purposes. If there were no longer a correction to UTC for leap seconds, then adjustments would have to be made to time stamps and legacy equipment and software which synchronize to UTC for astronomical observations. However, adding a second to UTC can create problems for some systems, including data logging applications, telecommunication systems and time distribution services. Special attention must be given to these systems each time there is a leap second. 
   
   What is the future of leap seconds? 
   
   Some proposals have been made to implement larger corrections like leap hours, which would occur much less often than leap seconds. Also, it has been suggested to stop corrections to UTC and publish the growing difference between UTC and UT1. The relatively small community that needs UT1 could then use the published values as a correction. Discussions of the future of leap seconds are ongoing at meetings of the Radiocommunication Sector of the International Telecommunication Union (ITU-R). 
   
   How is a leap second related to a leap year? 
   
   Leap seconds and leap years are both implemented to keep our time in accordance with the position of Earth. However, leap seconds are added when needed, based on measurements, and leap years are regularly occurring events based on set rules. During leap years, an extra day is added as February 29th to keep the calendar synchronized with the precession of the Earth around the Sun. Leap years are necessary because the actual length of the year is 365.2422 days and not 365. The extra day is added every four years to compensate for most of the partial day. However, this is a slight over-compensation, so some century years are not leap years. Only every fourth century year (those equally divisible by 400) is a leap year. For instance, 2000 was a leap year, but 1900, 1800 and 1700 were not. 
   
   
   
   For additional information about leap years, please see the exhibit on calendars on our time exhibits page. ||||| If you can't wait for 2016 to be over, I have some bad news; it's going to be a little bit longer than expected. In July of this year, the International Earth Rotation and Reference Systems Service (IERS)—which regulates the international clock—announced that 2016 will end in a leap second. An extra tick will be inserted into the year to make up for unpredictable variations to the Earth's rotation, and that means before we hop into 2017, the clock will strike an unusual 23:59:60. 
   
   Leap seconds are not particularly strange. We had one back in the summer of 2015, and when everybody is ready for one, you hardly even notice that anything has happened. But these leap seconds do pose unique problems for timekeeping computers, which are unable to conceive of a 61st second by the very nature of their coding. In a way, it's a Y2K-esque problem. Simple math for a human, borderline brain-frying for a computer. 
   
   This is a particular problem for companies like Google, which run Network Time Protocol servers, internet clocks your laptop sets its watch to. The immediately obvious solution is to add an extra second to these servers, bam. But as Google points out in a blog post, that's not as easy as it sounds because most computers and operating systems don't understand a 61st second. In order for that to work, literally every device involved has to understand that something weird is going on and that's only happening this one time. In the past, attempting this solution has caused a number of real problems. 
   
   So Google came up with a different, extremely elegant plan. The weird part is that it will take 20 hours: 
   
   Instead of adding a single extra second to the end of the day, we'll run the clocks 0.0014% slower across the ten hours before and ten hours after the leap second, and "smear" the extra second across these twenty hours. 
   
   If you check the math you can see how this "smeared time" works: 
   
   20 hours = 1,200 minutes = 72,000 seconds 
   
   72,000 seconds x .000014 (.0014%) = 1.08 seconds 
   
   Though given that extra .08 second on there, it seems like the .0014% number is probably rounded, or altered in some other way. 
   
   This isn't a brand new idea. Google's first came up with it in 2008, and other companies in similar positions have tried variations, though the specifics vary. For the 2015 leap second, Amazon Web Services slowed its clocks by 1/86400 (.001157407%) for a day before the jump, smearing the extra second over the preceding 24 hours so its clocks would be one second slow at the time of the one-second jump. Another cloud company, Akamai, is doing the same thing this year, using a 24-hour smear. 
   
   Google's 20-hour smear is an outlier, but not due to any illusions that this method is superior. As Google's developer page notes, the choice is to make things easy on Google's existing infrastructure, and the company proposes that everyone adopt a standard noon-to-noon, 24-hour smear, with the leap second dead center, instead of on the end. 
   
   The end result? With any luck you won't notice a damn thing. But when you're watching the clock tick down to the first second of 2017, take a moment to appreciate all the math that's being put to work to give you that precious little quantifiable illusion we call time. ||||| Like a man eager to show off his new watch, Google is encouraging anyone running IT operations to ask it for the time. 
   
   The company will let anyone use its NTP (Network Time Protocol) servers, a move to help IT shops cope with the next “leap second,” which will be tacked onto 2016 just after midnight on Dec. 31. 
   
   Leap seconds help to keep clocks aligned with Earth’s rotation, which can vary due to geologic and even weather conditions. But an extra second can wreak havoc with applications and services that depend on systems being tightly synchronized. 
   
   Most Internet-connected devices get their time through NTP, an open-source technology that's used all over the world. NTP has its own problems, mainly around funding, but it's long been the standard. Google runs its own NTP servers and uses them to ease its systems through leap seconds, according to Michael Shields, technical lead on the company’s Time Team, in a blog post on Wednesday. 
   
   Time synchronization is critical for many things Google’s systems do, such as keeping replicas up to date, determining which data-affecting operation happened last, and correctly reporting the order of searches and clicks, the company says. 
   
   Ordinary operating systems can’t accommodate a minute that’s 61 seconds long, so some organizations have used special-case workarounds for the extra second. But sometimes these methods raise issues, like what happens to write operations that take place during that second. At times in the past, some Google systems have refused to work when faced with a leap second, though this didn’t affect the company’s services, a Google representative said. 
   
   So Google will modify its NTP servers to run clocks 0.0014 percent slower for 10 hours before the leap second and for 10 hours afterward. When the leap second takes place, they will have accounted for it already. Google’s been using this technique, called “smeared time,” since a leap second in 2008. 
   
   Enterprises running virtual-machine instances on Google Compute Engine, and those using Google APIs, will want to keep their own systems synchronized with Google’s slightly slower clocks during that 20-hour period. Client systems will also have to be set to that time in order to work with those servers. And it won’t work to run some servers on smeared time and some on regular time, because then clients won’t know which time to follow, Google says. 
   
   So the company is making its NTP servers available free through the Google Public NTP service. Users can take advantage of the service by configuring their network settings to use time.google.com as their NTP server. The company laid out detailed instructions for synchronizing systems to its smeared time. 
   
   Google won’t be the only company smearing time on Dec. 31. Akamai plans to slow down its clocks over a 24-hour period around the leap second. Amazon and Microsoft have done the same thing in the past. 
   
   In fact, the big cloud companies look ready to standardize on a 24-hour “leap smear.” Google plans to use the longer transition for the next leap second, partly to ease more slowly into extra second and partly to align itself with other companies. There’s no date yet for the next leap second, but Google expects it to come in 2018. 
   
   Leap seconds began in 1972 and are now administered by the International Earth Rotation and Reference Systems Service (IERS). They’re needed because Earth’s rotation isn’t uniform. It’s affected by things like tides in the oceans and the movement of magma beneath the Earth’s crust. Atomic clocks, which set the standard for most timekeeping, are more consistent than that.
target: – For many, 2016 can't end soon enough. For everyone, though, it's actually going to last one second longer than usual. With New Year's Eve approaching, outlets such as Phys.org are reminding people that an extra "leap second" will be added to the final day of 2016 in order to keep our earthly time-keeping measures in sync. No, this won't affect countdowns to ball drops—the second is incorporated into the day in far more subtle ways—but if you happened to watch the online clock counting Coordinated Universal Time, or UTC, you'd see the quirk of it going from 23:59:59 to 23:59:60, instead of flipping to 00:00:00. A more technical explanation: "Leap seconds are added in order to keep the difference between UTC and astronomical time (UT1) to less than 0.9 seconds," per the National Institute of Standards and Technology. Wonky, yes, but for companies such as Google that operate Network Time Protocol servers, the leap second is indeed a big deal—and a post at Popular Mechanics praises the company's "extremely elegant solution" to the issue. Google will "smear" that extra second, as it explains in a blog post. "Instead of adding a single extra second to the end of the day, we'll run the clocks 0.0014% slower across the ten hours before and ten hours after the leap second, and 'smear' the extra second across these twenty hours." Other cloud companies such as Akamai use a similar approach but over 24 hours, notes PCWorld, which expects this longer "leap smear" to be standard when the next leap second rolls around, probably in 2018. (If you're planning a trip to ring in 2017 somewhere, this list might help.)