Month of June Will Be One Second Longer This Year

By Carl Engelking | May 21, 2015 1:24 pm


If your birthday is June 30, our planet has a special gift for you this year. Thanks to Earth’s rotation, your special day will last 24 hours and one second.

Come midnight Coordinated Universal Time June 30, the official time will read 23:59:60 rather than resetting to 00:00:00. The extra second, or “leap second,” is needed to resynchronize our land-based clocks with Earth’s rotation, which is slowing down ever so slightly each year. This is the 26th time we’ve added a second to the day since the practice began in 1972.

The Sands of Time

Psychologically it feels like the days pass more quickly as we get older, but the opposite is actually true. Due to tidal forces between the Earth and the Moon, our planet’s rotation is slowing down, adding a whopping 1.4 milliseconds to our days every century. You probably didn’t notice.

However, 1.4 milliseconds add up over time. During the time of the dinosaurs, the typical day on Earth was just 23 hours. In fact, the last true 24-hour rotation, exactly 86,400 seconds, occurred in 1820. Since then, the day has lengthened by 2.5 milliseconds, according to NASA. We have these precise measurements thanks to punctual NASA scientists who have been monitoring Earth’s rotation using a technique called Very Long Baseline Interferometry (VLBI).

A One-Second Headache

Adding an additional second to the day certainly won’t ruin the day for the vast majority of people, unless you are an unprepared computer programmer. The last leap second, in 2012, wreaked havoc on popular websites with clocks synced to standard civil time. Websites like Reddit, FourSquare, Yelp and LinkedIn all reported problems with the change.

When the clock strikes midnight, the 59th second is repeated twice, or a 60th second appears, in order to sync time. However, this puts some computers into a panic because they register this as an error and their CPUs can overload. To avoid this Google added a millisecond of time to their servers with each update so they were caught up with the new time when the leap second occurred.

The U.S. wants to avoid all this trouble by eliminating the leap second altogether, but who are we to deny someone an extra moment of birthday bliss?


Photo credit: rukxstockphoto/Shutterstock

CATEGORIZED UNDER: Space & Physics, top posts
MORE ABOUT: math, physics
  • Dan Foley

    I’ll bet the government will add the 1 second between the hours of 9 and 5 so the productivity numbers for June will look better.

    • Fred Derf

      Read the article for when the added second occurs.

  • Dan Foley

    Fred, you read the article again. It only told what the time will be at at midnight. It didn’t say that the second will be added then. Get a life. Sheesh…

  • JoeD912

    Just curious… how do you reconcile “This is the 26thtime we’ve added a second to the day since the practice began in 1972” with “adding a whopping 1.4 milliseconds to our days every century”? Something seems awry.

    • kvineyard

      The author is saying the Earth day gets longer by 0.0014 seconds every century. So if our day was exactly 24 hrs long in 1820, in 1920 it would be 24hrs +0.0014 seconds, and in 2020 it would be 24hrs +0.0028 seconds. The article says, as of right now, a day is 24hrs +0.0025 seconds.

      But the error accumulates every day. So if a day is currently 24hrs +0.0025 seconds, after 400 days our clock would be off by a full second. So every so often they add a “leap second” to correct the time of our clocks. Just like every 4 years we add a leap day to correct our calendars because our year is actually 365.25 days.

      • JoeD912

        So these are not two statements about the same rate of change. Apparently it’s the 26th time we’ve added a second since 1972 to correct an error of 1.4 ms/century since forever. If that’s the interpretation, I wonder if this correction finishes it or if we’re still in the hole (and for how much longer until we’re caught up and correcting only at the 1.4 ms/century rate vs. the 1 sec every 1.6 yrs.)

        • JoeD912

          OK, I reread what you wrote and I think I finally got the distinction between the error on a daily basis vs the rate of change to the error over a century. Thanks for the explanation… just a little slow on my part. 😉

          • kvineyard

            NP. I had to reread that part of the article as well.

  • Fred F

    There are two corrections going on here. If it was just the lengthening of the year (0.0025 milliseconds per day) then since 1972 (43 years or about 15,705 days ago) we would need to have corrected 39 seconds (15705 x 0.0025). But the article mentions only 26 corrections. The other correction built into this system is to correct the Gregorian calendar system which is the one we use now. The average length of the year is 365.24219 days per Wikipedia. The older Julian calendar was
    based on a year of 365.2500 days and accounted for the extra 0.25 days
    with a leap day every four years. But because this is not the true length,
    the calendar drifted by about a day per century. By the time of Pope Gregory this had amounted to 11 days and the dates were getting out of synch with the seasons. The Gregorian calendar system took into account the fact that the real length was just under 365.25 and eliminated one leap year per century, which occurs on years ending with 00. This is still not perfect but now leap seconds are used to keep the calendar in synch.


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