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July 1st Delayed: Leap Second Inserted

posted by janrinok on Monday June 29 2015, @10:35PM   Printer-friendly
from the hang-on-a-second dept.

sudo rm -rf writes:

Mainly due to the slowing down of earth rotation, it is about time to add another (the 35th) leap second to UTC in order to keep its time of day close to the mean solar time. NASA features an explanation of why the leap seconds have to be inserted, how earth rotation can be measured precisely and why it is impossible to give precise predictions on when the next one will happen.

The length of day is influenced by many factors, mainly the atmosphere over periods less than a year. Our seasonal and daily weather variations can affect the length of day by a few milliseconds over a year. Other contributors to this variation include dynamics of the Earth's inner core (over long time periods), variations in the atmosphere and oceans, groundwater, and ice storage (over time periods of months to decades), and oceanic and atmospheric tides. Atmospheric variations due to El Niño can cause Earth's rotation to slow down, increasing the length of day by as much as 1 millisecond, or a thousandth of a second.

VLBI [Very Long Baseline Interferometry] tracks these short- and long-term variations by using global networks of stations to observe astronomical objects called quasars. The quasars serve as reference points that are essentially motionless because they are located billions of light years from Earth. Because the observing stations are spread out across the globe, the signal from a quasar will take longer to reach some stations than others. Scientists can use the small differences in arrival time to determine detailed information about the exact positions of the observing stations, Earth's rotation rate, and our planet's orientation in space.

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  • (Score: 2) by sudo rm -rf on Tuesday June 30 2015, @05:11AM

    by sudo rm -rf (2357) on Tuesday June 30 2015, @05:11AM (#203190) Journal

    I wouldn't worry to much, but if you encounter any problems, I'm sure it would make a nice story!
    BTW, Google [blogspot.se] has come up with it's own solution fo fix the leap seconds, by slowing down server time.

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  • (Score: 2) by pkrasimirov on Tuesday June 30 2015, @06:49AM

    by pkrasimirov (3358) Subscriber Badge on Tuesday June 30 2015, @06:49AM (#203207)

    Solaris has this for a long time:

    date(1)

    ...

      -a [ - ] sss.fff

            Slowly adjust the time by sss.fff seconds (fff represents fractions of a second). This adjustment can be positive or negative. The system's clock is sped up or slowed down until it has drifted by the number of seconds specified. Only the super-user may adjust the time.

    https://docs.oracle.com/cd/E19253-01/816-5165/6mbb0m9dc/index.html [oracle.com]

    • (Score: 0) by Anonymous Coward on Tuesday June 30 2015, @07:54AM

      by Anonymous Coward on Tuesday June 30 2015, @07:54AM (#203228)

      From the ntpdate man page: [unix.com]

      OPTIONS
      [...]
       
             -B     Force the time to always be slewed using the adjtime() system  call,  even  if  the
                measured    offset    is  greater  than +-128 ms. The default is to step the time using
                settimeofday() if the offset is greater than +-128 ms. Note that, if the offset  is
                much  greater  than  +-128 ms in this case, that it can take a long time (hours) to
                slew the clock to the correct value. During this time, the host should not be  used
                to synchronize clients.