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2016 seems long to me (Leap second)

  1. Dec 29, 2016 #1

    jim mcnamara

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    Staff: Mentor

    Now I know why: http://phys.org/news/2016-12-extra_1.html
    We are getting a leap second! 2016 really is too long. :cry: If you are an astronomer or programmer you know about these corrections to NIST atomic clock time (UTC). The Earth's period of rotation is not constant over long periods. Very slightly, Earth slowing down.

    Programming:
    The POSIX standards (for UNIX) do not require tracking leap seconds. But some OS developers have decided to keep track of them - Linux for example. GPS does not deal with them.

    Here is a discussion:
    https://www.wired.com/2015/01/torvalds_leapsecond/
     
  2. jcsd
  3. Dec 29, 2016 #2
  4. Dec 29, 2016 #3

    1oldman2

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    Interesting, I would have assumed one second would be fairly crucial, I thought GPS even took time dilation into account. Am I missing something here. ?
     
  5. Dec 29, 2016 #4

    jim mcnamara

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    Staff: Mentor

    Oops - the second will be added to 2017, my apologies.

    NIST source file for programming - leap seconds: https://github.com/eggert/tz/blob/master/leap-seconds.list

    @1oldman2 - yes, gps does care about relativity. GPS depends solely on the duration (delay) of the signal until reception time. So all that matters in terms of elapsed time is that: Every satellite is on the same time precisely, and the ephemeris portrays the exact sub-satellite point Then corrections like WASD, are applied to correct for atmospheric refraction. GPS uses its own time standard, which can be converted to UTC.

    There is a LOT to this that I blithely ignored. Links:
    Math: http://www.maa.org/sites/default/files/pdf/cms_upload/Thompson07734.pdf
    Overview: http://www.oc.nps.edu/oc2902w/gps/timsys.html
     
  6. Dec 29, 2016 #5

    1oldman2

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    Thanks, sometimes this entire site could be titled "T.I.L." :smile:
     
  7. Dec 30, 2016 #6

    1oldman2

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    https://www.nasa.gov/feature/goddar...ng-nasas-sdo-adds-leap-second-to-master-clock
    On Dec. 31, 2016, official clocks around the world will add a leap second just before midnight Coordinated Universal Time - which corresponds to 6:59:59 p.m. EST. NASA missions will also have to make the switch, including the Solar Dynamics Observatory, or SDO, which watches the sun 24/7.

    Clocks do this to keep in sync with Earth's rotation, which gradually slows down over time. When the dinosaurs roamed Earth, for example, our globe took only 23 hours to make a complete rotation. In space, millisecond accuracy is crucial to understanding how satellites orbit.
     
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