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Re: Leap second tonight
From: Peter Beckman <beckman () angryox com>
Date: Mon, 5 Jan 2009 16:19:28 -0500

I've gleened from this thread that:

    * everyone uses UTC, or should, because UTC is a uniform time scale,
      except for those leap seconds
    * UTC is sourced from the frequence of a radio emission from cesium
      atoms which are extremely constant
    * UTC can get out of whack with the rotation of the earth around the
      sun, because our rotation is not uniform, but is calculated rather
      than measured (well, sort of)
    * UTC is TAI plus leap seconds.  In 1972, when leap seconds were first
      introduced, UTC was TAI - 10 seconds.  UTC is now TAI - 34 seconds.
      TAI ticks exactly as fast as UTC, ignoring leap second adjustments.
    * UTC is slower than UT1 by about 1ms per day.
    * On 12/31/2008 UTC was (-) 591.8ms behind UT1.  On 1/1/2008 UTC was
      407.1ms ahead of UT1.
    * Leap seconds are applied to UTC every few years to remain in line
      with UT1, the time based on the rotation of the earth around the sun.
    * GMT is used to imply UT1, but sometimes UTC, but really GMT is just
      massively confusing and you shouldn't use it, either in conversation
      or in your servers/routers, because nobody is really sure without
      reading a lot of documentation what GMT means for each
    * When writing code regarding dates and times, know that any year may
      have 366 days, and any minute may have 61 seconds.
    * When in doubt, Dr.  Daniel Gambis is always right.


On Mon, 5 Jan 2009, Marshall Eubanks wrote:

Having been involved in the leap second business, I can tell you that
Daniel Gambis strictly follows the rules, which are Bulletin C is mailed
every six months, either to announce a time step in UTC or to confirm
that there will be no time step at the next possible date.

Peter Beckman                                                  Internet Guy
beckman () angryox com                                 http://www.angryox.com/

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