[110435] in North American Network Operators' Group
Re: Leap second tonight
daemon@ATHENA.MIT.EDU (Peter Beckman)
Mon Jan 5 16:19:39 2009
Date: Mon, 5 Jan 2009 16:19:28 -0500
From: Peter Beckman <beckman@angryox.com>
To: NANOG list <nanog@nanog.org>
In-Reply-To: <6F0A37B2-75B8-4E71-A3F3-40DC100B2D7B@multicasttech.com>
Errors-To: nanog-bounces@nanog.org
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
manufacturer/OS/software.
* 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.
Beckman
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.
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