[154433] in North American Network Operators' Group
Re: F-ckin Leap Seconds, how do they work?
daemon@ATHENA.MIT.EDU (Owen DeLong)
Tue Jul 3 20:36:17 2012
From: Owen DeLong <owen@delong.com>
In-Reply-To: <49423.1341348864@turing-police.cc.vt.edu>
Date: Tue, 3 Jul 2012 17:34:37 -0700
To: Valdis.Kletnieks@vt.edu
Cc: NANOG <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Jul 3, 2012, at 1:54 PM, Valdis.Kletnieks@vt.edu wrote:
> On Tue, 03 Jul 2012 21:49:40, Peter Lothberg said:
>=20
>> Leapseconds can be both positive and negative, but up to now, the
>> earth has only slowed down, so we have added seconds.
>=20
> That's what many people believe, but it's not exactly right. Leap =
seconds
> are added for the exact same reason leap days are - the earth's =
rotation
> isn't a clean multiple of the year. We know we need to stick in an =
entire
> leap day every 4 years or so, then add the 400 hack to get it closer. =
At
> that point, it's *really* close, to the point where just shimming in a =
second
> every once in a while is enough to get it back in sync.
>=20
IIRC, isn't it:
Add a leap day every 4 years.
Exception: If the year ends in 00, do not add a leap day. (an exception =
seemingly glossed over in the thread so far)
Exception to the exception: If the year is a multiple of 400, add a leap =
day. (so called 400 hack)
With that set of rules, we get close enough to only fudge by a second =
here and there.
Owen
