F-ckin Leap Seconds, how do they work?

Owen DeLong owen at delong.com
Wed Jul 4 00:34:37 UTC 2012

On Jul 3, 2012, at 1:54 PM, Valdis.Kletnieks at vt.edu wrote:

> On Tue, 03 Jul 2012 21:49:40, Peter Lothberg said:
>> Leapseconds can be both positive and negative, but up to now, the
>> earth has only slowed down, so we have added seconds.
> 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.

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.


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