[tz] Leap seconds puzzle

Steve Allen sla at ucolick.org
Wed Apr 8 19:17:58 UTC 2015

On Wed 2015-04-08T19:02:07 +0000, Paul_Koning at dell.com hath writ:
> So here is the puzzle.  I would expect WWV, and www.time.gov, to
> reflect leap seconds.  So why would they give me a time that matches,
> to the second, the POSIX time on my workstation?  Does NTP send POSIX
> seconds since epoch rather than real ones?

NTP effectively sends "mean solar seconds elapsed since epoch", which
is another way of saying "elapsed seconds not counting leap seconds"
as is demanded by POSIX.

The value of the time in WWV and www.time.gov is conforming to ITU-R
TF.460 where the leap seconds in the radio broadcasts were designated
as 23:59:60 in order that the value of SI second markers of UTC
closely matches the value of mean solar second markers of UT1.  In
the radio broadcasts those leap seconds are truly intercalary.
There is no way for the value of the time in WWV to indicate the
number of times that an intercalary second has been inserted since
1972, nor when they were inserted.

Before 1972 there was no way for the value of the time in WWV to
indicate the number of leaps of milliseconds, nor the number of times
that the duration of the broadcast seconds had been changed, nor the
current duration of the broadcast seconds.

Steve Allen                 <sla at ucolick.org>               WGS-84 (GPS)
UCO/Lick Observatory--ISB   Natural Sciences II, Room 165   Lat  +36.99855
1156 High Street            Voice: +1 831 459 3046          Lng -122.06015
Santa Cruz, CA 95064        http://www.ucolick.org/~sla/    Hgt +250 m

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