[ntp:questions] Leap second to be introduced in June

William Unruh unruh at invalid.ca
Sun Jan 18 23:04:58 UTC 2015

On 2015-01-18, Mike S <mikes at flatsurface.com> wrote:
> On 1/13/2015 11:46 PM, William Unruh wrote:
>> That is a translation from seconds to ymdhms. The problem is not there.
>> it is in the UTC seconds.
>> In UTC one second disappears after the leap second, but not before or
>> during. Thus UTC seconds numbering is simply disconinuous (jumps back) .
> UTC jumps neither forward nor backwards. UTC simply allows minutes of 
> 59, 60 or 61 seconds. There is NO discontinuity. The canonical form of 
> UTC (and TAI) is ymdhms.

UTC always has 86400 seconds per year. 

> TF.460 describes very clearly how UTC is enumerated. "A positive 
> leap-second begins at 23h 59m 60s and ends at 0h 0m 0s of the first day 
> of the following month. In the case of a negative leap-second, 23h 59m 
> 58s will be followed one second later by 0h 0m 0s of the first day of 
> the following month"
> http://www.itu.int/rec/R-REC-TF.460-6-200202-I/en
B International atomic time (TAI)
The international reference scale of atomic time (TAI), based on the
second (SI), as realized on the
rotating geoid, is formed by the BIPM on the basis of clock data
supplied by cooperating
establishments. It is in the form of a continuous scale, e.g. in days,
hours, minutes and seconds from
the origin 1 January 1958 (adopted by the CGPM 1971). 

Note: It is in the form of a continuous scale. 

C Coordinated universal time (UTC)
UTC is the time-scale maintained by the BIPM, with assistance from the IERS, which forms the
basis of a coordinated dissemination of standard frequencies and time signals. It corresponds
exactly in rate with TAI but differs from it by an integer number of seconds.
The UTC scale is adjusted by the insertion or deletion of seconds (positive or negative leapseconds)
to ensure approximate agreement with UT1. 

Note UTC differs from TAI by an interger number of seconds, AND that
integer changes with the leap second. Ie, it cannot be continuous if TAI
is continuous. 

> The issue you're describing is an issue with POSIX time, which doesn't 
> handle leap seconds.

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