Re: [LEAPSECS] The real problem with leap seconds

From: Warner Losh <imp_at_BSDIMP.COM>
Date: Fri, 13 Jan 2006 11:32:36 -0700 (MST)

From: Ed Davies <ls_at_EDAVIES.NILDRAM.CO.UK>
> Markus Kuhn wrote:
> > Ed Davies wrote on 2006-01-13 11:45 UTC:
> >
> >>The use of the 23:59:60 notation is described in ISO 8601.
> >>Is it also specified in TF.460?
> >
> >
> > It originally comes from ITU-R TF.460, which is a standard for radio
> > time signals.
>
> OK, thanks.

Has anybody compiled a canonical list of the standards in this area?
This is the first, I think I've seen ISO 8601 mentioned.

TF.460 doesn't talk about days at all, really, or MJD. It doesn't
talk about rendering a time a floating point number, only as the
traditional sexagesimal fractional time, with the 'execption' during
the positive leap second.

If we explore the orgins of the time
        12:34:56 (just after noon)
we note that it is in the 13th 1/24th division of a day (since the 0th
(aka 12) hour is first), the 35th 1/60th division of the 1/24th
division (since the first one is 0) and the 56th 1/60th division of
the 1/60th division of the 1/24th division a day. Labeling the
positive leap second as
        23:59:60
leads to some trouble if we try to work backwards through the above
derivation. It creates an exception to the nice, orderly rules of
time. But I'm digressing...

The ITU-R TF.460 states:

2.2 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 (see Annex III).

2.3 The IERS should decide upon and announce the introduction of a
leap-second, such an announcement to be made at least eight weeks in
advance.

In Annex III, it talks about the dating of events during the positive
leap second. If something were to happen .6s into that second, it
would be denoted (assuming a june leap) as:

        30 June, 23h 59m 60.6s UTC

(the document has h, m and s superscripted, and the European (?) style
centered decimal point)

Warner
Received on Fri Jan 13 2006 - 10:36:06 PST