Re: [LEAPSECS] The real problem with leap seconds

From: William Thompson <William.T.Thompson.1_at_GSFC.NASA.GOV>
Date: Fri, 13 Jan 2006 14:25:13 -0500

I don't know about a canonical list, but one standard document that is used
within NASA is CCSDS 301.0-B-3, which is available from the Consultative
Committee on Space Data Systems website at

This standard references ISO-8601, and is partially based on it.

Bill Thompson

Warner Losh wrote:
> 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

William Thompson
NASA Goddard Space Flight Center
Code 612.1
Greenbelt, MD  20771
Received on Fri Jan 13 2006 - 11:25:32 PST

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