Steve Allen sla at ucolick.org
Tue Oct 13 01:42:16 EDT 2009

On 2009 Oct 12, at 03:27, Zefram wrote:

> The number appears again in the main text:


> As represented in seconds since the Epoch, each and every day

> shall be accounted for by exactly 86400 seconds.

Clearly that number is fiat, and not even some entity with the
authority of Pope Gregory could change it. What remains is primarily
to interpret the meaning of the word "day".

In the time scales for TAI, LORAN-C, GPS, and now BST the word "day"
already has a meaning more clearly communicated by "atomic day".
The length of that "atomic day" is practically equivalent to the
"ephemeris day" of Gauss, as codified by Newcomb, as adopted by IAU,
and as realized by Markowitz, Essen, et al.

Resolution V of the 1884 International Meridian Conference defines
"day" to be a mean solar day. To propose that "day" become redefined
as an "atomic day" is to propose the abrogation of the IMC. It is
plainly outside the scope of the POSIX committee to implement such
a change. They have to rely on the providers of time to give a
clear indication of what time_t should try to count.

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

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