[LEAPSECS] (no subject)

Steve Allen sla at ucolick.org
Mon Dec 22 11:01:45 EST 2008

On Mon 2008-12-22T14:10:25 +0000, Tony Finch hath writ:

> The code to implement this has in fact already been written, 15 or more

> years ago, but no-one uses it because it breaks too much stuff.

I am aware of the interesting breakages that happened when
zoneinfo files were retroactively modified to be inconsistent
with POSIX. Clearly that change cannot be done for past
history. That's part of the point of this live javascript page

> example, there is a lot of time-handling code in the kernel, and because

> it does not link with the tzcode library the proposed architecture doesn't

> accommodate its requirements. There's also a lot of code which doesn't use

> the C tzcode for time handling, such as the Java runtime. There is a

> pervasive assumption in Unix that midnight UT is when t % 86400 == 0.

So if the broadcast time scale were to become TI then these operations
would be taking place at "atomic day midnight" instead of mean solar
day midnight. That's still a legitimate kind of day.

Are there actually serious technical problems (kindly ignore
bureaucratic ones about conformance with UTC) with that sort of thing?

The argument that "atomic time will drift by no more than a few
seconds from mean solar during this century has been used by those who
want to abandon leaps. In the presence of an internationally approved
atomic time scale I think that argument goes both ways. It doesn't
hurt anybody if certain technical operations drift a few seconds from
civil wall clock time.

It has become clear in the ITU process that a change to the nature of
the broadcast time scale cannot be decreed with less than a decade of
advance notice. That's enough time to fix a lot of software and throw
away a lot of hardware.

If getting leaps out of the broadcast time scale is the principal and
urgent *technical* goal then it might be far quicker to decide to
choose "TI" than to hope for the *political* goals involved in getting
the ITU to disregard the history and the words of the CGPM when they
recommended UTC as a form of mean solar time. Technicians can adapt
a lot faster than politicians.

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

More information about the LEAPSECS mailing list