[H-GEN] Leap second?

Martin Pool mbp at pharos.com.au
Thu Jan 1 18:57:05 EST 1998


On Thu, 1 Jan 1998, Chris Pascoe wrote:

> I'm curious as to whether anyone noticed what appeared to be a leap second
> today?

That's why I feel so tired today! :-)

> I got (roughly) this on several machines running xntpd today..  which
> would seem to correspond to the skipping of a second at Midnight GMT.  I
> hadn't seen anything about it coming up (not that I've read much lately).

The only language I know of with built-in leap second support
(std-disclaimers) is at

  http://www.javasoft.com/products/jdk/1.1/docs/api/java.util.Date.html

and I quote:

% Although the Date class is intended to reflect coordinated universal
% time (UTC), it may not do so exactly, depending on the host
% environment of the Java Virtual Machine. Nearly all modern operating
% systems assume that 1 day = 24 × 60 × 60 = 86400 seconds in all
% cases. In UTC, however, about once every year or two there is an extra
% second, called a "leap second." The leap second is always added as the
% last second of the day, and always on December 31 or June 30. For
% example, the last minute of the year 1995 was 61 seconds long, thanks
% to an added leap second.  Most computer clocks are not accurate enough
% to be able to reflect the leap-second distinction.
% 
% Some computer standards are defined in terms of Greenwich mean time
% (GMT), which is equivalent to universal time (UT). GMT is the "civil"
% name for the standard; UT is the "scientific" name for the same
% standard. The distinction between UTC and UT is that UTC is based on
% an atomic clock and UT is based on astronomical observations, which
% for all practical purposes is an invisibly fine hair to split. Because
% the earth's rotation is not uniform (it slows down and speeds up in
% complicated ways), UT does not always flow uniformly. Leap seconds are
% introduced as needed into UTC so as to keep UTC within 0.9 seconds of
% UT1, which is a version of UT with certain corrections applied.  There
% are other time and date systems as well; for example, the time scale
% used by the satellite-based global positioning system (GPS) is
% synchronized to UTC but is not adjusted for leap seconds. An
% interesting source of further information is the U.S. Naval
% Observatory, particularly the Directorate of Time at:
% 
%        http://tycho.usno.navy.mil 

I couldn't find a timetable of leap seconds.

--
Martin Pool, Pharos

The only "intuitive" interface is the nipple. After that, it's all learned.
(Bruce Ediger, bediger at teal.csn.org, in comp.os.linux.misc, on X interfaces.)

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