FreeBSD handles leapsecond correctly

Carlos Amengual listas at
Tue Jan 3 16:24:30 PST 2006

John-Mark Gurney wrote:
> Having talked with a sextant user... leap seconds don't matter to
> sextant users...  They have a book of times and possitions, and the
> book is only good for a year or two... so needs to be reprinted, and
> on reprints, they can take care of the leap second issue...

Those tables are valid for a year (you can use computer programs too). 
If you use software, you have to fix the software, and if you use tables 
then a new set of tables has to be produced, where the time argument is 
not Universal Time (as until now), but Dynamical Time (TDT), or maybe 
something in the middle: "Dynamical Time plus something".

> so, the only fix for a sextant is a new table of numbers...  don't
> forget the tables HAVE to be updated for precisely the reason leap
> seconds are inserted...

It is not only an update, it is a change in the tables themselves. And 
sidereal time would no longer be sidereal time.

The current nautical tables use UT and not TDT as time argument 
precisely to avoid confusing people with timescales. Astronomical tables 
already use TDT (except for sidereal time), which is the kind of 
timescale that you want (TDT is based on TAI).

Carlos Amengual

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