Re: Julian Dates package?

[Mike Stark <michael.e.stark@gsfc.nasa.gov>]

Jerry van Dijk wrote:
> 
> Jay Joiner <jjoiner@ibm.net> wrote in article
> <32CFFA13.5BF8@ibm.net>...
> 
> > I am interested in doing a Biorythm calculator in Ada and I need an
> Ada
> > package that can take the difference between two dates (birthdate and
> > today).

I suggest using package Calendar, since it provides subtraction operator
for two absolute times, yielding elapsed times.  To compute number of
days, create a birthdate and current date of type calendar.time, with
the seconds of day set to zero.  This will give you a (fixed point) 
number of seconds.  Divide that number by 86,400 and you now have
the number of days.

If you have any more questions, feel free to e-mail me.

> 
> I thought Julian dates were mainly used for astronomy and such ?
> 
> Jerry.

That is correct.  However, in the systems we use at Goddard's Flight
Dynamics Division we model times as seconds from a fixed reference date.
With spacecraft it is important to include leap seconds, because each 
leap second you neglect can translate to 7 or 8 kilometers of along 
track error in your orbit computation.  I don't think leap seconds 
matter much for a biorhythms program, though ;)

Mike