Re: Compute Date Duration

On 10/18/05, Leif Svalgaard <lsvalgaard@xxxxxxxxx> wrote:
> On 10/18/05, Simon Coulter <shc@xxxxxxxxxxxxxxxxx> wrote:
> > Scaliger numbers go back to sometime in 4000BC (I think) so perhaps
> > defining the correct calendar might cause the MI instructions to handle
> > earlier dates but I suspect that might not be the case. What business
> > reason is there for dealing with such early dates?
>
> Astronomers even today use the "Julian day" count to avoid confusion
> with changing calendars. The Julian day count is the number of days
> since noon (GMT) on January 1, -4712, i.e., January 1, 4713 BC. This
> scheme was proposed by Julius J. Scaliger  in 1583 (so has nothing
> to do with Julius Caesar).
>

That 1st January, 4713 BC is on the Julian calendar, BTW. The one
that had a leap year every 4th year. To get an idea of the mess consider
the fact that in 46 BC J. Caesar instituted his calendar reform, but the
priests in charge of the calendar screwed up and decreed every 3rd year
to be a leap year. The error was discovered in 9 BC, and no more leap
years were added until 8 AD to bring the calendar back on track, so
4 AD was not a leap year. Leap years were: 45 BC, 42 BC, 39 BC, 36 BC,
33 BC, 30 BC, 27 BC, 24 BC, 21 BC, 18 BC, 15 BC, 12 BC, 9 BC, 8 AD,
12 AD, etc. I know of no calendar routines that takes this into effect.
It is unlikely that the AS/400 routines do this correctly. but I have not
tried.


--
Leif
leif@xxxxxxxx