Hi Roger,

True; Find_Orb will interpret "14 jan 333 BC" (the way an historian
would write the date) as equivalent to "14 Jan -332" (astronomical
convention). So it can accept _input_ dates in either form.

Any _output_ in ephemerides, orbital elements, etc. will be in the
astronomical convention only. So ephemerides (from Find_Orb, and I'd
wager from JPL's Horizons and others) _will_ show a "year zero".

Another little 'gotcha': dates before 1582 October 4 are assumed to
be in the Julian calendar; dates after that are assumed Gregorian.
Using the JD values, which don't have these weird calendar conversion
and BC-versus-negative-year issues, is an excellent idea...

-- Bill

On 10/17/2013 10:50 AM, Roger W. Sinnott wrote:
>
>
> Alessandro,
>
> I don’t know what conventions are used by various online databases, but in standard chronological practice,
>
> 99 BC is the year -98 (not -99).