Calculating planetary aspects beyond conjunction with Jean Meeus library

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orbit123
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I am using the C library that comes with the book Astronomical Algorithms by Jean Meeus http://www.willbell.com/math/mc1.htm

This book and C library has a calculation for two planets Conjunction and Opposition but no other planet aspects. Does anyone know a method to find when two planets are a fixed degree apart such as 90 degrees, 120 degrees or any other degree?

The problem I have run into is that geocentric planets move through a retrograde and direct cycle. As an outer planet approaches the transition from retrograde to direct it is almost stationary at which time I can not calculate any accurate degree of separation. So I need a proven method to calculate the date-time of exact angular separate even when two planets are almost stationary.

Any advice would be appreciated.

Thanks
Patrick
 
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I think you're looking for a "Fundamental Solar System ephemeris".
I have never used such a thing, but there seems to be something useful at this site: http://ssd.jpl.nasa.gov/
 
The only way to do this exactly is to run a full-blown ephemeris of the Solar System and interpolate. Meeus gives you some handy formulae to approximate a number of interesting configurations, but these are indeed approximations boiled down from the full ephemera.