Calculation Accuracy: ±0.001 Arcsec Verified vs NASA JPL
Astronomical accuracy here is your maximum positional error of any planetary longitude reported by stars.expert. Our engine uses the Swiss Ephemeris by Dieter Koch and Alois Treindl at Astrodienst, a compressed reading of NASA JPL DE431 and DE441. End-to-end agreement against JPL Horizons stays within ±0.001 arcsecond using the IAU 2006 precession model and IAU 2000B nutation, the kind of rigor that Ptolemy and modern Hellenistic researchers like Chris Brennan would have demanded.
Our Precision Standards
Margin of error less than one thousandth of an arcsecond.
Precision to ten-thousandth of a degree.
Exact aspects calculated to the second.
Why Precision Matters
Ascendant Calculation
The Ascendant changes by 1 degree every 4 minutes. A few minutes error in birth time can completely alter the interpretation.
House Cusps
The exact position of cusps determines which house planets fall into, affecting the entire chart reading.
Planetary Transits
Precise calculations allow identifying the exact moment when a transit becomes active or perfects.