Calculation Accuracy

All planetary positions are calculated using the Swiss Ephemeris™, which “is at least as accurate as the Astronomical Almanac, the standard planetary and lunar tables astronomers refer to.”

The core part of Swiss Ephemeris is a compression of the JPL-Ephemeris DE406, plus an extension of the time range to 10,800 years, from 2 Jan 5401 BC to 31 Dec 5399. As a guide, the accuracy of the standard planets around the current era is estimated to be as shown in the following table.

For a more detailed explanation of how the accuracy is estimated, see the Swiss Ephemeris website at http://www.astro.ch/swisseph/.

When Solar Fire calculates heliocentric positions, they are true dynamical positions, and have no corrections applied. Their geocentric positions are corrected for nutation and light time delay, and therefore correspond closely to the positions published in the "The American Ephemeris" (ACS), for example.