How We Calculate

Swiss Ephemeris is a high-precision astronomical calculation library developed by Astrodienst AG in Zurich. It is based on NASA JPL DE441 planetary and lunar ephemeris — the same data used by space agencies and observatories.

The library delivers sub-arcsecond accuracy for planetary positions across a 13,000-year range (5400 BCE to 7800 CE). Every chart and transit on OmenMe is computed in real time using this engine — we never use pre-computed tables or approximations.

OmenMe uses the tropical zodiac, where the first degree of Aries begins at the vernal equinox. This is the standard system in Western astrology and aligns zodiac signs with the seasons rather than with the current positions of the constellations.

The sidereal zodiac, used primarily in Vedic (Jyotish) astrology, accounts for the precession of the equinoxes and places signs approximately 24 degrees earlier. We chose tropical because it is the most widely used system in Western practice and the one most readers are familiar with.

We use the Placidus house system — the most common house division method in Western astrology. Placidus divides the ecliptic based on the time it takes each degree to travel from the horizon to the meridian.

House positions require an accurate birth time. If birth time is unknown, we use a noon default and clearly indicate that house and rising sign data may be imprecise.

After Swiss Ephemeris computes the raw astronomical data — planet positions, aspects, house placements — our AI models interpret the results in the context of your personal natal chart.

The AI does not replace astronomy. It translates precise calculations into readable, personalized insights. Every AI interpretation references the specific planetary configuration that drives it, so you can always trace the reading back to real celestial data.

Horoscopes are regenerated daily with fresh transit data. Weekly and monthly readings are updated on schedule. The lunar calendar updates each month. Transit event detection runs on an hourly cache to capture ingresses, exact aspects, and retrogrades in near real-time.

Swiss Ephemeris is open source software. You can verify any calculation we produce by running the same ephemeris with the same inputs. This is a deliberate transparency choice — our calculations are auditable.