How we calculate
Our Methodology
The science behind our astrology calculations
Swiss Ephemeris
Vista Astrology uses the Swiss Ephemeris, the gold standard for astronomical calculations in astrology. Developed by Astrodienst, it provides highly accurate planetary positions based on NASA's JPL ephemeris data.
Our calculations are precise to within arcseconds for all major planets, the Moon, and the Ascendant. We use the Placidus house system by default, the most widely used house system in Western astrology.
What We Calculate
Planetary Positions
Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto, and the North Node (Mean Node).
House Cusps
All 12 house cusps calculated using the Placidus system, with exact degree positions.
Aspects
Major aspects including conjunctions, oppositions, trines, squares, and sextiles with precise orbs.
Big Three
Your Sun sign, Moon sign, and Rising sign (Ascendant) — the core of your natal chart.
Accuracy & Precision
- Planetary longitudes accurate to within 0.01 arcseconds
- House cusps calculated to the nearest arcminute
- Aspect orbs calculated with 0.01 degree precision
- Timezone handling supports historical DST changes
- Coordinates accepted to 4 decimal places (≈11 meter precision)
Interpretation Framework
Our interpretations are based on classical Western astrology traditions, drawing from centuries of astrological knowledge. Each planet-sign combination has been carefully written to reflect the established meanings within the astrological community.
We distinguish between dignity states (Domicile, Exaltation, Detriment, Fall) to provide nuanced interpretations of how planets express themselves in different signs.
Data Sources
Astronomical Data: Swiss Ephemeris by Astrodienst AG, based on NASA JPL DE431 ephemeris. Planetary positions accurate to within 0.001 arcseconds for dates between 13000 BCE and 16000 CE.
City Database: GeoNames geographical database (geonames.org), providing coordinates and timezone data for 12 million+ cities worldwide under CC BY 4.0 license.
House System: Placidus house system (default), the most widely used system in Western astrology. Also supports Koch, Whole Sign, and Equal House systems.
Interpretation Content: Written by our editorial team based on classical astrological texts including Ptolemy's Tetrabiblos, William Lilly's Christian Astrology, and modern psychological astrology by Liz Greene and Stephen Arroyo.
Transparency Note
We believe in full transparency about how our charts are calculated. If you have questions about our methodology, calculations, or interpretations, please contact us. We're always happy to explain our approach.