About & method
There are two halves to an astrology site. One half is arithmetic and can be got right or wrong. The other half is interpretation, and is neither. This page is about keeping them apart.
What is computed
Every position on this site is calculated, not tabulated from a lookup or invented. When you cast a chart, the following happens in your browser:
- Your moment is resolved. The birth date and clock time you give are interpreted in the time zone of the birthplace, using the historical rules in force there on that date. Wartime measures, abandoned daylight-saving experiments and mid-century zone changes are all honoured.
- Solar and lunar longitudes follow the low-precision series in Meeus' Astronomical Algorithms: the Sun to roughly a hundredth of a degree, the Moon — using the principal terms of the ELP theory — to a few tenths.
- Planetary positions come from Keplerian elements fitted to 1800–2050, propagated to your date, solved through Kepler's equation, and reduced from heliocentric to geocentric coordinates.
- The Ascendant and Midheaven are derived from Greenwich sidereal time, the obliquity of the ecliptic and the latitude of your birthplace. This is why a birth time and a real place matter, and why a chart without them is only half a chart.
- Retrograde motion is detected by comparing a body's longitude across a day, so the ℞ marks you see are the genuine article rather than a stored calendar.
What is interpreted
Everything else. The daily readings, the compatibility copy, the tarot meanings and the character sketches attached to placements are written by people, drawing on a tradition that has been arguing with itself for two thousand years. They are offered for reflection and entertainment. They are not predictions, and they are not advice — medical, financial, legal or otherwise.
Where the reasoning under a reading is structural, we say so. The compatibility page, for example, tells you the angular separation between two signs and what tradition makes of that angle, so you can disagree with the conclusion on its own terms.
Known limits
Pluto is not in the ephemeris, so signs that take it as a modern ruler are shown against their traditional ruler instead, labelled as such. Houses are equal from the Ascendant rather than Placidus; equal houses stay well-behaved at latitudes where quadrant systems fall apart. Positions are geocentric and apparent, without correction for nutation or aberration — both far below the resolution any horoscope needs. Dates outside 1800–2100 are refused rather than silently degraded.