How Genastro works

Positions come from the Swiss Ephemeris, an astronomical library used by professional astrology software. The Sun, Moon and planets are geocentric ecliptic longitudes of date. The North Node and Lilith are mean points. Houses are Placidus or Whole Sign, your choice, and Placidus falls back to Whole Sign near the polar circles where it is undefined. Tropical is the default; sidereal uses the Lahiri ayanamsa.

Your birth time is local clock time, and clocks have not always matched today’s. The calculator looks up the offset in force at your birthplace on your birth date, daylight saving included, from the IANA time-zone database, then converts to Universal Time. The chart page prints exactly what was applied. Records before 1970 are less certain for some regions, so for an early birth it is worth checking the offset against a document.

Places come from a GeoNames extract (CC BY 4.0), which supplies coordinates and the time-zone name. You can check any position against another ephemeris.

The same engine was run over 2,000,000 simulated birth moments, and each placement and combination was counted. “0.6% of charts” means that share of the simulated births had it; “1 in 150” is the same figure turned around. Ranks name their direction (“33rd rarest”) and are given as “about” where neighboring ranks differ by less than the simulation’s own sampling noise.

The limits, stated plainly:

• It is a simulation, not a census. Birth years are drawn from 1950 to 2024. The seasonal curve (about 4% above average births in late summer, below in winter) and the time-of-day curve are simple assumptions, not fitted to real birth records.
• Places are drawn in proportion to city population, not to births, so countries with different birth rates are not weighted by them.
• Slow planets describe generations, not orbits. Pluto in Scorpio is not rare: it is the 1984 to 1995 cohort.
• The simulation measures tropical placements. For a sidereal chart the site reports the rarity of your tropical signs and says so.
• Rarity is a count of how often something happens. It says nothing about what a placement means.

The method is also explained in the lesson How rare is a placement.

The interpretation text on the placement, compatibility, big-three and born-on pages (130 blocks so far, two traditions each) is written by an AI. Each block was then checked by an AI research review that compares the text with sources and records its notes and references. Both steps are labeled on every block, with the date of the review and the references.

No person has reviewed this text yet. The label never says otherwise, and a block would be marked differently if a person signed it off. The voice rules (every claim attributed to a named tradition, no predictions, no outcome promises) are in the editorial guide the blocks are written against. Where traditions disagree the page shows both and names no winner.

The numbers on those pages are computed, not written: they come from the engine and the simulation, not from the AI-written text.

• It does not predict. There are no forecasts, no daily horoscopes and no “this year” readings.
• It does not give health, legal, financial or relationship advice.
• It does not claim astrology is validated. A chart is a computed fact; a reading is what one tradition says about it. See what astrology can and cannot tell you.