Method

Astronomical calculation

• Ephemeris: We calculate planetary positions with the open-source library astronomy-engine (MIT licence) as apparent geocentric ecliptic positions. Our engine is verified against reference values from the Swiss Ephemeris to arc-minute accuracy — with test cases ranging from the southern hemisphere to the historical double summer time of 1947.
• Zodiac: We use the tropical zodiac, as is customary in Western astrology.
• House system: The default is Placidus. Beyond ±66° latitude Placidus is mathematically undefined — there we switch to Whole Sign automatically and say so.
• Lunar nodes: We calculate the true (not the mean) lunar node.
• Time zones: We resolve historical time zones and daylight saving time via the IANA time zone database — including special cases such as the double summer time of 1947. For ambiguous times (clock changes) we ask instead of guessing.
• Aspects: Conjunction (orb 8°), opposition (8°), trine (7°), square (7°), sextile (5°); the Sun and Moon receive +2° of orb.

Data sources

The birthplace search is based on data from GeoNames (licence CC BY 4.0). We host this data ourselves — your input is not sent to external geo services.

The position of Chiron comes from a table we store ourselves, taken from the Horizons system of NASA/JPL (public domain), since our ephemeris library does not calculate asteroids. Here too, no input leaves our server.

Interpretation texts & use of AI

Our readings consist of two layers: editorially reviewed text blocks (for placements such as “Sun in Aries”) and a personal summary that is generated with AI assistance from the abstract properties of your chart. We send no names and no exact birth data to the AI system — only the calculated chart properties. All delivered texts, whether editorial or AI-assisted, are labelled accordingly.

Tarot birth cards

Tarot birth cards are not drawn but calculated from the date of birth. We follow the method of Mary K. Greer (Tarot Constellations, 1987; Who Are You in the Tarot?, 2011): month, day and full year are added up, and the digits of the sum are added together until a number from 1 to 22 remains. A two-digit card leads via its digit sum to a second one. 22 stands for the Fool; 19 is the only number that leads through three cards.

The Tarot School counts the date in four two-digit groups (for example 03 + 15 + 19 + 77). Both methods always lead to the same single-digit card; the two-digit one can differ — which is why we name the method used on every result page. The year card comes from the birth month, birth day and the year in question; it applies from birthday to birthday.

The numbering follows the tradition of Pamela Colman Smith (1909): Strength is 8, Justice is 11. The astrological attributions of the cards come from the Golden Dawn (Book T, 1888). We determine the Sun sign without a time of birth, for the whole calendar day in German time; if the Sun changes sign on that day, we name both.

The card images are reproductions of the original illustrations by Pamela Colman Smith from the first edition of 1909/1910. They are in the public domain; we do not use the later recoloured editions.

Card images: Pamela Colman Smith, 1909/1910, gemeinfrei

Numerology

We calculate according to the Pythagorean system as developed in the 20th century by L. Dow Balliett and Juno Jordan: A = 1 to I = 9, then J = 1 to R = 9 and S = 1 to Z = 8. Each part of the name and each part of the date of birth is first reduced to its digit sum on its own; then the results are added and reduced again until a number from 1 to 9 remains. The master numbers 11, 22 and 33 are kept; only the personal year is always reduced to 1 to 9.

Umlauts count as in German correspondence: ä as ae, ö as oe, ü as ue, ß as ss. Other accents are dropped (José counts as Jose). We treat Y as a consonant; the soul urge number comes from the vowels a, e, i, o, u, the personality number from the consonants. The basis is the birth name, because the tradition reads it as the starting point. The full calculation is shown on the result page and in the dossier.

BaZi (Four Pillars)

BaZi assigns to the year, month, day and hour of birth one pair each of a Heavenly Stem (10) and an Earthly Branch (12), together a cycle of 60. Year and month follow the Sun, not the calendar: the year begins at Lichun, when the Sun reaches 315° of ecliptic longitude, and each month with one of the twelve solar terms spaced 30° apart. We calculate these moments with astronomy-engine to the minute.

The day follows the unbroken cycle of 60, the hour the twelve double hours starting at 11 pm. We read both by true solar time at the place of birth: longitude and the equation of time shift the clock time, daylight saving time does not count. The day changes at midnight; the hour from 11 pm to midnight (“late Rat”) still belongs to the old day, but its stem already to the new one. Some schools let the day change as early as 11 pm — which is why other calculators may show a different day pillar for births in this hour.

If a birth falls close to a solar term, we show both possible pillars. Without a time of birth there is no hour pillar. The element distribution counts the eight visible characters without weighting and without rating them as “favourable” or “unfavourable”; we do not calculate the ten-year luck pillars, because they require the person's sex, which we deliberately do not ask for.

Astrocartography

Astrocartography (Jim Lewis, 1970s) asks for each planet where on Earth it stood exactly on one of the four angles at the moment of birth. We calculate in mundoδ

Sidereal time and planetary positions come from astronomy-engine, as for the birth chart. A place counts as “on a line” when the great-circle distance is below the radius of influence (default 1,000 km); proximity is shown, not weighted. We do not calculate local space lines in this version. Without a time of birth the angles are undefined, so there is no map.

Parans

A paran (Jim Lewis called them “crossings”; Bernadette Brady brought them back into practice as paranatellonta) occurs when two planets stand on an angle each at the same moment: one rises, say, while the other culminates. On the map this is where two lines cross at the moment of birth. Because the Earth’s rotation shifts every longitude equally, the simultaneity depends on geographic latitude only: once the condition “longitude of one line equals longitude of the other” holds at a latitude, the combination happens at the same time everywhere on that latitude during the day. A paran therefore applies to the whole circle of latitude through the crossing point, not just to the point itself.

We check every pair of planets in the combinations horizon with meridian (rising or setting with culminating or anti-culminating) and horizon with horizon; two meridian lines never cross. The latitudes are found numerically and refined by bisection, geocentric, in mundo and without refraction like the lines. A place counts as “in the paran” when its distance in latitude from the circle is within the orb (default ±1°, adjustable under “Advanced”; 1° of latitude is about 111 km). Parans with fixed stars are described in the next section.

Fixed-star parans

In “Brady’s Book of Fixed Stars” (1998), Bernadette Brady links the planets to stars not by zodiac degree but through parans: a star counts when, during the day, it stands on an angle at the same moment as a planet. We use her list of 64 objects: 60 stars and four star clusters (Aculeus = M6, Acumen = M7, Capulus = h Persei/NGC 869, Facies = M22). Stars have no lines of their own on the map; they only appear as a planet’s partner, in the same twelve combinations of horizon and meridian as the planet parans.

The star positions come from the Yale Bright Star Catalogue, 5th edition (Hoffleit & Warren 1991, CDS catalogue V/50); those of the four clusters from the Messier and NGC catalogues. For the date of birth we carry the J2000 catalogue position forward with the proper motion and apply precession and nutation (astronomy-engine); compared with the IAU SOFA reference library, the positions of all 64 objects for 1900, 1985 and 2050 differ by at most 0.05″. We leave out annual aberration and parallax, which lie far below what matters for paran latitudes. As with the planet parans, the latitudes are found numerically, geocentric and without refraction; stars close to the pole do not rise or set at high latitudes and give only meridian parans there.

Because 64 stars and ten planets give about 3,500 parans per chart, we never show the full list, only the parans within the orb of the place being checked and of the birth latitude. The default orb is ±0.25° of latitude (about 28 km), tighter than for planet parans: on sample charts it gave 5 to 13 stars per place, ±0.5° already 9 to 26 and ±1° 17 to 49 — too many to stay meaningful. Under “Advanced” the orb can be widened to ±0.5° or ±1°. The star texts are our own wording; we do not reproduce Brady’s interpretations.

Putting it in perspective

Astrology is not a science, and we do not claim that it is. Geburtshimmel understands horoscopes as an invitation to self-reflection — a mirror for your own thoughts, not a prediction or life advice. For medical, legal or financial questions, please turn to the appropriate professionals.