Occult Origins of Technology · 6/7 · c. 150 – 1770 CE

Astrological Tables → Navigation

Horoscopes paid for the stars. To cast a horoscope you must know exactly where the planets were at a given moment, from a given place. Centuries of people wanting that produced the tables, the instruments and the arithmetic that later let a ship work out where it was — which is the same problem, asked at sea.

REVISED 2026-07-24 · 10 THE CLAIMS, LABELLED

1. CL-01
   Ptolemy wrote both the Almagest, which computes planetary positions, and the Tetrabiblos, which interprets them. In the second century these were two halves of one subject, not two subjects.Ptolemy, Almagest (c. 150) and Tetrabiblos (c. 150); Evans, The History and Practice of Ancient Astronomy (1998).
   Documented
2. CL-02
   The Islamic zīj tradition produced hundreds of observationally corrected planetary tables between the ninth and fifteenth centuries, and horoscopic practice was among their principal uses.King & Samsó, “Astronomical Handbooks and Tables from the Islamic World”, Suhayl 2 (2001).
   Documented
3. CL-03
   The Alfonsine tables, compiled at Toledo in the 1270s, remained the European standard for computing planetary positions for roughly three centuries.Chabás & Goldstein, The Alfonsine Tables of Toledo (2003).
   Documented
4. CL-04
   Regiomontanus printed his Ephemerides in 1474, sold largely to astrologers and physicians, and the same volumes were carried aboard ship.Zinner, Regiomontanus: His Life and Work (1990 trans.); the Ephemerides ran 1475–1506.
   Documented
5. CL-05
   Columbus used a predicted lunar eclipse from Regiomontanus' tables to intimidate Jamaican islanders into resupplying his crew in February 1504.Ferdinand Columbus, Historie; corroborated by the eclipse's computed date. A table sold for horoscopes, used as a weapon.
   Documented
6. CL-06
   The Nautical Almanac, first published for 1767, tabulated lunar distances so a navigator could determine Greenwich time — and therefore longitude — from the sky alone.Maskelyne, The Nautical Almanac and Astronomical Ephemeris for the Year 1767; it has appeared annually ever since.
   Documented
7. CL-07
   The astrolabe measures the altitude of a body above the horizon, and the same measurement serves to cast a horoscope and to find latitude.The instrument does not know what the reading is for. Its mariner's variant strips the astrological plates and keeps the altitude scale.
   Technique
8. CL-08
   Harrison's marine chronometer solved the same longitude problem mechanically, in direct competition with the lunar-distance method.Both were pursued for the Board of Longitude's prize; ships carried both for decades, checking one against the other. The clock owes nothing to astrology — which is the point of listing it here.
   Coexistence
9. CL-09
   Astronomy had to free itself from astrology before it could produce anything useful.The order runs the other way. The demand for horoscopes is what funded centuries of position-measuring, and the tables that made navigation possible were compiled and sold inside that demand. Kepler cast horoscopes for money while writing the laws of planetary motion.
   Myth
10. CL-10
    Ancient astronomers were really doing science and merely tolerated the astrology.A modern division projected backwards. Ptolemy wrote both books; the separation of the two subjects is a seventeenth- and eighteenth-century development, and reading it into antiquity misdescribes what these people thought they were doing.
    Reinterpretation