House Tables

Definition

House tables are printed reference tables that convert sidereal time and geographic latitude into the zodiacal positions of house cusps — most importantly the Ascendant and Midheaven. Before computational astrology, a practitioner cast a chart by looking up the rising and culminating degrees for the birth time in pre-computed house tables for the relevant latitude, then arranging the remaining cusps according to the chosen house system. The genre is auxiliary to ephemerides: ephemerides give planetary longitudes by date, house tables give the angles by sidereal time.

In Tradition

From the late medieval period through the late 20th century, house tables and ephemerides were the practical computational scaffolding of Western astrological practice — the printed apparatus that made chart-casting tractable before software-based calculation. Holden documents the genre via specific 17th-century compilers and frames the period dependence plainly: 'in Cardan's time any calculation at all was tedious and astrologers were largely dependent upon printed tables of houses and auxiliary tables.'

In Practice

Practitioners working in the pre-software era used house tables in the following pattern: convert local mean time of birth to sidereal time using the ephemeris's daily sidereal-time column, look up the converted sidereal time in the house tables for the geographic latitude of birth, and read off the Ascendant degree, Midheaven degree, and intermediate cusps for the chosen house system. Different house systems require different tables: Regiomontanus tables from Müller's 1490 edition supplanted the older Alchabitius tables and dominated through the late 19th century, when Placidus tables became standard for English-language practice. House tables are typically published for specific latitudes or in latitude bands, with interpolation required for intermediate latitudes. Modern software has largely retired the printed-tables workflow, but tables remain available in print and online as a verification aid for hand calculation and as a tangible record of the pre-software computational era. Argoli's *Ephemerides ab anno 1630 ad annum 1680* (Venice 1638) and *Exactissime coelestium motum ephemerides 1641-1700* (Padua 1648) are representative artefacts of the genre.

Historical Origin

Printed house tables developed in the early-modern European astrological-astronomical period alongside the broader printed-ephemeris genre. Holden documents Andrea Argoli (1570-1657), a student of Magini, as one of the principal 17th-century compilers, publishing house tables, auxiliary tables, and ephemerides covering 1620-1700. The pre-Argoli reliance is attested in Holden's note on Cardan's era: practitioners 'were largely dependent upon printed tables of houses and auxiliary tables' for any calculation at all. The genre continued in standard use through the late 20th century before software-based calculation displaced printed reference tables from routine practice.

Etymology

Origin: English. Meaning: Compound of 'house' (astrological house) + 'tables' (printed reference tables). The genre name designates the printed-reference auxiliary used to convert sidereal time and geographic latitude into the zodiacal positions of house cusps..

Further Reading

• James H. Holden, A History of Horoscopic Astrology