House (astrology) - Systems of House Division

Systems of House Division

There are many systems of house division. In most the ecliptic is divided into houses and the ascendant (eastern horizon) marks the cusp, or beginning, of the first house, and the descendant (western horizon) marks the cusp of the seventh house. Many systems of house division called quadrant house systems also use the midheaven (medium coeli) as the cusp of the tenth house and the nadir (imum coeli) as the cusp of the fourth house. Some house systems divide the celestial equator and the prime vertical instead of the ecliptic.

The earliest systems (whole sign and equal house) linked the houses to the signs of the zodiac. The equal house system defines houses as 30-degree sectors of the ecliptic, so that the cusp of each house falls on the same degree of each zodiac sign. One outcome of this is that a varying angle occurs between the ascendant and midheaven in higher latitudes. Attempts to reconcile the concept of "quadrants" with the varying angle between midheaven and ascendant lead to more complicated house systems. These became more relevant as astrology spread from subtropical regions to higher latitudes.

Goals for a house system include ease of computation; agreement with the "quadrant" concept (ascendant on the first house cusp, nadir on the fourth, descendant on the seventh, and midheaven on the tenth); defined and meaningful behaviour in the polar regions; acceptable handling of heavenly bodies of high latitude (a distinct problem from high-latitude locations on the Earth's surface); and symbolic value. It is impossible for any system to satisfy all the criteria completely, so each one represents a different compromise. The extremely popular Placidus and Koch systems, in particular, can generate undefined results in the polar circles. Research and debate on the merits of different house systems is ongoing.