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By David McCann

Trying out house systems other than Placidus is often seen as a difficult business. In fact, it is possible to set up houses for most systems using Placidian tables, such as Raphael's Tables of Houses for Northern Latitudes. The secret is that every cusp is the same as the Ascendant at a different time and latitude. Thus in any chart, the Midheaven is the same as the Ascendant in a chart cast 6 hours earlier at the equator. To find each intermediate cusp we must first know the time and latitude for which the Ascendant has the same position.

For the Regiomontanus system, the times are given by the following table:

 House Cusp Time to Find Ascendant 11th house 4 hours earlier 12th house 2 hours earlier 2nd house 2 hours later 3rd house 4 hours later

The latitudes are found from the table below.

For example: if the chart is to be cast for latitude 51°30'N, we find that figure in the first column. There are two columns: one headed 11th/3rd house, and the other 12th/2nd house. The figure in the first of these for 51°30'N is 32°09', meaning that the cusps for the 11th and 3rd house are found from the ascendant at that latitude. Similarly, the latitude in the 2nd column, 47°26', will be used for the cusps of the 12th and 2nd houses. Thus to find the cusps for London at 13 hrs local sidereal time:

 11th cusp Asc. at 32°09' 13hrs - 4hrs = 9hrs 8° Scorpio 12th cusp Asc. at 47°26' 13hrs - 2hrs = 11hrs 25° Scorpio 2nd cusp Asc. at 47°26' 13hrs + 2hrs = 15hrs 17° Capricorn 3rd cusp Asc. at 32°09' 13hrs + 4hrs = 17hrs 8° Pisces

 Table of Latitudes Lat. 11th/3rd house 12th/2nd house 5° 2°30' 4°20' 10° 5°02' 8°41' 15° 7°38' 13°04' 20° 10°19' 17°30' 25° 13°07' 21°59' 30° 16°06' 26°34' 35° 19°18' 31°14' 40° 22°46' 36°00' 45° 26°34' 40°54' 50° 30°47' 45°54' 51° 31°42' 46°55' 51°30' 32°09' 47°26' 52° 32°37' 47°57' 53° 33°34' 48°58' 54° 34°32' 50°00' 55° 35°32' 51°03' 56° 36°33' 52°05' 57° 37°36' 53°08' 58° 38°40' 54°11' 59° 39°46' 55°15' 60° 40°54' 56°19' 65° 47°00' 61°42'

David McCann, who lives in London, is an expert on the history and philosophy of astrology. His articles have been published in many international journals of astrology and he was a regular contributor to the Traditional Astrologer magazine, where this article first appeared.