What's the Origin of the Porphyry House System?

In episode 313 astrologer Luís Ribeiro joins the show to explain the astronomy and mathematics underlying the calculation of the different forms of house division in western astrology. We begin with a historical timeline showing when some of the different forms of house division were introduced, who the earliest sources are that mention them, and the time periods in which they reached the peak of their popularity. Then we go into a detailed breakdown of the astronomy and mathematics underlying how some of the most popular forms of house division are calculated. We focus in particular on the rationale for whole sign houses, equal houses, Porphyry houses, Alcabitius, Campanus, Regiomantanus, and Placidus. Our goal was not necessarily to advocate for any one system or talk about which was better to use in practice, but instead to help astrologers understand how the cusps are divided according to each approach. Towards the end of the episode we have a section talking about an astronomical instrument called an astrolabe, and showing how medieval astrologers used it in order to calculate the Ascendant, Midheaven, and other intermediate house cusps. For more info about Luis and his work visit: AcademyOfAstrology.eu This episode is available in both audio and video versions below, although we would encourage you to watch the video version because there are a lot of visuals. Timestamps Here are some timestamps for topics covered at different points in the episode: 00:00:00 Intro 00:01:00 Luis' book On the Heavenly Spheres 00:01:50 Luis' research on the astronomical rationale for house division 00:04:18 Understanding the basis of house division systems 00:05:04 Why astrology students should learn astronomy 00:07:20 Famous astrologers who were astronomers 00:08:40 Requirement to draw charts by hand in some schools 00:11:45 Different types of house systems 00:14:30 House division methods through time 00:17:38 Whole sign house system and its disappearance 00:20:55 Equal house system 00:29:50 Porphyry house system 00:33:57 Alcabitius house system 00:41:03 Works on house division systems 00:43:40 Whole sign not considered a house division by some academics 00:51:25 1959 German book that acknowledges whole sign houses 00:54:03 Campanus house system 00:57:00 Regiomontanus house system 01:05:50 Astro.com house system options 01:07:30 Solar Fire house system options 01:09:34 Placidus house system 01:14:26 Primary or diurnal movement 01:17:47 The ecliptic 01:22:27 Numbering of the houses 01:27:03 Dividing the circle 01:31:43 View of ecliptic from astronomy program 01:39:59 The meridian 01:44:50 Square chart example 01:46:40 3D diagram of the divisions 01:50:00 Zenith 01:53:00 Equator 01:54:05 Equator view from astronomy software 01:56:40 View from the north in the astronomy software 01:59:10 The zodiacal belt 02:00:43 2D diagram of the divisions 02:02:09 Whole sign method 02:04:48 Equal Houses method 02:08:12 Porphyry method 02:14:44 Alcabitius method 02:19:20 Campanus method 02:24:19 Regiomontanus method 02:28:32 Placidus method 02:38:39 Length of life technique and house division 02:54:30 Better documentation needed of house systems 02:55:45 Bias in academic research 02:57:42 Errors in descriptions of house systems 03:03:33 Different cusps 03:04:36 Astrolabe basics 03:14:10 Calculating houses with an astrolabe 03:26:18 Horary astrology and the astrolabe 03:29:00 Astrology boards 03:32:07 Astrology in academia 03:34:11 The challenge of different house systems 03:38:50 Different house systems for horary and natal 03:45:31 Revised version of Luis' book 03:46:00 Luis' website and Astro Project 03:46:43 Upcoming episode on Helena's work and new book 03:47:55 Closing remarks Watch the Video Version of This Episode Watch the video version of this episode on house division in astrology: https://www.youtube.com/watch?v=6ZmqOgdxkK4 - Transcript