This is part of my research on how house systems are calculated, which I began with “wtf is a house”. In this post I look at one chart drawn in multiple different house systems and hammer out the technical definition of Mc/Midheaven. I also begin to touch on the quadrants and sections of how a chart is divided.
Different historical lineages account for different house systems. Because of how easily charts can be calculated with computers, it seems that most younger contemporary astrologers pick one house system that we’re comfortable with, because of what we learned or who we are inspired by. We might never deviate from, or question it. Before computers, astrologers calculated charts by hand (goals).
In my journey to explore different house systems and their origins, it’s necessary for me to completely grasp how the Mc, or Midheaven is calculated. How the Mc is accounted for differentiates house systems. There are three original branches of house systems: whole sign, equal, and quadrant1.
Some house systems put the Mc on the 10th house cusp, others leave it floating in another house. The cusp is the line where the house— not always the zodiac sign— begins. In the whole sign house system, the cusp of a house is always where the zodiac sign begins:
In this whole sign house chart, the Mc floats in the 9th house. The Ic is the point exactly opposite, floating in the 3rd house. The Mc is 9º45’ Aries and the Ic is 9º45’ Libra, 180º opposite. The cusp of every whole sign house begins at 0º and contains the whole 30º of the zodiac sign (0º-29º), beginning with the sign of the ascendant, or rising sign, which is Leo in this chart. Whole sign houses have been used since antiquity, and are the oldest equal house system.
Placidus is the most common quadrant house system today. It’s usually the default that people don’t really deviate from unless they’re incredibly geeky. And then, maybe, they find their way back around to it, because they feel like having a natal 5th house moon is less intimidating than a 6th house moon. Placidus is an uneven quadrant house system.
In the Placidus chart above, drawn for the same exact time and location, there are no points indicating the ascendant (it would say As) or the midheaven (it would say Mc), because with this house system, the As and Mc are the cusps of the 1st and 10th houses, respectively. The Mc is still 9º45’ Aries in the Placidus chart, and is illustrated as the cusp of the 10th house.
Placidus seems incredibly complicated to calculate. The difference between Placidus and Reggoimontanus, another uneven quadrant house system, is that between a space based and a time based calculation2. They are two differing interpretations of Ptolemy. Was Ptolemy using semi-arcs or great circles? I’m not a mathematician, not now.
Regiomontanus is from the renaissance, and it is the quadrant chart system I like to use when drawing a horary chart. Horary astrology is the astrology of divining answers to questions. It is what was used for horary charts by Olivia Barclay in Horary Astrology Rediscovered and Dr. J. Lee Lehman in The Martial Art of Horary Astrology.
Regiomontanusis a quadrant house system that appears to be nearly identical to Placidus. Placidus is more common for birth charts, and Regiomontanus for horary3. Both Regiomontanus and Placidus use unequal house divisions between the angles.
This is a Porphyry chart, again for the same time. It is one of the house systems that the Co-Star app uses, and it is the oldest quadrant house system. It is similar to Placidus, in that the angles (As/Ds, Mc/Ic) are the cusps of the angular houses (1/4/7/10). The difference is that the houses between the angles, the quadrants, are all divided into equal parts. Houses are angular (1st, 4th, 7th, 10th), succeedent (2nd, 5th, 8th, 11th), and cadent (3rd, 6th, 9th, 12th).
The angular houses in every chart are points of emphasis, because they begin each quadrant of a chart. They can be thought of as the handles of a wheel, where it is turned. Equal and whole sign house systems have floating points to show the the degrees of the calculated angles, and quadrant house systems collapse those angles into the houses themselves.
The equal and whole sign house examples both show the Mc floating in the 9th house, which is a sensitive point describing the legacy of a chart, as well as the cusp of the 10th whole sign house, which I would consider a zodiacal midheaven. Ancient astrologers would primarily use whole sign houses, then overlay them with equal or quadrant houses in order to contextualize certain techniques. Quadrant houses became more popular during the Medieval and Renaissance traditions, when we all forgot about whole sign houses for some reason4.
Equal houses are as old as whole sign houses in origin, but instead of beginning at 0º of a zodiac sign, the houses begin at the degree of the As or Mc. Here is an equal house chart that begins with the As:
Like the whole sign chart, the Mc floats in the 9th house in the equal house chart. The Ac doesn’t need to be signified, because it is where the 1st house cusp begins. Every house is “equal”, but the degree of the house is the same as the As degree. In equal sign houses, the 10th house cusp is also considered to be the Mc, because it is 90 degrees from the Ac, or the nonagesimal5.
This is also an equal sign chart, but the 1st house begins with the degree of the Mc, which leads me to wonder— how is the Mc even calculated?
While the Ac or rising sign describes the body of the captain driving the boat, in astrology, the Mc represents their highest achievement. It is the highest calculated point between the meridian (a line that connects the celestial north and south poles) and the sun’s ecliptic (the path of earth’s orbit). It’s how one is most visible.
The meridian is a curved line that connects the celestial north and south poles, anywhere on earth. It passes through the north and south poles, as well as the zenith and nadir, which are the highest and lowest points in the sky, relative to location. The zenith is actually not the Mc, but is rather a determining factor6. The ecliptic is a projection of the earth’s orbit onto the celestial sphere7. It’s the shape of the earth orbiting the sun.
So, if you take the ecliptic and add it it to the meridian for a certain time of day, you get the Mc. It’s a lot more personal than simply the zenith, or the astronomical highest point above you in the sky, which is only locational. The Mc takes a moment in time into consideration, so it’s more personal.
Brennan, Chris. “Chapter 11: The Issue of House Division.” Hellenistic Astrology, 2017, p. 366.
“Placidus House System.” Placidus House System - Astrodienst Astrowiki, 44 Feb. 2021, www.astro.com/astrowiki/en/Placidus_House_System.
“Quadrant House Systems.” Quadrant House Systems - Astrodienst Astrowiki, 13 Jan. 2019, www.astro.com/astrowiki/en/Quadrant_House_Systems.
Brennan, Chris. “Chapter 11: The Issue of House Division.” Hellenistic Astrology, 2017, p. 370.
Brennan, Chris. “Chapter 11: The Issue of House Division.” Hellenistic Astrology, 2017, p. 367.