I, personally, don’t believe in the Equal House System for purposes of ‘normal’ astrology. (It is really good for harmonics when doing vibrational astrology, as harmonic charts are not ‘real’ charts but methods to see aspects between planets (say, 7th harmonic aspects) that we wouldn’t be able to see on an ordinary chart.
For my preference in normal natal charts (which is Placidus or Koch), I wrote a paper on it with that justification that I’ll excerpt from at the bottom of this article.
For Placidus or Koch, if we stick to the Northern Hemisphere, there are several things we know. The further away from the equator we go, the more the house system is skewed.
Secondly, the midheaven is most likely to be square the ascendant (and thus three signs away, the closer the ascendant is to either the Pisces/Aries cusp, or the Virgo/Libra cusp. The midheaven is most likely to be skewed the closer the ascendant is to the Gemini/Cancer cusp or the Sagittarius/Capricorn cusp. It is on a continuum from the point we think of as the equinox to the point we think of as the solstice.
When we get up into the northern latitudes, even having an Aries rising doesn’t help you:
I was always interested in this topic and have been aware of it for years, long before David Cochrane taught it in our Vibrational Astrology program. Maybe it was a way for me to brag about knowing something that most intermediate astrologers didn’t know; maybe it had to do with my fascination with this phenomenon or maybe it was an intellectual exercise.
The astrology students I studied with are now aware of this phenomenon. It was covered.
If we relocate this chart to Barrow, here’s what we get.
All of these chart wheels are done through TimePassages, an astrological charting service that I love and use a lot (it is lovely to look at), but unfortunately they keep the house numbers in the same place and not congruent with the actual houses, causing confusion. In this case, I’m not even sure what houses are where, but there appear to be only eight. As in the caption, the Midheaven appears to be below the horizon.
There are many excellent articles and videos that try to address this phenomenon. This one illustrates the dilemma. David Cochrane has some great videos — here and here. The second video he produced at about the time he was teaching this subject to us; it’s more recent and admittedly I haven’t watched all of it, but he’s discussing the influence of the vertex as becoming more influential the further away from the equator, until the ascendant disappears and the vertex applies instead. It’s a really innovative way to think about the problem.
But I want to try to parse out why this all happens.
We know that the Earth tilts 23 degrees and 27 minutes on its axis. That North pole is always tilted the same way, but the earth’s revolution around the sun causes the pole to tilt either toward the sun or away from it (or, at the equinoxes, sideways from it).
This is the reason that in the Northern Hemisphere, the most common ascendants are Leo, Virgo, Libra, and Scorpio and the least common ascendants are Aquarius, Pisces, Aries, and Taurus. In the Southern Hemisphere, it’s the opposite. The pole tilting in the same direction makes the particular ascendants more common.
For more explanation, the rising sign is the point on the horizon where the Sun would be rising that day (more or less). As the earth rotates, the signs do not process at an equal rate. If you imagine being north of the Arctic Circle, certain ascendants simply are not accessed, as the Arctic Circle “contains” locations away from certain ascending signs (at the very least, much of Aries and Pisces). The midheaven is not affected.
I’ll excerpt from the paper I mentioned. My paper was a justification for specific house systems, like Placidus or Koch.
At first I was impressed with Campanus, with its division of the celestial sphere. (Does the above illustration indicate that it’s Campanus? I can’t tell.) I realized that its celestial sphere divisions were not equal in area, but only in linear distance, and I found it to be a very irritating system. In fact almost always the 9th and 10th house are very small and the 7th and 12th house are very large. This does not seem ‘natural,’ and I can prove that Placidus takes into account important things that Campanus does not.
Let’s pretend we are at the Summer Solstice at about 40 degrees North (actually, as I write this it is June 24 and I am in Denver, so we’re pretty close!). At this time of year, the length of the day is 15 hours and the length of the night is about 9 hours. Yet the Ascendant and Descendant are opposite signs. What that means is that in 15 hours of daytime six houses move 180 degrees, or an average of 12 degrees per hour, but in 9 hours of nighttime, six houses move 180 degrees, or an average of 20 degrees per hour. During other times of the year there is similar skewing but the skewing is not centered on the ascendant and descendant; it is some other set of oppositions in the chart wheel. The house system we use should be the house system that is most congruent with this reality.
I can only conclude that the quadrant house systems that divide the semi-diurnal arc into three equal pieces, in terms of distance on the arc itself, are the only house systems that can accurately account for this reality. Your video graphically delineating Steffi Graf’s chart at birth time (which is near sunrise in this case, so her Sun is conjunct her ascendant):
and; then her chart projected to noon (or, the highest point in the day), which, given that she was also born so close to the Summer Solstice is roughly 8 hours later:
serves to further illustrate the semi-diurnal arc’s accuracy at accounting for the reality of the skewed projection of the ecliptic plane in the sky.
This is more technical than I usually write — or at least my explanation for why charts get skewed the further away from the equator you go.