Southern Hemisphere Astrology is simply bent on finding meaning in what is in the sky. It pays homage to the signs, although it rotates them 180°, but recognises the background of fixed stars, and has been at pains to correlate them with the houses and constellations of the zodiac.
It has come to seem obvious to me that sidereal astrology, if recognising kinship of Sun, Moon and planets with fixed stars, must abandon an ecliptical perspective in favour of an equatorial one.
As you probably know, there are three main coordinate systems for locating objects in the sky for observation. Astronomers generally use equatorial and horizontal coordinates, and astrologers generally use ecliptical coordinates.
To run through them briefly, horizontal coordinates, which we are most familiar with, specify azimuth—angle (0-360) from due north measured clockwise—and altitude—angle (0-90) with the horizon. This is a simple system, but it cannot divide the sky informatively when several constellations are stacked on top of each other in the east, for example.
Equatorial coordinates are a measure of an object’s position east of the Aries Point—our autumn equinox intersection of the planes of Earth’s rotation and orbit—along the celestial equator, and its angular distance from it, expressed as positive below or negative above, from our point of view.
Ecliptical coordinates likewise measure an object’s angle with the autumn equinox, but along the ecliptic, and its angular distance from that. This system is preferred by astrologers who simply need to know the angles between objects and their progress through the signs, but its use in correlating positions of planets and stars in constellations and houses is limited, as illustrated by the problem highlighted in the image below.
At the moment depicted, the Moon and Deneb Algedi straddle the meridian. The Moon has crossed, Deneb Algedi has not. The zodiac is slewed 21° west of north, and the longitude circle extending from the MC places the Moon in the third house and Deneb Algedi in the third. Can’t have it!
Making the cusp of the fourth house (or the tenth in the upside-down convention) the intersection of ecliptic and meridian makes a lot of sense to me, but the exercise seems invalid unless the meridian is the fourth cusp for my sky and everything in it.
There is a way of retaining both the simplicity of the ecliptical system of location comparison and mid-heaven as cusp of the house of stature, which is to transfer the status of the meridian to the highest point of the zodiac arch, but thereby cast astrology adrift from an essential anchor, the hours of the day.
Stickler for geographical exactitude I may be, but geometrical exactitude just does not work when projected onto the real sky in the real world.
Therefore Southern Hemisphere Astrology now works in hour circles. Equal divisions of the equator form the cusps of houses, and the same equal divisions of the ecliptic form the equatorial boundaries of the constellations.
And you will see from the snapshot below of the Moon’s transit that mid-zodiac has now lost its symmetry with its ends, but the Moon is still in opposition to Venus and Jupiter, which are still in conjunction! Cardinals are still opposite each other, as are the vertices. More importantly, equatorial positions put the Moon west of the MC; ecliptical positions do not.