Some argue that 13 sign astrology is the right way and everyone else is doing it wrong. They'll say that any astrologer with astronomical knowledge will realize 13 is the way to go
As a novice and idiot, I have no arguments against that but that 12 sign works for me, helps me, and is something I find relation in. My argument would be that if it helps, it's 'right'
But I am interested in looking deeper and I know the people here aren't short of astronomical proficiency
So what are some valid arguments against those claims?
The biggest argument is that astrology really has little or nothing to do with the constellations of the zodiac.It has to do with the ecliptic, and the relationships of the earth and the planets. The constellations are just landmarks on that path that we have used to name the 12 equal territories on the path. They just happened to be on the path when astrology was formulated, but they are not the path itself. And just as a landmark might disappear on earthly path over time, the actual longitude and latitude of the path remains the same. For instance, down the road from my home is a farm called GreenWillow Farm. It got that name for huge willow tress that at one time lined the road at its gate. Those trees have died and are now gone but we still call it GreenWillow Farm. Its still the same place.
Astrology is an expression of the sacred geometry that unifies reality. That geometry has not changed because the constellations have appeared to have shifted some what over the eons. Aries is the first 30 degrees of the zodiac, no matter what constellations happens to move into the sky behind this first 30 degrees of the ecliptic. It's first because it happens when the equinox occurs to mark a beginning point. Twelve has always been a special number in metaphysics because of its unique ability to be divided equally by 2, 3, 4, and 6. and because it is made up of 1 and 2 - 1 implies wholeness or unity and two implies duality or opposition etc. there is much written about the symbolism of these numbers if you care to research that.
It is obvious that the constellations of Aries or Cancer etc. did not get their names because the looked like a Ram and a Crab. Aries probably got its name because ancients people noticed that those born in that first 30 degree segment behaved like a Ram. And those born under the fourth 30 degree segment of the great circle acted like a crab. A different constellation could appear in the first 30 degrees of the ecliptic tomorrow and it would change astrology not one bit. If the stars in one of the smaller constellations suddenly burnt out and the constellation disappeared it would not change astrology one bit.We would still have 12 equal divisions along the ecliptic where we see the planets , Sun and Moon travel.
So the belief that astrology works because some named constellation that is sitting way behind the ecliptic has some metaphysical power by virtue of what it happens to be named is a notion held by people who usually know very little about a astrology. It's probably not the case - In fact I am certain it is not.
So that a 13th constellation has entered the backdrop behind the ecliptic due to the precession of the equinoxes has changed nothing unless you believe it is a handful of constellations that are the underlying unifying metaphysical substrate of the cosmos and not the primary mathematical and geometric relationships and essences that are expressed in numbers.