This question from Keteki was so fundamental and so important that I’ve decided to answer it as a post. She writes:

Hello Dawn

I always had this doubt about composites.
Why is it that only the midpoint between similar planets are given importance?
When two people interact why is the sun/sun and moon/moon midpoints more important than say A’s sun and B’s moon?

There is something called composite sun and composite moon and their aspects are important and reveal something about the relationship. Doesn’t the midpoint between different planets and their aspects say anything. If so aren’t we missing a huge deal in not having a chart for all these midpoints?”

A very good question:  why do we just make up this chart of like midpoints–Sun/Sun, Venus/Venus/, Mars/Mars?  Why don’t we consider all midpoints, if midpoints are so important?  What makes this particular midpoint chart something different from just a list of midpoints?

First of all, astrologers do use midpoints between planets in synastry.  Certainly the Soli-Lunar, or Sun/Moon midpoint, is a famous hot spot for relationship, both within and between charts  (see my articles on the Soli-Lunar Midpoint).  We all have our favorites; Venus/Mars might be a sexual boiling point, or Venus/Descendant might show us what we really desire in another.  But ultimately, the practical use of a standard midpoint is limited on its own, and only acquires meaning when we put it into the context of aspects.  If my Mars is square your Pluto, the midpoint of those two can be triggered by transiting planets or points, and then you can sit back and watch the fur fly.  If my Venus is Cancer is square your Uranus in Aries, the midpoint would reveal how inclined we were to flight or fascination.  If my Venus is trine your Uranus, the midpoint stimulation might lead us to adventure, rather than the divorce court.  But in all cases, I would feel my planet interacting with your planet in a highlighted way, and more detail would be supplied by the planet triggering the midpoint.

However, it’s still about two separate people interacting between two natal charts.  The composite chart is something else again.  In composite charts, there is a merging.  Our Suns can merge, our Moons can merge, but my Moon cannot merge with your Mars.  If you take the juice from one orange and mix it with the juice of another orange, you still have orange juice.  If you mix an orange with a mango, you have something new, not quite orange and not quite mango.  I’d be hard pressed to define what a merged Moon/Mars would actually be.  I would have to redefine every single aspect known to astrology.

Conceptually, what we are doing with a composite chart is creating an entirely new entity that has all the building blocks of any entity.  A thing unto itself, with its own life force.  It shouldn’t work, but it does.  I’ve seen it happen over and over and over again.  Couples often divorce or go through very rocky times when outer planets hit the Sun or the Ascendant of a composite.  Couples with Mars on the composite Ascendant tend to fight.  That’s just how they are together. Why?  Beats me.  But it comes down to the fact that all of astrology boils down to number, and numbers just work.  It’s as inevitable as 2 following 1.  Why2 should 2 follow 1 is another, deeper question, and has to do with the metaphysical basis of number–more on that another day.

Taking the midpoint of Sun/Sun, Moon/Moon etc. creates a unit, a third creature that is the essence of the merging of two souls.  There is a belief in Tantric philosophy that says that every time we have sex with another human being, we create a little ‘ghost.’ The composite chart IS that ghost.  It’s a map, too.  A map of our beginnings and endings, our ups and downs, our karma and our future together.  It contains what we were and what we are here to do.  Random midpoints define inter-action.  The composite chart, because of the structure it takes, is about much more.  It puts midpoint activity within a framework of being, so it can be read in a meaningful way.

Also, the natal and composite interpretations for the planets are virtually the same.  The Sun is the center, the life force of the composite chart.  It’s position shows us where our basic energy as a couple lies, and what enhances it and what impedes it.  The composite Moon shows the core of our emotional interaction, rooted in karma.  Our composite nodes tell us where we’ve been together and where we’re going.  It’s clear, it’s clean and it’s (fairly) easily interpreted, once it’s understood that the basic meanings only shift slightly from natal.

Anyone who has worked with composite charts in transit and progression knows their accuracy and their power.  When two people come together, the relationship has a purpose beyond the desires and reactions of the individuals participating in it.  This is what the composite charts reveal.  I’ve often seen cases where the individuals have terrible chart inter-dynamics, but get along famously.  Those are the ones who have lovely composite charts.  Sure, they irritate one another–but it doesn’t matter.  Together, they feel good, as if they can conquer the world.

Next time, the ever-important third quadrant:  houses seven through 9.