When you and I speak, touch, share or breathe the same air, we affect each other.
Synastry captures the connections found in the way we relate to another person. It is the scaffolding on which relationships form. My planets touch your planets through aspects (the major ones being the Conjunction, Opposition, Square, Trine, and Sextile) and through that interaction comes an energy that is essential to human survival on a soul level and contributes to how we build nations and communities on a macro level.
This is my specialty - understanding the ways in which we affect each other through our relationships. My Mercury in Virgo loves to analyze and dissect and their are limitless variations on the synastric possibilities between two people, or a person and an entity, or between two entities. It is quite possibly one of the most profoundly useful tools you can use to figure out how to navigate all the personalities you will come across in this lifetime. And of course, to determine and understand romantic and sexual potential between two people.