Synastry is the art and science of comparing two birth charts to ascertain the energy flow between two individuals. Synastry is the astrology of relationships, and it reveals the level of compatibility between two people. Please don't confuse this with fortune-telling. Synastry will not tell you if you are "fated to be together." Any two people can choose to be together. Synastry shows if two unique individuals can be themselves and blend nicely together, or if being themselves causes the irritating grinding of mismatched gears.
Specifically, 3 things are compared:
- Elements – At the very least, the dominant element in each chart must flow smoothly with the other.
- House Overlays – "How you perceive each other." This is literally laying one birth chart over the other one, aligning them by zodiac sign degrees. First we note in which of your 12 Houses your partner's planets fall. Then we note in which of your partner's 12 Houses your planets fall.
- Synastry Aspects (also called Inter-aspects) – These are aspects formed from planets and angles in one chart to the planets and angles in the second chart. Here is the "nitty gritty" of a relationship. The dynamics between you is revealed by synastry aspects.
Nothing so profoundly affects our lives as contact with others, so this subject should be entered into with compassion and a commitment to thoroughness. If you rush the process of synastry, you will make erroneous judgments about something so serious. It is too easy and common for people to compare just 1 or 2 synastry aspects and assume they have the entire relationship mapped out. This is usually a huge mistake. Do not bother with synastry if you will not take the time to consider all parts. A real relationship is always at stake.
The scientific part of synastry is that all aspects, house cusps, planets, points, and angles are calculated mathematically. In this sense, synastry (and all astrology) is mathematically precise. Allowable orbs for synastry aspects range according to the preference of the astrologer. Keep in mind, we exist in a universal energy field in which an energy influence increases as it comes near us or decreases as it departs. It doesn't just appear or disappear. So we must be flexible with allowable orbs.
Then the art of synastry is to paint a picture of this energy field that is erected between the two birth charts. Please don't attempt to do this without some intermediate astrological knowledge. Especially regarding your own relationships! 99% of the time, you will not be objective regarding your own relationship synastry unless you are experienced in astrology. Take time and learn as much as you can before making judgment calls regarding relationships.