Most people are familiar with the concept of compatibility in astrology. "I'm an Aries, he's a Cancer; are we a good match?" Person A's astrological chart is then compared to Person B's chart to determine how easy or difficult it will be to get along, understand each other, and have great sex. Then much giggling or moaning commences upon looking at each chart overlaid on the other. Once a relationship is established, for better or worse, it can seem to take on a life of its own! What you and another person create together can sometimes be very different from your own natures or even what you'd imagined the two of you would be like together.

Anything that has a birth has a birth chart, be it dog, person, or country, relationships included. The composite chart is just that: the birth chart of a relationship.

With people, it's not usually difficult to tell when they are born. Even if no one noted the time of birth, or even the day, the moment of birth is typically clear, give or take a few minutes. Relationship birth dates, like countries, may seem more challenging on first thought. When did this relationship begin? The first date? When we became monogamous? When we said "I love you?"

Composite charts use the moment of the first meeting between two people as the relationship's birth. As long as two people are conscious of each other, even if it's just for the moment of introductions or hellos, and even if nothing comes of the meeting until much later, that moment is the birth of a relationship where astrology is concerned. Talk about premature commitment!

Obviously not every meeting results in a notable relationship. One could meet the President of the United States once and a composite chart could be drawn up from that meeting; it certainly doesn't mean you're going to exchange vows or anything else but a handshake! Like an instruction manual, it's only useful if you plan on actually using the, uh, equipment more than once or twice.

Technique: Creating a Composite Chart
Composite charts are based on a technique known as midpoints. A midpoint is defined just as it sounds: it's the midway point between two things (in this case, planets). Each planet in person A's chart would be compared to the same planet in person B's chart: Sun to Sun, Moon to Moon, and so on. If person A's Sun is at 22 degrees of Virgo, and person B's Sun is at 15 degrees of Capricorn, then the half-way point between these two bodies would be around 19 degrees of Scorpio.

Obviously, since the chart is a circle, there are two midpoints between each planet's placements. In the above example, the longer way around the circle from Virgo to Capricorn would land in Taurus. Composite technique uses the shortest midpoint between two planets.

The composite chart has its own houses as well. House cusps in a natal chart are calculated based on one's birth location on earth, but with two different birth locations of two different people creating two different ascendants and so on, the house cusp calculation for composite charts can be trickier. There are a couple of ways to calculate house cusps in composite charts:

1. Calculating the midpoints of each house cusp from each chart.
   This method calculates the composite house cusps just as with the composite planets, typically starting with the Ascendant (or Midheaven); if person A has Pisces Rising, and person B has Taurus Rising, then the composite chart probably has Aries Rising. Easy, right? And we all know that Taurus comes after Aries, so if the midway point between two people's Ascendants was found in Aries, we would tend to assume that the midway point of the second house cusp would naturally be somewhere in Taurus, and so on. However, that is not always the case with this method.
   
   If two people have their house cusps in the opposite signs of each other, the natural sign order may be disrupted when using this method to create the composite house cusps. It could happen that given the actual exact degree each person's house cusps land in, the shortest midway point might take us the opposite direction, putting the second house cusp in the prior example in Scorpio instead of Taurus, even though Scorpio never follows Aries in a chart. Astrologers who use this method may often just use the midpoint that lies in Taurus, even though it may be the longer, not the shorter, of the two possible midpoints, to enable the composite chart to retain natural sign order.
   
   
2. Calculating the house cusps according to the location of the first meeting.
   This method calculates the midpoint of each person's Ascendant (or Midheaven) just as above with the Aries Rising example, but from then on, instead of midpoints between each house cusp all around the chart, it uses the location of the couple's first meeting to calculate the rest of the houses starting from the composite Ascendant (or Midheaven). An entirely different way to calculate a composite chart is known as the Davison chart. With this technique, instead of using the midpoints between house cusps and planets, the midpoint between each person's birth date is used to create a chart. The benefit is that a real chart based on actual planetary positions sometime between when the two people were born is created. The detriment is that it's not as intertwined between the two people as the composite chart seems to be.

Interpreting the Composite Chart
The composite chart is considered to be the birth chart of the relationship. Like a person's natal chart, it represents the strengths, weaknesses, purposes, and challenges of the relationship. What does the relationship want? What does the relationship fear? What makes the relationship feel happy? Just like a natal chart, we can ask these questions of the composite chart. However, it is up to the two people in the relationship to find answers and create solutions to the questions and challenges that the composite chart presents. They will also need to decide whether what the relationship wants is good for them as individuals. When any two people are in a relationship they want to continue building and deepening, the composite chart serves as an excellent instruction manual.

Looking briefly at an example, above is the composite chart of two people in a deeply committed friendship. The wealth of Aries planets in the first house reveals that the core needs of this relationship revolve around developing Aries qualities: initiative, directness, impulsiveness, and passion. The first house shows that the relationship is very self-focused and needs that time and attention to feel that its needs come first. The tightest portion of these planets lies in the conjunction between the Sun, Moon, and Mercury, suggesting the high importance of forthright communication.

With Neptune in the eighth house and being the chart ruler with the Ascendant in Pisces, the relationship may not always be what it appears. There is a gentleness and lightheartedness that may belie the intensity of the bond. Pluto right on the descendant reveals that other people may seem to represent a great threat to the relationship but can also be greatly transformative, causing the relationship to grow in ways it might not otherwise. Uranus here also seems to indicate that this relationship may not reflect the standard rules for what a relationship is expected to be. This can be a good thing as the relationship develops and trusts its uniqueness so it can develop longevity, which is something the relationship ultimately is aiming for with the north node in the eleventh house of the future.

Naturally, it is best to consider the natal chart of each person thoroughly before assessing the composite chart. A brief vignette of chart highlights reveals that Person A likes a lot of time alone, has a deep sense of duty to protect their partner, yet has high, unrealized, and unspoken expectations of a partner. Person B entered the relationship with a tendency toward too much people pleasing and a difficulty asking for what they want and accepting support. This composite chart poses a challenge for them both, since Person A tended to avoid confrontation and didn't consciously realize their own expectations easily, and Person B never wanted to appear selfish or confrontational.

As these two people have refined their relationship, the necessity for honest communication and for each individual to stand up for themselves has become very apparent. They have risen to the challenge within the context of friendship and their bond has become seemingly unbreakable as a result, with direct and frequent communication being the cornerstone.

It should be noted that composite charts are a special breed based on midpoint theory, but they are not the only astrological method used to examine a relationship. Outside of midpoints, one can certainly look at the chart for a marriage, or the chart of the first meeting, by simply calculating these charts in the usual way, as if they were natal charts for people. As with almost everything in astrology, there are multiple points of view and they all have a technique to go along with them, so take your pick!