Information about Synastry and Composite Charts
The astrological technique of Zodiac chart comparison is called Synastry. Its most common application is to answer the inquiries of lovers, or others, in – or entering into -relationships. It tends to yield impressive results.

The natal (birth) chart of one person is superimposed onto the chart of the relative person in question. Naturally, knowing the exact birth dates, times and locations produces the most accurate results. However, birth dates and locations tend to suffice. Planets and points in one chart are calculated in aspect to the planets and points of the second chart. Signs, Ascendants, and Houses are interpreted relative to each other; thus the Synastry Chart is ultimately interpreted as a single chart between two people.


For example, if my natal Sun in Virgo falls in opposition to the potential partner’s Sun in Pisces, we could assume two things: Either opposites attract, which is likely, or opposites have zilch in common, which may be problematic. Consequently, a synthesis of both interpretations is probably appropriate.

In Synastry, traditionally, the most powerful harmonious Aspects involve Sextiles and Trines, while the most powerful inharmonious aspects are Squares and Oppositions; this is not unlike a singular natal chart. Inharmonious aspects don’t spell doom – variety is the spice of life – but, the question is, are the differences habitable? Can they be tolerated and dealt with proactively, or will they build walls and install wedges? Without harmonious aspects, though, there is no real basis for cooperation and understanding, and thus, likely no foundations for a relationship to form – let alone last.
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Synastry, then, helps an astrologer explain how, and what, causes happiness and conflict. It can help show resolution to conflict, and how to enhance naturally congruent inclinations.

The best place to start is by interpreting both charts independently. Each chart shows a person’s natural dispositions, in general and towards interpersonal relationships. I like to look at The Planets in the First House of a chart, because if there are Planets there, they describe a person’s outlook on life and how they view themselves. Then I like to look at The Planets in the Seventh House of the chart, because those show how they experience relationships, and what they expect from others.

If there are no Planets in those Houses, I look at the Ascendant and Descendant, the Signs of the First and Seventh Houses, and the ruling planets of those Houses. I look to see if there are other significant points or aspects relative to those locations. I figure whether there is a general positive or negative relationship between those Houses of each chart – if any. Finally, I look at the remaining Houses, Planets, and Aspects. Not all relationships are all things, to all people. The charts show this.

I also look to see if there are relevant Transits. Some transits of planets are short-term (Moon, Mercury, Venus and Mars) and may point to a flight of fancy. Others are longer-term (Jupiter and beyond), and may or may not be truly lasting.

Comparing information from one chart to another, and relating them by aspect, is time-consuming and mindful. It is revealing, satisfying and worthwhile to a sincere inquisitor, however.

Midpoints and The Composite Chart
A Composite Chart is created by calculating the midpoints of the points and Planets in each chart. The near-midpoint location is thus the location of the planet in the Composite Chart.

The Composite Chart is not the chart of a person – it’s the chart of the relationship between two people. Therefore, the attributes of the Signs and Houses of this chart apply to a situation. Interpreting a Composite Chart includes a variety of methods. It represents the meaning of the relationship, the purpose of it, and also the direction it’s likely to take.

The Composite Chart has an Ascendant – which is the mean calculation of the Ascendants of the two natal charts in question. The Composite Chart, therefore, has its own unique Houses and Sign placements.

For example, my Ascendant is at 24° Virgo, and my relationship partner has their Ascendant at 6° Gemini. This calculates to a Composite Ascendant at 0° Leo. This means that the relationship projects the qualities of Leo: Generous, proud, emotional, romantic, extroverted, vain, egotistical, courageous – etc.

The Composite Sun of this chart is calculated the same way. Continuing with the previous example, my Sun is at 18° Virgo, and my partner’s Sun is at 20° Sagittarius. The location of the Composite Sun is therefore at 4° Scorpio. The basic identity of the relationship is expressed through qualities of solar Scorpio. Further, the Composite Sun in this chart lands in the Fourth House of home, family, the Mother – etc.

This is highly appropriate, as the partner in question for this example is my daughter, who is herself a mother!

Recall that in the Synastry, my natal Sun in Virgo is almost exactly in Square to my daughter’s natal Sun in Sagittarius, suggestion tension and difficulty. This has certainly been true, as we are very different people. The Composite Sun shows how and where our tensions operate – at home, with our family, and they’re expressed in a Scorpionic way.

Our Leo Ascendant is almost in Square with our Scorpio Sun, indicating that we’re often uncomfortable with our differences. Leo Ascending makes our issues seem dramatic, while the Scorpio Sun would prefer to bury them.

Many of our differences have been mitigated by the Composite Sun’s location in the Fourth House, however, because our Fourth House is ruled by Libra/Venus: Love.  In our Composite Chart, Venus falls in the Fifth House of children and entertainment. Certainly, the arrival of my granddaughter tempered our tensions!

The remaining Planets and points for a Composite Chart are calculated the same way. Then the Aspects between them are calculated and interpreted.

Hence, while Synastry and Composite Charts are most frequently used to address romantic questions and issues, as my example very generally illustrates, they are not limited to romantic relationships. Business partners, siblings, friends – Synastry is an applicable practice for all types of liaisons.

Composite Chart Planets in the Houses                Composite Chart Planets in Aspect              Compatibility Analyzer