What is synastry?
Synastry is the comparison of two birth charts. Each chart is calculated from one person's date, time and place of birth; synastry then measures the angles — the aspects — between the planets of the first chart and the planets of the second. A conjunction, trine or sextile marks an easy exchange between two points; a square or opposition marks friction that asks for work. House overlays add a second layer, showing which areas of life each chart activates in the other. Synastry describes the dynamic between two charts — not a verdict on a relationship, and not a prediction.
Sign compatibility compares two Sun signs and nothing else. Synastry compares two whole charts, so two people born under the same pair of Sun signs can produce completely different readings: the Moons, the angles and the house overlays are what separate them. That is also why an exact birth time matters here twice over — once for each chart.
WHAT THE RESULT CONTAINS
Three layers, one comparison.
The angle each planet in one chart makes to each planet in the other. Conjunctions, trines and sextiles mark easy exchange; squares and oppositions mark friction. Every contact carries its own orb — the distance in degrees from exact.
Which house of one chart each of the other's planets falls into. The same planet activates a completely different area — money, home, intimacy or career — depending on where it lands, which is why an exact birth time is required twice.
An overall score out of 100 and six category scores — emotional, intellectual, physical, spiritual, growth and karmic — weighted from the contacts above by the calculation engine.
Synastry is not a verdict. Challenging aspects do not say a relationship will fail; they say which subject asks for deliberate work. The numbers describe geometry between two charts, nothing more.
Synastry at a glance
| Item | Detail |
|---|---|
| What it compares | Two complete birth charts, measured against each other. |
| What it needs | Date, exact time and place of birth for both people. No account, no email. |
| What it returns | An overall score, six category scores, the five strongest aspects, house overlays and any critical contacts. |
| House system | Placidus and the tropical zodiac, for both charts. |
| What it is not | Not a verdict on a relationship and not a prediction; the numbers describe geometry. |
Frequently asked questions
What is a synastry chart?
A synastry chart sets two birth charts against each other and measures the aspect each planet in the first chart makes to each planet in the second. The result names those contacts, how close each one is to exact, and which houses of one chart the other chart's planets fall into.
What house system do you use?
Placidus, with the tropical zodiac, for both charts. The house overlays are read from those same Placidus cusps, so a different house system would move some of them.
Do I need my exact birth time?
Yes — for both people. The calculation engine requires an hour and a minute for each chart, because the Ascendant, the Midheaven and every house overlay depend on them. Without a birth time the comparison is not calculated rather than guessed.
Both charts use the Placidus house system and the tropical zodiac. The house overlays follow the same cusps, which is why the system is named here rather than left implicit.
Aspects come from calculated planetary positions, and every row carries its own orb — the distance in degrees from an exact angle. Tighter orbs rank higher in the list.
The scores summarize geometry, not people. Astrology is not a predictive science; it is read here as a symbolic language.
How Merolot calculates and who writes →