Birth chart guidesCompatibility
Synastry: how astrological compatibility works
By the Hourwyn team
Synastry is the comparison of two birth charts. Instead of matching sun signs, it measures the angles between one person's planets and the other's. Astrologers read those cross-chart aspects as the places where two people connect easily and the places where they rub. It needs both birth dates and birthplaces, and both birth times for a full comparison.
Why sun sign matching falls short
Sun sign compatibility compares one planet out of ten, which sorts every couple into one of 144 pairings. Synastry compares all ten planets in one chart with all ten in the other. Two people whose sun signs are said to clash can have many easy contacts elsewhere, and the reverse.
What gets compared
| Pair | What astrologers read from it |
|---|---|
| Moon and Moon | Emotional rhythm: how each person settles and what each needs |
| Sun and Moon | Whether one person's nature suits the other's needs |
| Mercury and Mercury | How the two talk, decide and disagree |
| Venus and Mars | Attraction and affection |
| Saturn to the other's personal planets | Commitment and pressure |
The angles are the same five aspects used inside a single chart. If one person's Moon is at 12° of Cancer and the other's Venus is at 14° of Pisces, the two are 118° apart: a trine with a 2° orb.
Synastry vs composite chart
| Synastry | Composite chart | |
|---|---|---|
| What it is | Two charts laid side by side | One new chart made from the midpoints of the two |
| What it describes | How each person affects the other | The relationship as a thing of its own |
| Where to start | Usually read first | Usually read second |
What synastry cannot tell you
No comparison of charts can say whether a relationship will last, or whether two people should be together. There is no evidence that it can, and a percentage score has no agreed formula behind it. Read a comparison as a list of themes worth talking about. Decisions about a relationship belong to the two people in it.
What you need
- Both birth dates and birthplaces.
- Both birth times, if known. Without them the rising signs and houses are left out and contacts to the Moon are approximate.
- The other person's permission. Birth details are personal data.
Common questions
Are synastry charts accurate?
The calculation is exact: the angles between two charts can be measured to a fraction of a degree. Whether those angles say anything about a relationship has not been shown in controlled research, so we present it as entertainment and a prompt for conversation.
Do I need my partner's birth time?
No, but the comparison is fuller with it. Without a time the rising sign and the houses are left out for that person.
Which should I read first, synastry or the composite chart?
Most astrologers start with synastry, because it keeps the two people separate, and turn to the composite afterward.
Is synastry only for couples?
The method works for any two people: friends, relatives or colleagues. Our report is written with a couple in mind.
Compare two charts
The Compatibility Report reads two charts side by side in six chapters, with every cross-chart aspect listed. $12, paid once.
Keep reading
Sources
- Synastry. Wikipedia.
The guides are written by Hourwyn with the help of AI tools. Astronomical and historical facts are checked against the sources listed under each guide. Astrology is described as a tradition and offered for entertainment. Nothing here is medical, financial, legal or psychological advice.