What synastry compares
Synastry places two complete charts against each other and asks what touches what. It is not an average of two personalities and it is not a compatibility test in the psychometric sense; it is a description of the geometry between two sets of positions, read for what that geometry tends to feel like.
Three separate things come out of that comparison, and they answer different questions. The cross-aspects describe the pull between you. The house overlays describe which area of life it plays out in. The composite chart, built from midpoints, describes the relationship as an entity in its own right.
Cross-aspects, and why the orb decides everything
A cross-aspect is an angle between one person's planet and the other's. The full list in a typical comparison runs to well over a hundred contacts, which is why a raw list is close to useless without the orbs.
Orb is the distance from exactness. A contact within one degree is doing real work and both people will usually recognise it without being told. A contact at six degrees is present in the arithmetic and largely absent from the experience. The tables here are sorted by orb for that reason, and the tightest contacts are the ones to read first.
| Orb | How it tends to show |
|---|---|
| Under 1 degree | Unmistakable; often the first thing either person mentions |
| 1 to 3 degrees | Clearly present and recognisable once named |
| 3 to 6 degrees | Background colour rather than a feature |
| Over 6 degrees | Listed for completeness; do not build a reading on it |
Which contacts carry the most weight
Not all bodies count equally. Contacts involving the Sun, the Moon, Venus, Mars and the ascendant are the ones that consistently describe how a relationship feels from inside, and the calculator pulls those out separately before showing the full list.
Sun to Moon contacts are the most reported and the most durable. Venus to Mars describes attraction specifically, and describes it well enough that a strong Venus to Mars comparison with nothing else behind it is a recognisable pattern: intense, mutual and frequently short.
Saturn contacts are the ones people are warned about and the ones that hold a relationship together over decades. They feel restrictive early and load-bearing later, which is roughly what Saturn does everywhere else in a chart.
House overlays, which most tools skip
An overlay is where one person's planets fall in the other person's houses. It is asymmetric, and the asymmetry is the point: your Venus in their seventh house is a different experience from their Venus in your seventh.
The overlay decides the arena. The same Venus contact reads as domestic in the fourth house, professional in the tenth and private in the twelfth. Reading cross-aspects without overlays produces a list of feelings with nowhere to happen.
Both directions are shown separately here, because each person is living in a different one.
The score, and what it is worth
The number at the top weighs how exact each contact is, how heavily the bodies involved normally count, and whether the angle is an easy one. It is a summary of the list below it and nothing more.
It should not be read as a verdict. A score of sixty with three exact Venus contacts describes a livelier relationship than a score of eighty with none, and no configuration of two charts makes a relationship work or fail. What synastry describes reliably is texture: what comes easily, what needs saying out loud, and what will keep coming back.
The reason a score is offered at all is that people will construct one anyway, usually worse. Showing the arithmetic is better than leaving it implied.
Hard aspects are not bad news
Squares and oppositions between two charts are routinely reported as problems, and comparisons consisting entirely of trines and sextiles are routinely reported as dull. Both observations recur often enough to be worth taking seriously.
A square describes friction that produces motion. In a relationship that usually means the two people keep having the same argument, and that the argument is about something real. An opposition describes complementary opposites, which is the most common signature in long marriages and also in long feuds.
What genuinely predicts difficulty is not the aspect type but the absence of anything else. A comparison with one hard Saturn contact and a dozen supportive ones is not the same as a comparison with three hard Saturn contacts and nothing else.
Birth times, and what happens without them
Synastry works without birth times, at reduced resolution. Every planet-to-planet contact survives, because those depend only on the date. What disappears is anything involving the ascendant or the Midheaven, and both house overlays, since houses need an hour.
That is a real loss. The overlays are half of what makes synastry specific, and a comparison of two timeless charts is a description of chemistry with no setting. If only one of you knows their birth time, one direction of overlay is still available, and the calculator will show it.
The composite chart
The composite is built by taking the midpoint of each pair of placements: your Sun and their Sun produce a composite Sun somewhere between them. The result is not either person and not an average of their personalities; it is a third chart with its own logic, read as the relationship itself.
Couples frequently recognise a composite chart faster than they recognise their own synastry, because it describes the thing they are both inside rather than what each of them contributes. It is shown at the bottom of the reading, and there is a dedicated composite calculator if you want its houses and internal aspects in full.
Common questions
Does a high score mean the relationship will work?
No. The score summarises the contact list beneath it and nothing more. No configuration of two charts makes a relationship succeed or fail; what synastry describes is texture, not outcome.
Do we both need birth times?
Not strictly. Every planet-to-planet contact works from the dates alone. What you lose without times is the ascendant and Midheaven contacts and both house overlays, which is a real loss since the overlays describe where the relationship actually plays out.
Are squares and oppositions bad?
Not on their own. A square describes friction that produces motion, and oppositions are the commonest signature in long marriages. What predicts difficulty is a comparison with hard contacts and nothing supportive alongside them.
What is a house overlay?
Where one person's planets fall in the other person's houses. It decides the arena: the same Venus contact reads as domestic in the fourth house and professional in the tenth. It is asymmetric, so both directions are shown.
How is the composite chart different from synastry?
Synastry compares two charts. A composite takes the midpoint of each pair of placements and treats the result as a third chart describing the relationship itself, rather than either person in it.
Which contacts should I read first?
The tightest ones. Sort by orb and start with anything inside a degree, particularly if it involves the Sun, Moon, Venus, Mars or an ascendant. A contact at six degrees is listed for completeness and should not carry a reading.