If you have ever read that two sun signs are compatible, you have read something that ignores almost everything about both people. Sun sign compatibility uses one placement out of dozens and treats everyone born in the same four-week stretch as interchangeable. Synastry is what astrologers actually use when they want to say something about two specific people.
Two charts, not two signs
A natal chart is a map of where everything was in the sky at the moment and place you were born. Not just the Sun — the Moon, Mercury, Venus, Mars, Jupiter, Saturn, and the angles that depend on the exact minute and city.
Synastry is the comparison of two of those maps. You take both charts and measure the angles between the planets in one and the planets in the other. Those angles are called aspects, and they are the entire substance of the reading. Where two planets sit at a close angle, there is a real connection between those two parts of the two people. Where they sit at a hard angle, there is friction.
This is why synastry says something and sun sign compatibility does not. Two Capricorns can have charts that grind against each other everywhere that matters. A Capricorn and an Aries can have four strong connections and one hard one. The signs are the headline; the aspects are the story.
What actually gets compared
Different astrologers weight things differently. Here is what we read, and why each one earns its place:
Sun — shared purpose. Whether you are pointed at the same thing in life, or politely walking in different directions.
Moon — trust and emotional ease. This is the one most people underestimate. Two people can be wildly attracted to each other and still find that living together is exhausting, and the Moon is usually where that shows up.
Venus — love and romance. How each person gives affection, and whether the way one gives it is the way the other recognizes it.
Mercury — communication. Whether an argument gets resolved or just repeated.
Mars — passion, drive, and how conflict gets handled. Mars is where chemistry lives and also where fights start.
Jupiter — growth and support. Whether being together makes each person bigger.
What happens when a birth time is missing
This is the part most compatibility tools quietly get wrong.
The Moon moves about thirteen degrees a day. Over the course of a single day it can change signs. So if you do not know what time someone was born, their Moon cannot be placed with certainty — and the Rising sign and Midheaven cannot be calculated at all, because both depend on the exact minute and the exact location.
Most tools handle this by defaulting the missing time to noon and printing a Moon, a Rising sign and a Midheaven as if they were real. You are never told. The reading looks complete and part of it is invented.
We do it differently. If a birth time is unknown, we leave out what cannot be verified, say so plainly on the portrait, and recalculate the weighting across the placements we can stand behind. A reading with five verified placements is worth more than one with six where the sixth is a guess. It does not help you and it does not hurt you — it is simply honest about what is known.
The layout adjusts too. Normally Mercury and Venus share a single combined summary box. When a birth time is unknown and the Moon comes off the scorecard, Mercury and Venus separate and each gets a box of its own. Nothing is left blank and nothing is padded — the portrait reorganizes around what can actually be verified.
Why we do not lead with a number
Compatibility scoring produces a number. We calculate one, and we can show it to you. But we do not put it at the top of the portrait, and the reason is worth explaining.
People read numbers as grades. Thirteen years of school teaches everyone that anything under seventy is failing. But compatibility scoring does not use a school scale — the range that real couples land in is not the range you were trained to read. A perfectly strong pairing can produce a number that looks like a bad report card, and the number tells you nothing you could act on.
So the portrait gives you a plain verdict for each of the six placements instead. Words, not grades. What is strong, what grinds, and what the two charts add up to.
The writing changes with the scores
Here is the part that most people do not expect. Hiding the number does not mean softening what it found.
The written sections are not a fixed template with the placements swapped in. Their tone is driven by the scores themselves. A pairing that scores well gets a warm read, because that is what the charts support. A pairing with real friction gets a blunter one — the language tightens, the difficulties get named, and nothing gets smoothed over to make the portrait more pleasant to hang on a wall.
So two couples never receive the same portrait with different names on it. The scoring decides what gets said and how directly it gets said, which means the writing carries the same information the raw number would have, in a form you can actually use.
You can check our work
Everything on a synastry portrait comes from astronomy. Where the planets were at a given date, time and place is not a matter of opinion — it is ephemeris data, the same tables astronomers use, and anyone can look it up.
Run both birth details through any free chart calculator and compare the placements to ours. They will match, by sign and by degree. That is the point. We are not asking you to trust an interpretation you cannot verify; the underlying positions are checkable, and the written sections are built on top of those positions rather than on flattery.
Plenty of compatibility content is written to make you feel good. That is easy to write and worth nothing. If two charts have a hard Mars aspect, we say so, because that is the part you would actually want to know.
Getting your own
Our Couples Compatibility Portrait puts both birth chart wheels side by side with the scorecard between them, five written compatibility sections, and The Verdict — what the two charts add up to as a pair. Every placement for both people is printed by sign and degree, so the whole thing is checkable.
It comes printed and framed and ready to hang, or as a print-ready file you take to a print shop yourself. Either person can have an unknown birth time and the portrait is still built correctly.
And if you want the real breakdown — the raw scorecard behind the verdicts, showing exactly where you shine and where you grind — that is the Couples Score Report, a ten dollar add-on delivered by email. Same six placements, with the numbers and the reasoning that produced them.
Or try it free first. Our chemistry check reads both charts against each other and tells you what's actually there — no account, nothing emailed to you.