Most compatibility readings begin with each person's Sun sign. It is the easiest data to collect and the least useful. Two people can share a Sun sign and spend years failing to understand each other, and two signs that tradition calls incompatible can hold a household together for decades. The problem is rarely the data. It is the order the data is read in.
Why the order changes the reading
The Sun takes a year to travel the wheel and stays roughly thirty days in each sign. That means it describes enormous groups of people born in the same month: a layer of identity, not of living together. When a reading stops there, it ends up discussing archetypes instead of the relationship in front of you.
Daily life sits somewhere else. The Moon governs rhythm, rest, reaction under stress and the way someone asks to be loved. The Ascendant describes how a person walks into a room and what they expect from you before you speak. Saturn says who carries the weight and for how long. Compare Sun signs first and you are reviewing the cover of a book you have not opened.
There is a second effect worth naming: order also decides what gets discarded. A couple with a Moon square and a Sun trine will have more everyday friction than a couple with a Sun square and a Moon trine, even though the first combination sounds worse on any compatibility list. The first pair shares the morning sky. The second shares Sunday afternoon.
The order two charts are read in
This is the order I use, and the reason for each position.
1. Moon to Moon
This is the first real contact between two people who will sleep under the same roof. Two Moons in the same element understand each other without explanation: they know when the other needs quiet. Two Moons in square, on the other hand, ask for different things in order to calm down, and neither is wrong. When this layer fails, everything above it becomes effort. When it works, it holds far larger differences in place.
2. Moon to Saturn
This marks who holds and who feels held, and whether that exchange lands as care or as control. A Moon-Saturn contact usually points to a relationship that matures slowly but does not collapse at the first winter. It also marks the place where someone feels evaluated without having asked permission. Best named out loud than hidden.
3. Venus and Mars
Desire comes third, not first. Strong attraction convinces two people to move in together and tells them nothing about how they will argue over money or family. Venus shows what gets recognised as affection; Mars shows how someone pursues what they want. Read together they explain the opening impulse. Read alone, they explain why many intense relationships last less than they promised.
4. Saturn to the personal planets
This is where durability is read, not doom. Saturn does not destroy: it sets deadlines. In contact with the other person's Sun, Moon, Venus or Mars, the relationship asks for structure, patience and concrete decisions. Plenty of people read that weight as a bad sign and walk away from the very aspect that would have given them something that lasts.
5. House overlays
This layer answers a different question: what role do I play in the other person's life. One person's planets falling in the other's seventh house speak of partnership and mirroring; in the fourth, of home; in the tenth, of shared projects and reputation. This is where the reading stops being generic, and also where you need the exact birth time: without an Ascendant there are no reliable houses and none should be invented.
6. Nodes and Chiron
Last, because they describe direction, not a verdict. The nodes point to where each person grows and what kind of bond pushes that growth. Chiron points to the wound the other person brushes against without meaning to. That is material for a long conversation, not for a soulmate label.
A worked example with computed charts
So the order does not stay theoretical, here is an exercise with two sample charts. These are not real people: two birth dates with time and place, computed with Swiss Ephemeris in the tropical zodiac and Placidus houses, in Guadalajara.
| Point | Chart A | Chart B |
|---|---|---|
| Sun | 23°34′ Taurus | 10°21′ Scorpio |
| Moon | 16°36′ Capricorn | 16°31′ Gemini |
| Venus | 11°50′ Aries | 22°06′ Libra |
| Mars | 17°41′ Pisces | 25°23′ Scorpio |
| Saturn | 25°16′ Capricorn | 23°40′ Aquarius |
| Ascendant | 6°52′ Cancer | 26°27′ Capricorn |
With those positions, the contacts between the two charts that fall inside a reasonable orb are these:
| Contact | Aspect | Orb | How it feels |
|---|---|---|---|
| Saturn A to Ascendant B | Conjunction | 1°11′ | B feels taken seriously by A, sometimes too seriously. |
| Sun A to Saturn B | Square | 0°10′ | Heavy commitment: hard to let go, hard to rest. |
| Mars A to Moon B | Square | 1°11′ | Friction in daily rhythm: one speeds up as the other withdraws. |
| Jupiter A to Sun B | Trine | 0°58′ | Generosity and good humour; the aspect that makes it worth it. |
| Sun A to Mars B | Opposition | 1°50′ | Each pushes the other way when things get urgent. |
| Moon A to Venus B | Square | 5°30′ | Two different ways of showing affection, neither wrong. |
Read in order, the diagnosis is concrete and not at all romantic: a very strong foundation of commitment held by Saturn, real friction in the everyday rhythm, and an equally real relief from Jupiter. Had the reading started with each Sun, Taurus against Scorpio, the summary would have been a sign opposition and nothing more. It would have missed exactly what makes this combination work and what wears it down.
Look at the orbs too. A 0°10′ square does not behave like a 5°30′ one. The orb measures how close the contact is to exact, and exact contacts are the ones felt every day. Comparing synastries without reading orbs is like comparing two recipes by their ingredient lists and ignoring the quantities.
What synastry cannot tell you
Worth being explicit, because almost nobody is.
- It does not say yes or no. No combination of aspects obliges anyone to stay or justifies leaving. It describes tendencies and asks for decisions.
- It does not predict infidelity, money or illness. That is not in the chart, and whoever promises it is selling something else.
- It does not replace the conversation. A difficult aspect discussed openly weighs less than an easy one nobody names.
- It does not work the same without a birth time. Without a time there is no Ascendant and no houses: you can read an approximate Moon and the planetary aspects, and you should say so. If you do not have the time, see what can still be read in a chart without a birth time.
What data you need
Three facts per person: birth date, birth time and birth city. The city matters because it defines coordinates and time zone, and a badly converted time moves the Ascendant several degrees. The time matters more still: the Ascendant advances roughly one degree every four minutes, so half an hour can change the house where everything else lands.
If the birth certificate has no time, rectification techniques exist, but they are an estimate and should be presented as one. Better to say "I don't know" than to invent an Ascendant that sounds convincing.
If you want the full picture of a single chart before comparing, start with how to read a natal chart. The numerology side of compatibility, which needs no time or coordinates, is in numerology compatibility. The broader sign-by-sign comparison is in zodiac compatibility basics.
Common questions
What matters more in synastry, the Moon or Venus?
The Moon, for living together. Venus describes what is recognised as affection and what attracts; the Moon describes how someone rests, reacts to stress and needs to feel at home. If the goal is an everyday relationship, the Moon weighs more.
How wide an orb is valid between two charts?
It depends on the aspect and the planet. For contacts between luminaries, wide orbs of up to 8 degrees are accepted. For slow planets touching personal points, stay within 3 or 4 degrees. A 6-degree contact is felt, but it does not organise your life the way a 1-degree contact does.
Does synastry work for work or family relationships?
Yes, and in those cases house overlays are usually more useful than Venus and Mars. In a business partnership, what matters is which planets fall in the other's second, sixth and tenth houses; desire does not explain a company.
Can synastry be done with a chart that has no birth time?
A partial reading is possible: aspects between planets and the Moon's position with a margin of error. Houses and the Ascendant cannot be read. Any reading that claims otherwise is filling gaps.
If you want this reading done with your data and the other person's, see the compatibility reading: both charts are computed in full, overlaid, and delivered as a PDF with the reading order and exact orbs, not a list of labels.