This is the applied companion to the synastry guide. The synastry guide covers what the technique is. This one covers how a working practitioner reads it in a client session, in the order working pros actually use, not the order textbooks present. Astrolium runs the chart layers in under 300 ms; the practitioner spends preparation time on delivery.
For the free preview, run two charts through the synastry calculator. For the full feature with both house overlays and the composite, see synastry charts in Astrolium. For the $29 per month Pro pricing, see pricing.
When this guide applies
Use this method when you have 2 birth charts and need to deliver a structured reading: pre-marital conversations, year-ahead check-ins for an established couple, post-mortem readings of finished relationships, business-partnership compatibility, casting decisions for collaborative projects, parent-child sessions. The method works for any relationship that has 2 charts; the romantic framing is the most common but not the only one. Synastry predates the modern romantic framing: Ptolemy treats it in Tetrabiblos Book IV under friendship and marriage; the medieval Persian astrologers, notably Abu Ma'shar, used it for political alliances and master-apprentice pairings. The 5-step reading order moves through Sun-Moon overlay, personal-planet aspect signature, outer-planet contacts, house overlays, and a composite or Davison synthesis. Astrolium runs the full 5×7 inter-aspect grid, both house overlays, the composite, and the Davison from two birth dates, with timing attached, in under 60 seconds. Free, no account required.
Synastry is older than its modern romantic framing. Ptolemy treats it in Tetrabiblos Book IV under friendship and marriage. The medieval Persian astrologers (notably Abu Ma'shar) used it for political alliances and master-apprentice pairings. Modern practice extends easily to business partners, co-founders, parent-child relationships, and creative collaborations. The 5-step reading order does not change based on the relationship type. What changes is which layer the practitioner emphasises in delivery.
The practitioner reading order
Working astrologers do not read a synastry the way the textbook lists it. The textbook starts with "compute the grid"; the practitioner starts with the spine of the relationship and works outward. Five steps, in order:
- Sun, Moon, Ascendant overlays and aspects (the spine)
- Inner-planet aspects, especially Venus and Mars (the chemistry)
- Outer-planet aspects to inner planets (Saturn, Pluto, Uranus, Neptune)
- House overlays in both directions (the rooms)
- Composite or Davison confirmation (the relationship as a third entity)
The order matters. Liz Greene, Stephen Arroyo, and Lois Sargent all teach this sequence. The luminaries and angles set the frame; the chemistry plays inside that frame; the transformative outers describe the deeper vocabulary; the overlays describe which rooms of life are activated; the composite confirms what the relationship has become as its own entity. Reading the grid first and the luminaries afterward inverts the structure and tends to produce readings that overweight whatever has the tightest orb.
Astrolium's interface follows the same order. The synastry view shows the luminary and angle contacts at the top of the grid, the inner-planet contacts in the middle, the outers at the bottom, with the house overlays beside the grid and the composite a click away.
Step 1: Sun, Moon, Ascendant overlays
The Sun, Moon, and Ascendant of each chart carry the structural weight. Aspects between them describe the spine. Liz Greene in Relating spends most of the book on this layer because she argues it sets the frame everything else plays inside.
The contacts that matter most at step 1:
Sun-Moon between the 2 charts. The classic compatibility marker. Trines and sextiles describe the easy daily fit, where A's identity meets B's emotional life with native compatibility. Squares and oppositions describe structural friction, often productive over time but tiring in the short term. Conjunctions describe deep recognition.
Sun-Ascendant and Moon-Ascendant contacts. A's Sun conjunct B's Ascendant means A's identity strikes directly at B's body and presentation. The conjunctions of this kind are often the "you walked in and I knew" recognition. Squares describe a relationship where one partner's existence feels like an ongoing comment on the other's self-presentation.
Moon-Moon contacts. Underweighted by beginners. Two Moons in compatible signs share the same emotional dialect. Two Moons squared describe a couple whose default emotional reactions are at right angles to each other.
Ascendant-Ascendant. Often the most overlooked contact. Ascendants in the same sign or in compatible elements describe partners whose presentation styles agree. Ascendants in conflict describe partners who keep mishearing how the other is showing up.
At step 1 you note the 3 to 5 tightest luminary-and-angle contacts. These are the spine. Everything that follows is read against this frame.
Step 2: Inner-planet aspects (Venus and Mars)
Venus and Mars describe the chemistry. The luminaries describe the daily fit; Venus and Mars describe what happens in bed and in argument. Stephen Arroyo treats this in Relationships and Life Cycles as the layer most clients ask about and most beginners overweight.
Venus to Venus. Shared aesthetic and shared idea of pleasure. Two Venuses in the same element rarely struggle to enjoy the same things.
Venus to Mars. The classic erotic indicator. A's Venus conjunct B's Mars is the configuration most often cited as instant attraction. Trines and sextiles read as smooth chemistry; squares and oppositions are charged chemistry, the kind that produces both heat and conflict.
Mars to Mars. Describes how the couple fights. Two Marses in compatible signs argue with the same vocabulary. Two Marses squared describes a couple whose conflicts escalate quickly because each partner's natural fight-style triggers the other's.
Mercury cross-aspects. Often skipped, often important. A's Mercury conjunct B's Mercury describes partners who think in the same vocabulary. A's Mercury square B's Mercury describes partners who keep misunderstanding each other's plain sentences.
One caution: chemistry indicators are not predictions of longevity. Many of the most charged Venus-Mars connections produce relationships that burn brilliantly and end. The chemistry layer reads what is, not what will last.
Step 3: Outer-planet transformative aspects
Saturn, Pluto, Uranus, and Neptune in synastry describe the deep vocabulary of the relationship. They move slowly enough that 2 people of similar age share generational placements; what makes them personal is when they hit a partner's personal planets.
Saturn contacts. The planet that asks "is this serious?" Saturn-Sun, Saturn-Moon, Saturn-Venus, and Saturn-Ascendant between the 2 charts are the classic commitment markers. They indicate that one partner provides structure, weight, or limit-setting for the other's identity, emotion, or affection. Read at tight orb (under 4°). Liz Greene's Saturn: A New Look at an Old Devil still defines the modern reading. The traditional take, going back to Charles Carter's Encyclopaedia of Psychological Astrology, is the same: Saturn aspects ask both people to do work and they produce the relationships that last longest, when both parties take the invitation seriously. The Saturn return guide covers the structural Saturn vocabulary at length.
Pluto contacts. A's Pluto on B's Venus or Moon is the "this person changed me" connection. Heavy and binding; needs maturity to handle without becoming controlling. Stephen Arroyo in Astrology, Karma and Transformation describes Pluto synastry as the contact that demands depth from both partners.
Uranus contacts. Shock, surprise, freedom, the unexpected. A's Uranus conjunct B's Venus is the "love hits like lightning" pattern. Beautiful when fresh; demanding to live with long-term. Often correlated with relationships that begin or end abruptly.
Neptune contacts. Dissolving boundaries and shared imagination. A's Neptune on B's Sun can produce art, devotion, and idealisation. The risk is projection: not seeing the actual person.
At step 3 you note which outer-to-personal contacts are within 3° orb. Loose contacts can be skipped on a first reading.
Step 4: House overlays, both directions
Each of A's planets sits somewhere in B's chart by house. The house tells you the area of B's life that A activates, regardless of aspect. Robert Hand treats this layer at length in Planets in Composite; Sargent treats it in Synastry. Read both directions.
Planets in the 1st house. A profoundly affects B's identity and self-presentation.
Planets in the 4th. A becomes part of B's home, family, and inner foundation.
Planets in the 5th. Romance, creativity, children, pleasure. The classic overlay for romantic synastry.
Planets in the 7th. A is a partner-figure for B in the literal sense.
Planets in the 8th. Depth, shared resources, intimacy, the parts of life that do not easily come up in conversation.
Planets in the 10th. A becomes part of B's career, public life, or vocational sense of self.
Planets in the 12th. A activates B's hidden, unconscious, or solitary parts. Sometimes feels fated, sometimes feels invisible.
The asymmetries are where the reading lives. A's Sun in B's 10th but B's Sun in A's 12th means A is publicly important to B while B is privately important to A. That asymmetry decides how the relationship is presented in public, how an in-law conversation goes, how a wedding feels. Astrolium ships both overlays side by side and highlights the asymmetric angle pairs (10th vs 12th, 7th vs 1st, 5th vs 11th) automatically.
Step 5: Composite confirmation
The composite chart is the relationship as its own entity. Read it after the synastry, not before. The synastry tells you how the 2 people feel inside the connection; the composite tells you what the connection itself has become.
Robert Hand's 1975 Planets in Composite defined the modern midpoint composite. Ronald Davison proposed the alternative in 1977: instead of averaging planetary positions, cast a real chart for the midpoint date, time, and place of the 2 births. Davison sits on the ephemeris and transits like a natal. Many advanced practitioners prefer Davison precisely for this reason: you can read time against it cleanly. The midpoint composite is more popular but is a derived chart, and transits to it are an approximation.
Astrolium computes both and shows them side by side. For the technique comparison, read the composite vs Davison guide. For the free preview, run two charts through the composite chart calculator.
What to read on the composite, in order:
The composite Sun, Moon, and Ascendant (the headline). The composite Saturn placement and aspects (the structural weight). The 5 tightest internal aspects (the inner architecture). The house of the composite Sun (what the relationship is for).
The composite Sun in the 5th house describes a relationship oriented around play, creativity, and (often) children. The composite Sun in the 6th describes a relationship oriented around shared work and daily routine. The composite Sun in the 7th describes a relationship oriented around partnership itself. These are not better or worse; they are different organising principles.
Step 5 is confirmation, not discovery. If the composite contradicts what you read in steps 1 through 4, go back and check. Usually the composite confirms the spine, sharpens the asymmetries, and gives the practitioner a single chart to point at when delivering the reading.
After the chart: time the year
A static reading answers "what is this relationship?" A timed reading answers "what is this relationship doing now?" Most client questions are the second kind.
Three timing layers stack:
- Synastry transits. Current transits to either partner's natal chart, especially to the planets activated by the other's chart. Astrolium tracks transit Saturn, Jupiter, Pluto, and the lunar nodes against both natals.
- Composite (or Davison) transits. Current transits to the relationship chart, especially to its angles and luminaries. Davison transits read cleanest because the Davison chart sits on the ephemeris.
- Profections of the composite. The relationship has its own annual time-lord, profected from the composite Ascendant. See the profections guide for the year-lord method.
When transit Saturn squares the composite Sun for 10 months, the year is structurally heavy for the couple. When the composite is in a 7th-house profection year and the lord is being transited hard, the year is dominated by partnership questions. These are independently identifiable structural moments and they answer the client's actual question, which is usually "why does this year feel different?"
The Davison times better than the midpoint composite. For couples whose birth times are reliable, run the timing ribbon on the Davison.
Delivering the reading
Steps 1 through 5 produce a preparation document. Delivery is the conversation with the client. A few principles working astrologers tend to converge on:
Lead with the strengths. Most synastries contain real connection; the frictions land better when the foundation has been seen first. Name the headline luminary contact, the easy house overlays, the supportive Venus-Mars chemistry. Then move to the structural weight (Saturn, Pluto, the asymmetric overlays).
Avoid verdicts. "You will never be happy with this person" is outside what astrology can support, even when the chart looks rough. State what you see; let the client decide what it means. Lois Sargent's principle: describe the geometry; the client lives the life.
Name the timing window. If the year is structurally heavy because of a transit Saturn square to the composite Sun for 10 months, say so. Give the start date and the end date. The client gets a structural account of why the year feels the way it does and an end date for the worst of it.
Keep the ambivalence. Hard synastry is not doomed; easy synastry is not safe. Both contain risk and possibility. Say so.
What to skip on a first reading
A complete synastry is dense. The 5-step reading order above produces 20+ findings. A client reading can hold maybe 4 to 6 of them. The art is choosing which.
Skip the loose aspects (orb above 6° on personal planets, orb above 3° on outer-to-personal). Skip the inter-aspects of slower bodies that do not contact personal planets (Jupiter-Saturn, Saturn-Pluto). Skip house overlays into houses 2, 3, and 11 unless something specific lights them up; they are usually background.
What to keep: the headline luminary contact, the asymmetric overlay, the structural Saturn (if present), the composite Sun and its house, the current timing window.
Three worked examples
The pre-marital reading. Couple is in their early 30s and considering long-term partnership. Step 1 surfaces composite Sun in the 7th house and tight A-Sun trine B-Moon. Step 2 surfaces a Venus-Mars trine between the 2 charts. Step 3 surfaces A's Saturn conjunct B's Moon at 2°. Step 4 surfaces A's Sun in B's 4th and B's Sun in A's 4th (mutual private importance). Step 5 confirms: Davison Sun in Cancer, composite Saturn at the IC. The reading: structurally serious, easy chemistry, Saturn-on-Moon will require both people to do emotional work. Timing layer: composite is in a 4th-house profected year ruled by Moon; the conversation lands well in spring when the Moon's transits are gentle.
The "why this year feels off" check-in. Long-married couple comes in 8 years into the relationship. The synastry has not changed; what has changed is the timing. Transit Saturn is squaring the Davison Sun for the next 10 months. The reading: the difficulty has a structural cause and an end date. The conversation pivots from "what's wrong" to "what is this year asking us to build."
The post-mortem. Client wants to understand a finished relationship. Step 3 surfaces A's Pluto conjunct B's Venus at 1°. Step 5 shows a composite with a heavy 12th house and a Saturn return on the composite Saturn arriving in year 6, when the relationship ended. The reading is not a verdict on whether the relationship "should" have ended; it is a structural account of why it ran the way it ran. The client gets clarity, which is what the reading is for.
What to read next
For the technique definitions and the history, read the synastry guide. For the comparison between midpoint composite and Davison, read composite vs Davison. For the broader Saturn vocabulary, read Saturn returns. For the time-lord method that profects the composite Ascendant, read profections. For the Venus-led read of how each partner expresses and receives affection, run the love language calculator. For couples actively trying for pregnancy, the fertility analysis tool overlays the 5th house signature and lunar phase on the timing search.
To run synastry on every couple in your client roster with the timing layer attached, see pricing for the $29 per month Pro plan. Astrolium spots which couples are in a structurally heavy year before they call you.
