Synastry explained: what every planet and aspect means in a relationship

Synastry is the technique of laying two birth charts over each other and reading the aspects between them. In a single chart the planets describe the different voices inside one person; in synastry one person's planet touches another's, and the chemistry of the relationship comes out of exactly those contacts. 'Why is talking to this person so easy?' and 'Why do we keep having the same argument?' usually have their answer in two or three prominent aspects. This guide walks through it planet by planet and aspect by aspect, so you can look at your own synastry and tell what flows from what is a lesson.

Synastry, composite and Davison: what's the difference?

All three belong to relationship astrology, but they answer different questions. Synastry asks 'what do we do to each other?' - two separate charts and the aspects between them. The composite builds a third chart from the midpoints of both charts and answers 'what is the relationship itself like?'. The Davison averages the two birth dates, times and places into a real chart in time and space, which means it can receive transits. In practice you read synastry first, then confirm the shared story with the composite or Davison.

Synastry shows the chemistry, the composite shows the relationship's character, the Davison shows how it moves through time.

What each planet carries in synastry

Every planet has a different job in a relationship. Personal planets (Sun, Moon, Mercury, Venus, Mars) drive the daily chemistry; social planets (Jupiter, Saturn) handle growth and durability; outer planets (Uranus, Neptune, Pluto) bring transformation and shadow. Here is what comes online when one planet touches another.

• Sun: identity and being seen. A planet touching the other's Sun either affirms or challenges their core.
• Moon: emotional safety, the feeling of home, the language of care. Long relationships usually hinge on Moon contacts.
• Mercury: pace of conversation, humour, being understood. Without Mercury contact you get 'I love you but we don't talk'.
• Venus: attraction, pleasure, tenderness, how you value someone. Romance largely lives here.
• Mars: desire, sexuality, tempo and conflict style. No Mars contact can mean polite but flat.
• Jupiter: generosity, optimism, growing together; it gives the bond room and faith.
• Saturn: responsibility, duration, boundaries. Binding - weight in hard aspect, endurance in soft.
• Uranus: electricity, sudden attraction, need for freedom; exciting but unstable.
• Neptune: idealisation, compassion, inspiration; boundaries can blur.
• Pluto: intensity, transformation, power dynamics; the deepest mark and the most work.
• Lunar Nodes: that fated feeling of meeting, the direction you travel together.
• Chiron: mutual healing and the triggering of an old wound.

What the aspects mean: conjunction, trine, sextile, square, opposition

An aspect is the angular distance between two planets and it sets the tone. The same pair tells a completely different story depending on the angle: a Venus-Mars trine is easy attraction, a Venus-Mars square is friction-charged attraction.

• Conjunction (0 degrees): the two energies merge and amplify each other. Sweetest or hardest, depending on the planets.
• Sextile (60 degrees): opportunity and easy cooperation; it needs a little willingness to activate.
• Square (90 degrees): friction, tension, action. It doesn't end relationships, it produces movement - and a repeating argument.
• Trine (120 degrees): natural flow, ease, acceptance. Too much of it can drift into comfort without spark.
• Opposition (180 degrees): polarity and complementarity; the 'you have what I lack' dynamic, extremely productive once balanced.
• Quincunx (150 degrees): different languages; an invisible tension that needs constant small adjustment.

A healthy synastry has both soft and hard aspects. All trines and sextiles is comfortable but static; all squares and oppositions is passionate but exhausting. The ratio is what matters.

The most talked-about pairs and what they really mean

• Sun-Moon: the classic long-term indicator. One brings identity, the other feeling; it feels like building a home.
• Moon-Moon: a similar emotional rhythm. Conjunction feels understood, square means different needs at the same moment.
• Venus-Mars: the clearest romantic and sexual axis. Flow in soft aspect, charged tension in hard.
• Venus-Venus: matching taste and love language; the pleasure of ordinary days.
• Mercury-Mercury: the quality of conversation; squares increase misreadings.
• Mars-Mars: tempo and conflict style; hard aspects argue over who leads.
• Saturn-Moon: one offers security, the other can feel tested. Very solid in mature hands, chilling in immature ones.
• Saturn-Venus: loyalty and continuity; in hard aspect love can feel conditional.
• Jupiter-Sun or Venus: the contact that opens luck and lifts morale.
• Uranus-Venus: sudden, intense attraction; fast start, continuity takes separate effort.
• Neptune-Venus: dreamlike and compassionate; watch for idealisation and disappointment.
• Pluto-Venus or Mars: magnetic, potentially obsessive intensity; without an honest talk about power it turns into control.

House overlays: which of their houses does your planet land in?

The most skipped and most revealing layer of synastry. Whichever house of your partner's chart your planet falls into, you animate that area of their life. The same Venus creates flirtation and fun in the 5th, partnership and marriage in the 7th, and secrecy or surrender in the 12th.

• 1st house: physical attraction, the feeling of being seen.
• 4th house: family and home feeling, a pull toward living together.
• 5th house: dating, play, creativity, children.
• 7th house: seriousness, partnership, long-term commitment.
• 8th house: deep bonding, sexuality, shared resources, transformation.
• 10th house: status, public visibility, career support.
• 11th house: friendship, shared goals, social circle.
• 12th house: a hidden, karmic or blurry bond.

Orbs: when does an aspect actually count?

The orb is how far an aspect is from exact. Synastry orbs are slightly tighter than natal ones, because a weak aspect simply isn't felt day to day. A practical scale: up to 8 degrees for the Sun and Moon, 6 for personal planets, 3-4 for outer planets. Under 1 degree, that aspect becomes the relationship's main theme and shows up almost daily.

Three tight aspects say more about a couple than ten wide ones.

A step-by-step reading order

• 1. Read both charts separately first; you can't interpret contacts without knowing what each person needs.
• 2. Look at Moon and Venus contacts: daily peace and tenderness live there.
• 3. Check Sun-Moon and Sun-Ascendant contacts: the sense of 'us'.
• 4. Look at Mars and the Venus-Mars axis: attraction and conflict tempo.
• 5. Examine Saturn contacts: will this hold up over time?
• 6. Leave outer planets for last; they add intensity but don't build a relationship alone.
• 7. Finish with house overlays: which area of life is this bond actually lived in?

The most common synastry mistakes

• Seeing one hard aspect and declaring it doomed; no single aspect is destiny.
• Interpreting house overlays without a birth time; with no time, trust aspects only.
• Comparing Sun signs only; the real information sits in the Moon, Venus and Mars.
• Mistaking Pluto or Uranus intensity for love; intensity and peace are not the same thing.
• Ignoring mutuality; one-directional contacts create an unbalanced dynamic.

Casting your own synastry

Add your partner or a friend in the My People section to see the compatibility score, element and modality balance and the full aspect list; the detailed synastry report adds house overlays, relationship dynamics and area-by-area interpretation. If you haven't cast your own chart yet, start with the natal chart tool in the Charts section, then move to the comparison.

One last note: synastry is not a compatibility exam, it's a user manual. A hard aspect doesn't say the relationship should end, it says you need to be conscious in that area. Two people can live very different relationships with the same chart pair; awareness is what makes the difference.