Synastry, Composite & Davison Charts Explained

Synastry is the oldest and most direct of the three: you take two complete birth charts and lay one on top of the other like a biwheel, then measure the angular distance — the aspect — between every planet in chart A and every planet in chart B. A tight Venus-Mars conjunction between two people means something specific happened astronomically at the moment of their meeting's astrological backdrop, regardless of which sign either Sun falls in. Synastry never produces a new chart of its own — it's a comparison, not a construction.

Composite and Davison charts do the opposite. Both take two birth charts and combine them into one new chart that represents the relationship itself as an entity — but they get there through completely different math, which is why treating them as interchangeable is the single most common mistake in how people read about relationship astrology online.

In synastry, it's not just which planet contacts which — it's which of your partner's planets fall into which of your houses. A partner's Sun landing in your 1st house makes their presence feel immediate and identity-shaping. The same Sun landing in your 4th makes them feel like family before the relationship has earned that closeness. Six houses do most of the interpretive work.

The 7th house specifically — the house Western astrology assigns to marriage, contracts, and open partnership — is where astrologers look first. A partner's Venus falling there tends to read as ease and mutual regard; their Mars falling there tends to read as competitive, driven energy that can go either toward passion or toward friction, depending on the rest of the comparison.

A composite chart is built by taking the midpoint between each pair of matching planets — your Sun and their Sun produce a composite Sun, your Moon and their Moon produce a composite Moon, and so on through every planet and angle. The result is read exactly like a natal chart, except the 'person' being read is the relationship itself: its own Sun sign, its own Ascendant, its own house placements.

This is why composite charts are typically read only once a relationship already has some history — the technique assumes there's an entity to describe. A brand-new connection has synastry (how the two individuals interact) but arguably no composite identity yet worth interpreting on its own.

A Davison chart takes a different route to the same goal as a composite: instead of averaging planetary positions after the fact, it averages the two people's actual birth date, time, and location, then calculates a genuine chart for that resulting moment and place — as if the relationship itself had been born then. Because it corresponds to a real point in time, a Davison chart can be read with real transits, progressions, and returns applied to it, the way you would for an actual person's chart. A composite chart, being a mathematical construction with no real moment behind it, generally cannot.

In practice, most people don't need to choose only one. Synastry is where you start — it's the only technique of the three that tells you anything about the two individuals as they actually are. Composite and Davison charts both come after, when you want to understand the relationship as something with its own trajectory rather than just two people's overlapping charts.