Synastry keeps both natal charts intact. It compares one person’s planets, angles, and houses with those of the other person.

The comparison can include aspects between the two sets of planets. It may also include house overlays when the birth times are reliable. These techniques are used to consider how one person’s chart contacts the other person’s chart.

For example, a synastry reading might examine an aspect between one person’s Mercury and the other person’s Moon. Within astrological interpretation, this may raise questions about how communication and emotional responses interact between the two people. The meaning depends on the type of aspect, its orb, and the other patterns in both charts.

Synastry is commonly used for questions about attraction, communication, emotional exchange, recurring disagreement, and the ways two people respond to one another.

A midpoint composite chart uses the positions in two natal charts to calculate a new set of points. The composite Sun is placed at the midpoint between the two natal Suns. The same method is applied to the Moon and the other planets.

The resulting chart is a mathematical construction. It does not describe a real arrangement of planets that existed at a particular time and place. In astrological practice, it is interpreted as a way of examining themes that appear when the relationship is considered as a whole.

A composite Mercury, for example, may be interpreted in relation to communication within the relationship. A composite Saturn may be considered in questions involving responsibility, pressure, duration, or boundaries. These interpretations still depend on the rest of the composite chart and the context of the relationship.

Synastry is generally better suited to questions about the interaction between the two people. It can help an astrologer examine why a particular exchange feels easy, why a disagreement keeps repeating, or why the two people respond differently to the same situation.

A composite chart is generally used for questions about shared relationship patterns. It may be considered when looking at how the couple functions together, which concerns become central over time, or how the relationship handles responsibility and change.

These are different interpretive perspectives. They should not be treated as competing compatibility scores.

Suppose communication is the main concern. Synastry can show the cross-chart contacts involving each person’s Mercury, Moon, or other relevant points. This may help describe how one person’s way of speaking meets the other person’s way of processing emotion.

The composite chart approaches the question differently. Its Mercury and related aspects are interpreted as part of the communication pattern associated with the relationship overall.

The two methods may emphasize different things without one of them being wrong. The purpose of using both is to understand whether the issue appears mainly in the interaction between the individuals, in the shared relationship pattern, or in both places.

Reliable birth times are important for chart angles, houses, and house overlays. If either person’s birth time is unknown, synastry houses involving that person cannot be used with the same confidence.

Many cross-chart planetary aspects may still be available. However, the Moon and other factors that move meaningfully during the possible time range need to be qualified.

Composite planetary midpoints may also remain available, depending on the underlying natal positions. Composite angles and houses should not be presented as reliable when the birth information does not support them. Horoscope Room omits or qualifies these time-sensitive details instead of filling them in with a guessed time.

Horoscope Room uses the chart methods supported by the birth information and relevant to the question being asked. Synastry can provide detail about the interaction between the two people. A composite chart can add another perspective on patterns associated with the relationship overall.

The chart calculations remain separate from the context you provide. Your relationship history helps determine which supported patterns need explanation in the final reading.

Read What Is Synastry? for a closer look at aspects, continue with What Is a Composite Chart?, or learn more on How Horoscope Room Works.