The Foundation

Synastry is, to put it simply, the astrology of relationships. It’s commonly referred to as compatibility, though most references to astrological compatibility only reach the very surface of synastry, and thus are not reliable.

Much of astrological compatibility refers solely to the sun signs, or rejects the importance of sun signs entirely. Neither approach is correct. Think of the saying “can’t see the forest for the trees” – in this case, some can’t see the trees for the forest. There must be balance.

All of the energies in the natal chart must be acknowledged when studying synastry, not just the Sun’s or that of Venus or Mars, and not just ruling elements.

In the following article, I will explain the very basics of this complex aspect of synastry.

Synastry Basics (2)


Heavenly Bodies











The Sun

Synastry is often so simplified that many only acknowledge Sun signs when considering compatibility, which is far too superficial to actually provide much insight into a relationship.

In the personal chart, the Sun represents the foundation of the personality, it is vital in understanding the individual. But it takes a backseat to other planets when it comes to matters of friendship, love, communication, and the like. Still, the Sun sign shape many key aspects of the self, and thus it is still important in relationships.

An individual’s world view, their growth, their path in life are all guided by the Sun. The Sun sign is one’s purpose, and as such it can be difficult for people with incompatible Sun signs – and thus incompatible drives and views – to become close if the rest of their charts is not harmonious.

The Sun’s position in relation to the other planets, and its position in the houses, is also key to understanding compatibility.

The Moon

This is our emotions, our needs, and how we desire to be nurtured and to nurture in return. Moon signs are extremely important to understanding compatibility for these reasons.

A struggle many will face when growing emotionally is the realization that the way we need to be loved is not the way others need to be loved. This is the great lesson of the Moon in synastry, and what makes it so important in a relationship.

This heavenly body rules over the unseen within us: The unconscious, conditioning remaining from childhood, and so many parts of us we may not even know about ourselves are all controlled by the Moon. These subtle, hidden parts of us are often drawn out in relationships. We cannot truly become close to others without baring certain parts of ourselves. It can be ugly, difficult, and terrifying, but also deeply rewarding.

Compatible Moon signs are highly important in any relationship, romantic or platonic.

It is also the part of us that is truly receptive to others. How we empathize, express our care, and seek to comfort.


Communication is ruled by this planet, and as communication is key in any relationship, Mercury is key to synastry. Not only that, but Mercury rules decision making and other thought processes, which is highly important when building a relationship.

Unlike other heavenly bodies, focusing on the Element of this position is something you should focus on, and consider with care. Compatible, or harmonious, elements can make communication natural and easy. Incompatible elements, on the other hand, can create discord.


Often the main focus in synastry, Venus is a clear player in compatibility as the planet of love. This is the core of all romantic relationships and attraction.

Venus determines how we love, what we look for in a lover, and what we expect of a union. It also strongly influences attitudes surrounding possessions and money, which can raise issues in any long-term relationship. In addition, Venus determines many of our values, at least social ones, and thus it is another influencer of our ideals and goals.

In ways, it acts similarly to the Moon, ruling over our emotions. But, Venus specializes in the emotions that are and must be expressed between lovers.


This is the body of physicality. Mars rules our physical attraction, desires, and compatibility. Not only this, it is instinct. The counterpart of Venus, this is the need and drive to our care and compassion. Venus is the emotional and mental, Mars the innate and the physical.

Mars is not a hinge position – if a couple’s Mars signs are not compatible it will not ruin the relationship. But, it can certainly help or hinder, especially if it is a dominant body in either individual’s chart.

Interaspects, aspects created between two charts rather than within one, that involve Mars can create issues with the physical relationship between two people, or create general conflict.

The key thing to remember is that the conflict Mars creates is not necessarily negative. It can actually greatly help a couple, giving them something to bond over, letting them air out their grievances, or simply something to grow from.


Jupiter’s main influence in synastry is through aspecting bodies such as Venus, which is true of most outer heavenly bodies. Through such aspects, this planet bestows luck and good fortune as long as the aspect is a positive one. Even challenging aspects, however, can assist greatly in the growth of a relationship.


Again, Saturn is like Jupiter, its influence on compatibility is through interaspects. Saturn bestows stability through these aspects, granting a couple a strong foundation for their relationship.

At the same time, one must remember that Saturn is not only the planet of commitment but restriction. While interaspects between Saturn and the inner bodies can create solid, long-term relationships, there can be a struggle to reach that point.


Uranus interaspects creates unusual relationships, fascination, and general instability between individuals. There is a freedom and playfulness granted by this aspect, but it can sometimes go too far. Without the stability of Saturn or other influences in other parts of the chart, this can be a difficult influence in synastry.


Neptune interaspects are somewhat similar to aspects of Uranus: The couple will experience a strange attraction, a fascination with each other. This can create a relationship that is more idealized than real. Again, Neptune’s influences are delicate and difficult to manage.


Interaspects involving Pluto create intense emotional attachments, a primal draw not unlike the influences of Mars, and general instability. The passion granted by these aspects is unmatched, but it can be too much, creating jealousy and unhealthy emotions.



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