Understanding synastry: what comparing two charts really shows

Sun sign compatibility is the most popular and the least accurate way to compare two people astrologically. Two sun signs say almost nothing about how two charts relate, because a birth chart is made of ten bodies, not one. This is exactly where synastry begins.

What synastry measures

Synastry overlays two complete birth charts and measures the angles between one person’s planets and the other’s. If your Venus sits at the same degree as the other person’s Mars, that is a contact. If your Saturn squares their Sun, that is another. The meaning comes from the pattern of these contacts as a whole.

A few examples of what the contacts carry:

• Sun and Moon between two charts stand for the basic sense of familiarity, the question of whether you feel seen.
• Venus and Mars stand for attraction and the style in which closeness and friction get expressed.
• Saturn contacts stand for structure and commitment, and, depending on the angle, for pressure too.

No single contact decides anything. A Saturn square is not a verdict, it is a place where commitment and constriction sit close together. What comes of it is not written in the chart.

Composite is something else

Alongside synastry there is the composite. It computes a third, separate chart from the midpoints of both charts: not you, not the other person, but the relationship as its own entity. Synastry shows how two people act on each other. Composite shows what arises between them as a third thing. Both answer different questions, and both need real angles, not rules of thumb.

Why a comparison needs calculation, not clichés

Synastry is computation heavy: ten bodies against ten bodies, plus the Ascendant and Midheaven, each angle with its own orb. That is exactly why the gap between a serious calculation and a sun sign table is so large. Astraleria computes the comparison with real aspect angles and staggered orbs, and the first comparison is free and stores nothing: you type in the second person, you see the actual contacts, and the data never leaves the device.

Astraleria deliberately shows no percentage score. A number like 84 percent compatibility sounds precise, but it is invented, because there is no formula that pours human closeness into a percentage. Instead Astraleria names the archetype of the connection and lays out the contacts that support it. You see what the statement rests on, and you keep the judgment yourself.

If you want to see the contacts between two charts right now, without the app and without an account: the free synastry calculator computes them directly in your browser, using the same orbs as the app.