AI Compatibility Reading

Why Sun-Sign Compatibility Is Only a Sliver of a Relationship

“Leo and Aquarius? Opposites, that'll be a fight.” Most compatibility talk starts and ends with two Sun signs. That is one planet out of ten for each person, and it says nothing about the Moon, which describes what each of you needs to feel safe, or the Ascendant, which colors the first impression and the everyday manner you meet each other with.

Two people with the same pair of Sun signs can have very different charts. One Leo may have a Moon in Cancer that wants quiet evenings at home; another may have a Moon in Sagittarius that gets restless after three days in one city. Their partners would feel the difference long before they felt the Sun sign.

Sign-pair pages are still a friendly place to start, and Cosine Astro has one for every Sun-sign pair, written without scores. But if you want to look at an actual couple, you need both charts and their exact positions. That comparison is called synastry.

What a Synastry Chart Compares: Cross-Aspects and House Overlays

Synastry takes each person's planets and measures them against the other person's. When your Moon sits at a meaningful angle to their Venus, that is a cross-aspect: a link from one chart to the other. Conjunctions, sextiles, squares, trines and oppositions are the major ones; the site also lists minor aspects. Each comes with an orb, the number of degrees it is off exact. The smaller the orb, the more noticeable the contact tends to be.

House overlays are the second layer. Your planets fall somewhere in the other person's houses, and theirs fall in yours. If someone's Venus lands in your 4th house, astrologers read it as warmth that shows up around home and family life for you. Overlays depend on birth times, because houses come from the Ascendant.

Cosine Astro calculates all of this with an astronomical ephemeris before any AI is involved. The cross-aspect list and the overlays are shown on the synastry page for free, so you can read the raw material yourself.

The Free Synastry Score Out of 30, in Plain Words

The synastry page also shows a score out of 30. It follows the method of the Italian astrologer Ciro Discepolo, and it is the only score anywhere on the site. It works like a checklist, not a judgment. It looks at a handful of fixed contacts between the two charts, mainly between the Suns, Moons and Ascendants, and adds points for each one it finds.

Any aspect between one person's Sun, Moon or Ascendant and the other's Sun, Moon or Ascendant earns 4 points. Two contacts earn more: Suns square or opposite each other earn 8 points, and one person's Sun conjunct the other's Moon earns 8, rising to 11 when the orb is within 2 degrees. The method also gives 4 points for an aspect between one person's Venus and the other's Mars, and 5 points when both Sun signs share a modality (both cardinal, both fixed or both mutable), unless the Suns already scored a square or opposition.

Discepolo's article gives the point values but not the orbs or a maximum. The orbs used for scoring, the rule that each pair of points counts once, the cap at 30 and the handling of unknown birth times are Cosine Astro's own choices. The result is graded from D (few links) to A+ (exceptional links).

Just as important is what the score leaves out. It does not look at Mercury, Jupiter, Saturn or the outer planets, at houses or the 7th house, at the soft or difficult tone of an aspect, or at anything about the people themselves. A high score means the charts are strongly tied together at the points this method weighs. It does not mean the relationship will be easy, and a low score does not mean two people are wrong for each other.

What the AI Synastry Analysis Adds When Both Charts Are Saved

The score and aspect list are free to anyone. When you sign in (with an emailed code, also free) and both charts are saved to your account, you can ask for an AI analysis of the pair. The AI does not calculate anything. It receives the computed contacts as structured text and interprets them.

The analysis looks at four themes from each person's side: attraction, harmony, shared hopes and passion. “From each side” matters. A contact can feel exciting to one person and unsettling to the other, and the reading says so instead of blending the two into one number. It then lists the main relationship themes the charts point to, such as how you each handle closeness, conflict or plans for the future.

After that you can keep asking questions about the pair, within a daily limit. Each answer is marked as AI-generated, ends with a References line naming the placements it used, and offers two follow-up questions, so you can check the reasoning against the chart.

Worked Example: Fictional Sample Charts A and B Score 24 out of 30

Here are two fictional sample charts. Person A was born on 14 August 1996 at 6:20 in Portland, Oregon: Sun in Leo, Moon in Leo, Leo rising. Person B was born on 3 February 1994 at 21:45 in Chicago: Sun in Aquarius, Moon in Scorpio, Libra rising. The site's code gives them 24 out of 30, grade A, which it labels “very strong links”.

Five contacts make up the score. A's Sun is opposite B's Sun, about 6.9 degrees from exact, for 8 points. A's Sun is square B's Moon, about 3.7 degrees, for 4 points. The two Moons are square, only about 1.0 degree apart from exact, for 4 points. A's Ascendant is opposite B's Sun, about 7.7 degrees, for 4 points. A's Ascendant is square B's Moon, about 2.9 degrees, for 4 points. That adds up to 24.

Notice what is missing. Both Suns are in fixed signs, but the 5-point bonus for that is not added, because the Suns already scored their opposition. B's Libra Ascendant makes no scoring contact with A's Sun, Moon or Ascendant, and there is no Venus–Mars aspect within the scoring orbs.

Every one of the five contacts is a square or an opposition. A tool that only looked for trines would call this pair a poor match. This method calls it very strongly linked. Both views see the same geometry; they just ask different questions about it.

Why Oppositions and Squares Between the Lights Count as Strong Contact

In traditional astrology the Sun and Moon are called the lights. A square or opposition between them used to be read as a warning. Discepolo wrote that he once held that view, then noticed many long marriages and partnerships with Suns square or opposite, and changed his mind. His scoring treats these contacts as signs of a significant bond, so the Sun–Sun square and opposition carry the most points of any single contact.

The idea is simple. A square or opposition is a strong angle. It keeps two people noticing, testing and adjusting to each other. That can feel like friction, but it is also engagement: neither person fades into the background. A trine may feel smoother and still leave less of a mark.

It helps to be careful about how strong the evidence is. Discepolo's own study of couples appeared in a journal he founded, and he described the result as close to, but not reaching, statistical significance. So the method is best taken as one astrologer's way of counting ties, not as proof of anything. Cosine Astro's grade labels say this plainly: grade A means more interplay, not necessarily more ease.

In the sample pair, the Moon square Moon within 1 degree is the tightest scoring link. A Leo Moon tends to want warmth shown openly; a Scorpio Moon tends to want depth and privacy first. A useful reading turns that into a question: what does each of us need when we feel hurt, and how would the other know?

Reading Difficult Synastry Aspects Without Fatalism

A square between your Moon and your partner's Mars does not mean you will fight. It suggests a place where one person's pace and the other's feelings can rub, which is useful to know before it happens on a tired Sunday evening. Difficult aspects describe pressure points, and pressure points can be talked about.

Try reading each hard contact as a pair of needs that both make sense. Person A's Leo Sun may want to be seen and appreciated out loud. Person B's Aquarius Sun may want room to think and act independently. Neither is wrong. The aspect only shows that the two needs sit at an angle and will sometimes ask for a conversation.

It also helps to remember that people grow, choose and learn. A chart describes tendencies and themes. How two people treat each other, and what they do when things go wrong, is not written in either chart.

Good Questions for a Couple to Ask About Their Synastry

Good questions are specific and point back to your daily life. “Our Moons are square. What might each of us need when we are stressed?” works better than “Are we compatible?” So does “Where might we misread each other's way of showing affection?” or “What does my Venus in your 11th house suggest about friendship between us?”

Ask from both sides. “How might this feel to me, and how might it feel to them?” is the kind of question the AI analysis is built to answer, because it rates each theme from each person's side. You can also ask what you share: “Which contacts suggest common hopes or goals?”

Questions about growth tend to give the most useful answers. “Which of these aspects could help us work through disagreements?” or “What strengths do we bring to each other?” keep the reading on patterns you can actually work with.

What an AI Compatibility Reading Should Never Tell You

An AI should not hand down verdicts such as “you're doomed”, “he's the one” or “this will end within a year”. It should not turn a relationship into a percentage or a probability of success, and it should not predict specific events, such as a breakup, a wedding or a date when something will happen. Cosine Astro's AI follows those boundaries: it talks about personality, feelings and relationship patterns, and the score out of 30 is a count of contacts that the AI does not convert into odds.

It also should not stand in for advice from a counselor, doctor or lawyer. If a relationship involves fear, control or harm, a chart is the wrong tool, and a trusted person or a professional is the right one.

General chatbots such as ChatGPT can talk fluently about synastry, but unless you paste in accurate positions they may guess the planets themselves and get them wrong. Here the positions are computed first, and the AI only interprets what was calculated.