Synastry: Compare Two Birth Charts

What synastry actually is

Synastry is the astrology of relationships between two specific people. Instead of reading one chart on its own, an astrologer compares two natal charts to see how one person's planets interact with the other's — where the energies harmonize, where they grind, and where each person activates something in the other that lies dormant otherwise.

This is a different question from "are Leos compatible with Scorpios?" Sun-sign compatibility compares two twelfths of humanity; synastry compares two individuals, with all ten planets, the angles, and the houses of each chart in play. Two people with "incompatible" Sun signs can have a beautifully interlocking synastry, and vice versa.

Synastry does not score a relationship as good or bad. Read well, it describes the texture of a connection: what feels effortless, what needs negotiation, why certain arguments repeat, and what each person is likely to draw out of the other over time.

How synastry works: inter-chart aspects

The core technique is the inter-chart aspect: measuring the angles between one person's planets and the other's. If your Venus sits at 12° Cancer and your partner's Mars at 14° Cancer, that is a tight Venus–Mars conjunction between your charts — classically one of the strongest attraction signatures in synastry.

The same aspect vocabulary from natal astrology applies, but across the pair. Conjunctions fuse two people's planetary functions; trines and sextiles let them cooperate easily; squares and oppositions create friction that can be erosive or generative depending on the planets involved and the people living it. Astrologers typically weight contacts involving the personal planets (Sun, Moon, Mercury, Venus, Mars) and the chart angles most heavily, because those describe day-to-day chemistry rather than generational background.

• ✦Sun–Moon contacts: the classic mutual-recognition signature between charts
• ✦Venus–Mars contacts: attraction and romantic chemistry
• ✦Mercury contacts: how easily two people understand each other
• ✦Saturn contacts: commitment and durability — or restriction, by aspect
• ✦Aspects to the Ascendant: immediate, visceral first-impression pull

House overlays: where their planets land in your life

The second core technique is the house overlay: taking one person's planets and placing them into the other person's houses. Your houses are the map of your life's arenas — money, communication, home, partnership, career — so where someone's planets fall in that map shows which parts of your life they light up.

A partner whose Sun lands in your 7th house feels like partnership material almost by definition; a partner whose Mars lands in your 10th house energizes (or agitates) your career and ambitions. Overlays are directional, too: their Moon in your 4th house and your Moon in their 11th house describe two different experiences of the same relationship, which is often exactly where the interesting asymmetries live.

Because houses depend on birth time, good synastry needs accurate birth times for both people — the same rule as any natal chart, doubled.

What MySkyChart offers today — honestly

Straight answer: MySkyChart does not yet have a dedicated synastry tool. We would rather tell you that plainly than ship a compatibility-score gimmick, and a proper synastry feature — inter-chart aspects and house overlays, interpreted with the same placement-level care as our natal readings — is on our roadmap.

What you can do today is the genuine first half of synastry: create accurate natal charts for both people. Each chart is free, calculated with the Swiss Ephemeris to exact degrees, with houses and aspects included, and with a free account you can save multiple charts side by side — yours and your partner's.

Each of you can also get a reading. Understanding your own Moon, Venus, and Mars — and your partner's — is not a consolation prize; it is the foundation every competent synastry reading is built on. An astrologer always reads both natal charts before comparing them, because a person's relational patterns are visible in their own chart first.

When the synastry tool ships, the charts you create now will be ready for it — same account, same data, no re-entering birth details.

Start the comparison yourself

You can get surprisingly far by hand with two charts open. Look up each person's Sun, Moon, Venus, and Mars signs and check the element relationships: same element flows, complementary elements (fire–air, earth–water) cooperate, and the rest is where the interesting friction lives.

Then go one level deeper with degrees, since both charts list them: two planets within a few degrees of each other in the same sign are conjunct across the charts; roughly 90° apart is a square; roughly 120° a trine. Even spotting three or four tight inter-chart aspects this way will tell you more about the relationship than any Sun-sign table, and our aspects guide covers what each one means.

Frequently asked questions