Sun Trine Mercury Synastry: When Who One of You Is and How the Other Talks Share a Language

In synastry, each person's birth chart is set beside the other's. Here the Sun in one chart, which stands for who a person is (their core, their values, the direction they tend to take), meets Mercury in the other, which stands for how a person thinks and talks (word choice, questions, the way they explain, listen and joke). The two are about 120° apart, a third of the way round the zodiac.

A trine usually joins two signs of the same element: fire with fire, earth with earth, air with air, water with water. (Usually, not always: a trine that starts near the edge of a sign can reach into the next element.) That is the geometry. The reading built on it is likeness: the way one of you is and the way the other talks may come from the same kind of temperament, whether that is lively, practical, curious or tender. It is not the very same spot, as in a conjunction, but the same kind of spot.

So the way one of you talks may need little translation for the other, and the way one of you is may be easy for the other to describe.

Friends, siblings, colleagues, classmates, a parent and their child, and partners can all share this contact, and it is one contact among many in any two charts.

In this contact one of you brings the Sun and the other brings Mercury, and the two of you are in the same element. Call them the Sun person and the Mercury person.

If you are the Sun person, you are going about your own business: following what interests you, choosing how to spend the day. Around the Mercury person you may find you are easy to follow. What you say about yourself may be taken in as you meant it, and you may need to explain less than usual.

If you are the Mercury person, you are thinking aloud, asking, explaining, passing on what you have noticed. Around the Sun person your words may go through with little friction. You may say plainly things you would soften elsewhere.

If the link also runs the other way, from the Mercury person's Sun to the Sun person's Mercury, each of you is both.

In a trine, being and saying may run with little resistance, because both come from the same element.

The Mercury person may give the Sun person a sense of being followed: what the Sun person says about themselves can be met with a reply close to what they hoped for, put in words they would have chosen.

The Sun person may give the Mercury person a listener who keeps up. Ideas, jokes and half-formed thoughts may be taken up readily, so the Mercury person can think aloud with less checking of every phrase.

At different moments each of you is the one followed and the one following. Either of you may want to be asked and not only understood, since ease can make a question seem unnecessary. Either of you may also want a remark taken seriously and not only comfortably.

These are sketches, not reports: illustrations of how a shared language might show up across different kinds of pairs.

• Students. Two students wait outside a lecture hall. One mentions, in a sentence, that they are thinking of a year abroad. The other's reply is the one they would have written for themselves.
• Referees. Two referees at a youth match walk off together. One begins to say how the game went, and the other nods before the sentence is done, because the summary was already theirs.
• Flatmates. One flatmate says the hallway needs a coat rack. The other has already measured the wall and says the number, in much the same tone.
• Aunt and niece. An aunt and a grown niece are halfway through a crossword. One reads a clue; the other fills in the answer before the clue is finished, and neither remarks on it.
• Friends. One friend says they are tempted to repaint their front door. The other says "yellow", and it is the colour the first had been picturing.

In each sketch how one person is and how the other puts things point the same way.

A trine usually joins two signs four apart, which share an element and belong to different modes. (The twelve signs fall into three modes by how they move: cardinal signs start things, fixed signs keep them going, mutable signs adapt as they go.) Aries and Leo, for instance, are both fire, one cardinal and one fixed. So the two of you share an element, and may differ in how that element moves. In plain terms: fire is enthusiasm and action, earth is practical steadiness, air is talk and ideas, water is feeling.

Fire. Both are bold and direct. The Mercury person's way of speaking may suit the Sun person's confidence. It might look like two stagehands before curtain-up, one calling the layout and the other already carrying the crates.

Earth. Both value plain, exact speech. The Mercury person says what is so, and the Sun person is steady in being so. It might look like two joiners who settle a measurement in one sentence and both think it the best conversation of the week.

Air. Both enjoy ideas for their own sake. The Mercury person follows a thought wherever it goes and the Sun person is curious enough to go along. It might look like two travellers at an airport gate who begin by comparing book recommendations and finish by drafting a list for a reading group.

Water. Both speak from feeling and memory, and the words carry a mood the other recognises. It might look like two old friends cooking a dish from childhood, each naming the next ingredient before the other can.

One thing this contact can give is how simple it is to be understood and to understand. It can also have a quieter side, which belongs to this pair of planets.

Because the words already fit, a question may seem unnecessary. Each of you may take the other's view for granted, and a difference, when there is one, may take a little longer to come out because nothing prompted it.

Because talk is comfortable, a disagreement may be slow to surface from either side. A remark that sits well with both of you is not always one each of you holds, and an easy agreement can stand in for a conversation.

Taken together, it is a smooth contact, and sometimes a quiet one about the questions it does not need to ask.

Two passages in the older sources used here name the Sun with Mercury in an aspect: William Lilly's (*Christian Astrology*, 1647, Book III, p. 638) and James Wilson's (*A Complete Dictionary of Astrology*, 1819, p. 381). Neither passage says anything about the trine. The only aspect either names is the opposition. Lilly's page also has a line on the Sun and Mercury standing in each other's places, which is not an aspect and is not used here. So nothing from the older sources is used for this contact.

The distinction this page draws, that a trine reads as likeness because it usually joins signs of the same element, is based on the kinds of sign a trine usually joins. It is an editorial reading, not something the older books say about the Sun and Mercury. The same goes for everything else on this page: who the Sun person and the Mercury person are, what each gives and may want, the element variations and the sketches, which are illustrations.

• One of you can say it in one go, and the other may follow.
• You may have found yourselves easy to talk to soon after you met.
• Messages between you may be short and still understood.
• One of you has finished the other's sentence with the right ending.
• Now and then something is agreed so quickly that neither of you is sure it was discussed.