Synastry

Meaning

Synastry sets two birth charts side by side and reads how they meet. It looks at two things. First, the aspects between one person’s planets and the other’s: where one person’s Moon falls in trine to the other’s Venus, or one’s Saturn squares the other’s Sun. Second, the house overlays: in which of one person’s houses the other’s planets land.

Each contact is read in both directions. When your Mars sits on someone’s Moon, your drive touches their feelings, and their feelings colour how your drive is met. A harmonious contact is read as ease and recognition, a tense one as friction that can also bring growth. No chart pair is all ease, and many lasting bonds rest on a few strong tensions worked through together.

Synastry describes a meeting of temperaments, not a verdict. It shows where two people understand each other without words, and where they will need patience, words and time. It serves friendship, family and work as well as love.

In practice

• Sun and Moon: one person’s Sun on or in aspect to the other’s Moon is the classic contact of companionship, read as a sense of being understood and of fitting together.
• Venus and Mars: contacts between one’s Venus and the other’s Mars are read as attraction and spark; Venus to Venus as shared taste.
• Saturn contacts: one person’s Saturn on the other’s personal planets is read as commitment and seriousness, sometimes as weight. Many long relationships hold one.
• House overlays: someone whose planets fall in your 7th house is read as a natural partner figure for you; in your 10th, as someone who touches your public life or calling.
• The angles: a planet of one chart on the other’s Ascendant or Midheaven makes a contact that is felt quickly and plainly.

Across traditions

• Indian astrology compares two charts above all through the Moon’s lunar mansions, the nakshatras: the ashtakoota method scores eight factors for a total of 36 points.
• Chinese astrology reads the animals of the two birth years: those of one triangle, such as the Monkey, the Rat and the Dragon, are said to agree, while opposite animals, such as the Rat and the Horse, are said to clash.
• Numerology compares the two life paths and the numbers of the names.

Origin and history

Comparing charts is ancient. In the Tetrabiblos (2nd century), Ptolemy, writing on marriage, reads the Sun and the Moon of one chart against those of the other: when the lights of the two charts are in harmonious aspect, he expects a lasting bond. The word synastry comes from the Greek syn, together, and astron, a star. In the twentieth century, synastry grew into a large field of its own, with the composite chart added beside it.

How Ulune calculates it

• Every body and point of each chart, with its four angles, is set against every body, point and angle of the other. Each pair keeps the one aspect closest to exact.
• Synastry uses its own orbs, a little tighter than a birth chart’s: 6° for the conjunction, opposition, trine and square, 4° for the sextile. One degree more is allowed when the Sun or the Moon is involved, for those five aspects.
• To an angle, an orb is never wider than in a birth chart: 6° for a trine and 4° for a sextile.
• The minor aspects are kept tight: 2° for the quincunx, 1.5° for the semi-sextile, the semi-square and the quintile.
• The house overlays place each person’s bodies and angles in the other’s houses, with the house system of the chart they fall into.
• When either birth time is unknown, the overlays are noon stand-ins and marked so. When a chart has no usable houses, Ulune shows no overlay into it rather than placing everything in the first house.