your chart, as a chord

how it works

The twelve signs become the twelve notes, and each planet plays the note of the sign it was in when you were born. The Sun's note is the root of the chord.

Either way round the wheel, the zodiac's own groupings turn into the symmetric chords of music. Signs of one element (a trine) form an augmented triad. Signs of one modality (a square) form a diminished seventh. Opposite signs are a tritone, and every other sign (a sextile) is a whole tone.

Circle of fifths starts Aries on C and steps up a fifth per sign, so neighbouring signs are the most consonant interval. Each planet's degree nudges its note only a few cents, a light shimmer.

Chromatic · musical astrology follows the Musical Astrology system: Aquarius on C and a semitone per sign. A sign spans 100 cents over 30°, so every degree is 3.33 cents and the exact note sits at 15°. Pitch then flows continuously around the whole sky, and most planets land between two notes, in the microtonal space between the keys.

The root is the Sun unless you give a birth time. With a time, the root becomes your Ascendant, the degree of the zodiac rising on the eastern horizon at the moment you were born. It changes sign about every two hours, so the same planets can sound like a quite different chord over a different bass. The Ascendant also depends on where you were born: pick the city nearest your birthplace in the list next to the time.

Voicing decides which octave each planet sings in. Sun root puts the Sun in the bass as the chord's root, Venus on top, and the slow outer planets as a quiet shimmer above. Slow = low follows Kepler's planetary choir in Harmonices Mundi (1619): the slower a planet moves, the lower it sings. Pluto, Neptune and Uranus are the bass, Saturn and Jupiter the tenor, Mars, the Sun, Venus and Mercury the alto, and the Moon the soprano. The notes stay the same either way; only their octaves change.

Aspects are counted by whole sign, the way Hellenistic astrologers did, so each aspect line on the wheel is also an interval in your chord. Traditional astrology recognised only Ptolemy's five: conjunction, sextile, square, trine and opposition. Signs one or five apart, the semi-sextile and quincunx, were said to be in aversion: they can't see each other. This page follows that tradition: those pairs are marked "in aversion" and get no aspect line.

Pythagorean is the circle of fifths built the ancient way, from perfectly pure 3:2 fifths, the tuning behind the old idea of the music of the spheres. Every step between neighbouring signs is a pure fifth, and thirds come out bright and wide. But twelve pure fifths overshoot the octave by a sliver (the Pythagorean comma, 23.5 cents), so one fifth has to absorb it: the sour wolf between Pisces and Aries, where the zodiac year fails to close.

Either way, starting on C is only a convention. The chord's character comes entirely from where your planets sit relative to your Sun.

Without a birth time the Moon is placed at noon, so a Moon that changed sign that day may be one note off.