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On the music of the spheres
Boethius sorted music into three kinds: musica instrumentalis , the kind you can play; musica humana , the harmony of body and soul; and musica mundana , the music of the cosmos itself. This page tries to turn the third into the first.
What you are hearing
A planet sings each time it crosses a brass needle. Its pitch is its angular speed at that moment, meaning how fast it sweeps around the star, transposed up many octaves until you can hear it. A planet on the 1:1 ring sings the root note. One that laps twice as fast sings an octave higher, and three times as fast an octave and a fifth.
On an ellipse a planet speeds up near the star and slows down far from it, so it sings a different note at each needle: a melody. Kepler worked that out four centuries ago.
Kepler’s planets
In Harmonices Mundi (1619), Johannes Kepler compared each planet’s angular speed at its farthest point from the Sun with its speed at its nearest, and heard intervals:
Planet Slowest : fastest Interval
Saturn 4 : 5 major third Jupiter 5 : 6 minor third Mars 2 : 3 fifth Earth 15 : 16 semitone Venus 24 : 25 diesis Mercury 5 : 12 octave and a minor third
Earth only moves between mi and fa , from which, Kepler wrote, you might guess that mi sery and fa mine hold sway on our home. The same book announced his third law: the square of a planet’s period grows with the cube of its distance. That law sets every rhythm on this page. Open Kepler’s choir to hear the inner planets with their real eccentricities.
Where the rhythm comes from
When two orbital periods form a simple ratio, the planets keep returning to the same arrangement, and the pattern of notes repeats. That is a polyrhythm. The dashed rings mark those ratios against a measure of four beats: a planet on the 3:2 ring crosses each needle three times every two measures. With Resonance on, new orbits snap to these rhythms, elliptical ones included.
Nature does this too. Io, Europa and Ganymede circle Jupiter in a 1:2:4 chain called the Laplace resonance, and Pluto goes around the Sun twice for every three orbits of Neptune.
TRAPPIST-1
In 2017 astronomers announced seven Earth-sized planets around TRAPPIST-1, an ultracool red dwarf about 40 light-years away. Their years last from 1.5 to 18.8 days, and neighbouring planets orbit in ratios close to 8:5, 5:3, 3:2, 3:2, 4:3 and 3:2. That makes it one of the longest resonant chains known. The chain is probably a fossil of the planets migrating inward together, and it may be what keeps such a crowded system stable. The preset uses their measured periods in pure tuning, so the chord you hear is theirs.
How to play
Click Set a planet in a circular orbit
Drag Fling a planet. The dashed path previews the notes it will sing
Click a planet Pluck it
Drag a planet Move it, or drop it into the star or off the rim to remove it
Right-click Remove a planet or a needle
Drag a knob Swing a needle around the rim
Click the star Change the star, which also colours the sound
1 –6 Choose a voice
[ ] Planet size
Space Pause time
↑ ↓ Tempo
R G Resonance, mutual gravity
N ⇧N Add or remove a needle
Z Take back the last planet you added
V M Night or vellum plate, mute
Every sound is synthesised live with the Web Audio API and every line is drawn on a canvas. No samples, no accounts, no cookies. Visits are counted anonymously, and your last sky is kept in this browser only.
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