Tuning the Sky

The ancient Pythagorean notion of a musical universe sounds quaint today, but it was still very much a live option during the era of the scientific revolution. David Plant explains how Kepler’s laws of planetary corresponded to the intervals of music:

“Kepler’s First Law states that the planets move in ellipses and that the Sun is not at the exact centre of their orbits. Each planet moves between a ‘perihelion’ point nearest the Sun and an ‘aphelion’ point furthest away. The Second Law states that the planets move faster at perihelion than at aphelion. Kepler measured their angular velocities at these extremes (i.e. how far they travel in 24 hours in minutes and seconds of arc as viewed from the Sun) and expressed this ratio as a musical interval. Saturn, for instance, moves at a rate of 106” per day at aphelion and l35” at perihelion. Cancelled down, the ratio 106:135 differs by only two seconds from 4:5 — equivalent to the interval of a major third. Kepler found that the angular velocities of all the planets closely correspond to musical intervals. When he compared the extremes for combined pairs of planets the results were even more marvellous, yielding the intervals of a complete scale. Thus, the ratio between Jupiter’s maximum and Mars’ minimum speed corresponds, to a minor third; the interval between Earth and Venus to a minor sixth. Rather than the fixed-tone planetary scales of earlier schemes, Kepler’s measurements revealed ever-changing polyphonic chords and harmonies as the planets move between perihelion and aphelion. Furthermore, he had shifted the focus of celestial harmony from the Earth to the Sun: ’ Henceforth it is no longer a harmony made for the benefit of our planet, but the song which the cosmos sings to its lord and centre, the Solar Logos .’”