Celestial waltz

Abstract

Playing the keys of a piano at random results in discordant sounds, but once the same notes are rearranged following harmonic laws, a melody is born. The ancient dream of celestial mechanics was to discover the ‘music of the spheres’ — the harmony hidden behind the motion of the planets as a sign of God’s creation. Indeed, the development of astronomy showed that the Solar System is much more complex than previously thought. Besides the planets there are satellites, comets, asteroids, rings, and, as has been discovered in recent times, a whole new population of icy bodies orbiting beyond Neptune. Yet the motion of all these different celestial bodies is far from a random wandering in space, since in many cases they are ‘tuned’ in a sequence of harmonic chords. According to modern celestial mechanics one can say that the music of the heavens is a concert in which peculiar configurations — orbital resonances — play the main theme.