Music of the spheres
An ancient idea that the movement of the celestial bodies produces sounds, still received today as a musical-philosophical motif.
What it means
The music of the spheres (Latin musica universalis) is an ancient idea holding that the movement of the celestial bodies itself produces sounding tones that combine into a cosmic harmony. This "music," however, is not audible to the human ear.
The idea is associated above all with Pythagoras and the Pythagorean school, which suspected a connection between the numerical ratios of musical intervals and the distances or orbital periods of the planets.
Musical use
In antiquity and the Middle Ages, the music of the spheres was often understood as the highest of three levels of music, above audible instrumental and vocal music and the inner harmony of the human body, as in Boethius's division into musica mundana, musica humana, and musica instrumentalis.
As an actual, acoustically describable sound phenomenon, the music of the spheres has no scientific basis; but it was repeatedly taken up as a philosophical and poetic motif, for instance by Kepler, who related planetary motion to musical ratios, as well as in literature, the visual arts, and occasionally in music itself as an allusion.
The music of the spheres should be distinguished from actually audible instrumental and vocal music, and from modern, purely metaphorical uses of the term that no longer relate to the original cosmological theory.
Performance practice
If you encounter the term music of the spheres in a work's title or program note, take it as an allusion to this old, symbolically intended idea of cosmic harmony, not as a description of an actually audible sound.