The musica universalis (literally universal music), also called music of the spheres or harmony of the spheres, is a philosophical concept that regards proportions in the movements of celestial bodies – the Sun, Moon, and planets – as a form of music. The theory, originating in ancient Greece, was a tenet of Pythagoreanism, and was later developed by 16th-century astronomer Johannes Kepler. Kepler did not believe this "music" to be audible, but felt that it could nevertheless be heard by the soul. The idea continued to appeal to scholars until the end of the Renaissance, influencing many schools of thought, including humanism. History The concept of the "music of the spheres" incorporates the metaphysical principle that mathematical relationships express qualities or "tones" of energy which manifest in numbers, visual angles, shapes and sounds – all connected within a pattern of proportion. Pythagoras first identified that the pitch of a musical note is in inverse proportion to the length of the string that produces it, and that intervals between harmonious sound frequencies form simple numerical ratios. Pythagoras proposed that the Sun, Moon and planets all emit their own unique hum based on their orbital revolution, and that the quality of life on Earth reflects the tenor of celestial sounds which are physically imperceptible to the human ear. Subsequently, Plato described astronomy and music as "twinned" studies of sensual recognition: astronomy for the eyes, music for the ears, and both requiring knowledge of numerical proportions. Aristotle characterised the theory as follows: Aristotle rejected the idea, however, as incompatible with his own cosmological model, and on the grounds that "excessive noises ... shatter the solid bodies even of inanimate things", and therefore any sounds made by the planets would necessarily exert a tremendous physical force upon the body. Boethius, in his influential work De Musica, described three categories of music: musica mundana (sometimes referred to as musica universalis) musica humana (the internal music of the human body) musica quae in quibusdam constituta est instrumentis (sounds made by singers and instrumentalists) Boethius believed that musica mundana could only be discovered through the intellect, but that the order found within it was the same as that found in audible music, and that both reflect the beauty of God. Harmonices Mundi Musica universalis — which had existed as a metaphysical concept since the time of the Greeks — was often taught in quadrivium, and this intriguing