Music of the Spheres

Music of the Spheres

Ptolemy’s aetherial spheres, imagined in medieval times to be made of crystal, are why we still talk about the music of the spheres and a seventh heaven (there was a “heaven” or sphere for the Moon, Mercury, Venus, the Sun, Mars, Jupiter and Saturn, and one for the stars).

In fact, every culture has leaped to the geocentric hypothesis. As Johannes Kepler wrote, “it is therefore impossible that reason not previously instructed should imagine anything other than that the Earth is a kind of vast house with the vault of the sky placed on top of it; it is motionless and within it the Sun being so small passes from one region to another, like a bird wandering through the air”. But how do we explain the apparent motion of the planets – Mars, for example, which had been known for thousands of years before Ptolemy’s time?

With the Earth the center of the Universe, with creation pivoted about terrestrial events, with the heavens imagined constructed on utterly unearthly principles, there was little motivation for astronomical observations. Supported by the Church through the Dark ages, Ptolemy’s model helped prevent the advance of astronomy for a millennium. Finally, in 1543, a quite different hypothesis to explain the apparent motion of the planets was published by a Polish Catholic cleric named Nicholas Copernicus. Its most daring feature was the proposition that the Sun, not the Earth, was at the center of the universe. The Earth was demoted to just one of the planets, third from the Sun, moving in a perfect circular orbit (Ptolemy had considered such a heliocentric model but rejected it immediately; from the physics of Aristotle, the implied violent rotation of the Earth seemed contrary to observation).

The Earth Seen From the Moon. Our home planet is a large sphere rotating at the sound of music. Image : Illusion © Meg Jorgensen (Elena)

In Ptolemy’s Earth-centered system, the little sphere called the epicycle containing the planet turns while attached to a larger rotating sphere, producing retrograde apparent motion against the background of distant stars.

In Copernicus system, the Earth and other planets move in circular orbits about the Sun. As the Earth overtakes Mars, the latter exhibits its retrograde apparent motion against the background of distant stars.

It worked at least as well as Ptolemy’s spheres in explaining the apparent motion of the planets. But it annoyed many people. In 1616 the Catholic Church placed Copernicus’ work on its list of forbidden books “until corrected” by local ecclesiastical censors, where it remained until 1835 (in a recent inventory of nearly every sixteenth-century of Copernicus’ book, Own Gingerich has found the censorship to have been ineffective: only 60 percent of the copies in Italy were “corrected”, and not one in Iberia.