Galileo’s father, Vincenzo Galilei, is credited as one of the founders of the Italian opera and a major contributor to music theory. Johann Kepler formulated the harmonic law of planetary motions. The study of astronomy and music were deeply related in Galileo’s world.

According to the ancient Pythagoreans and many later writers, all of nature is a musical scale.  Music illuminated the study of astronomy, while astronomy provided a context for understanding music. Only through mathematics may nature be known.

In the Earth-centered model of the universe accepted during the Renaissance, a spherical Earth lies in the center surrounded by the regions of earth, water, air and fire.  Rotating heavenly spheres, nesting one within the other from the Moon all the way out, carry the planets and stars. A depiction of this is shown in Apian’s Cosmographia. As these solid celestial spheres turn in place, their harmonious motions create the music of the spheres.

Galileo gave lectures on Dante. Chaucer wrote a treatise on the astrolabe. Shakespeare and Galileo share the same birth year. Renaissance writers shared an intertwined literary and scientific heritage. Medieval and Renaissance works of literature are filled with the music of the spheres and the meaning of the planets.

During the century before Galileo, the three greatest works in astronomy were the Almagest edited by Regiomontanus, Copernicus’ De revolutionibus, and Kepler’s Mysterium cosmographicum, published exactly 100 years after Regiomontanus’ Almagest.

For thousands of years before the telescope, astronomers observed the stars and planets, predicting their movements and mapping locations on the surface of the Earth. The astronomer’s toolkit contained remarkably capable instruments, including the sundial, astrolabe, celestial sphere, armillary sphere, quadrant, sextant and orrery.