Note to Twelfth Night, 3.1.110, "music from the spheres"

The moon, the sun, Venus, Mars, and all the heavenly bodies were believed to be embedded in crystalline spheres, each one contained within the next larger one, up to the ninth sphere, the abode of God. The motion of these spheres was believed to produce a heavenly harmony which we cannot hear because we are mere mortals. In The Merchant of Venice a character looks up at the night sky and says to his beloved, "There's not the smallest orb which thou behold'st / But in his motion like an angel sings" (5.1.60-61).

Illustration of the Celestial Spheres, 1377