"It’s hard to imagine the thrill and surprise Galileo must have felt when he first looked up with his..."

It’s hard to imagine the thrill and surprise Galileo must have felt when he first looked up with his new instrument and gazed upon the heavenly bodies— described for centuries as the revolving spheres of the moon, sun, and planets. Beyond were the revolving crystalline spheres holding the stars, and finally the outermost sphere, the Primum Mobile, spun by the finger of God. All of it supposedly constructed out of aether, Aristotle’s fifth element, unblemished and perfect in substance and form, what Milton described in Paradise Lost as the “ethereal quintessence of Heaven.” And all of it at one with the divine sensorium of God. What Galileo actually saw through his little tube were craters on the moon and dark acne on the sun…

I want to focus now not on the displacement of earth as the center of the cosmos but on the newly conceived materiality of the heavens. Because it was that materiality, that humbling of the so-called heavenly bodies, that struck at the absolute nature of the stars. The demotion started with the observed craters and ruts on the moon… it was for the nature of stars that Galileo’s findings had perhaps their most profound impact […] 

Thus, when Galileo reported blemishes on the sun, his findings had dramatic implications for all of the stars. The stars could no longer be considered perfect things, composed of some eternal and indestructible substance unlike anything on earth. The sun and the moon looked like other material stuff on earth. In the 1800s, astronomers began analyzing the chemical composition of stars by splitting their light into different wavelengths with prisms. Different colors could be associated with different chemical elements emitting the light. And stars were found to contain hydrogen and helium and oxygen and silicon and many of the other common terrestrial elements. Stars were simply material—atoms.