Johannes Kepler accepted Tycho Brahe’s claim that the Copernican hypothesis required all stars to be giant, something Brahe found absurd. Kepler argued in his De Stella Nova that some stars were larger than Brahe’s size for the entire universe. He also used the issue of star sizes to argue against Giordano Bruno’s infinite universe. Kepler’s acceptance of Brahe’s ideas on star sizes appears in a variety of his writings, including his response to the anti-Copernican essay by Msgr. Francesco Ingoli that cited the star size issue, an essay Galileo had felt was influential in the rejection of the Copernican hypothesis by authorities in Rome in 1616. Kepler’s writings illustrate how certain supporters of Copernicus viewed the universe of stars and relied on divine power to undergird that view. Decades after Kepler, the discovery that the star size problem rested on a formerly unrecognized optical effect both freed the Copernican hypothesis from Brahe’s charge of absurdity and negated Kepler’s argument against Bruno.