As the Romantic biographer Richard Holmes has noted, ‘the very terms “world” and “universe” began to change their meanings’ during John Keats’s lifetime. In papers published in the Philosophical Transactions of the Royal Society between 1780 and 1814, the astronomer William Herschel identified a vast and unwieldy universe filled with millions of star laboratories – galaxies of nebulous matter and stars existing in various stages of development formed under the universal force of gravity. Stellar material was in flux and stars could no longer act as sublime metaphors for permanence and constancy. The simple yet dangerous idea that the universe, in its entirety, undergoes change, found its way into the intellectual culture of Keats’s time. While some writers attempted to resolve this cosmological confusion by emphasising the unity and cohesion of the cosmos, Keats recognised the fertility of this new cosmological model and incorporated it into his poetry. According to Marilyn Gaull, Romantic astronomy ‘did not find its voice in art or literature, except in the mythic representations of Blake and Shelley.’ It is the purpose of my research to disprove or at least complicate this statement. My thesis will discuss, not only how contemporary scientific debate found its way into Keats’s writing, but how he was able to take up his poetic inheritance by acting, like Ovid, Shakespeare and Milton before him, as interpreter or interlocutor, between scientific and popular understandings of contemporary astronomy. By contemplating the intricacies of Herschel’s work, especially the nebulosity of his theories on the ‘construction of the heavens’ and the paradox of eternity that rests at the heart of his cosmology, this thesis contains an in-depth study of the science and scientific discourse, as well as the poetry of the period. Paying particular attention to Keats’s cosmological writing – those poems interested in the relation between heavenly and earthly realms, namely ‘On First Looking into Chapman’s Homer,’ ‘Bright Star,’ Endymion and Hyperion: A Fragment – as well as the representation of contemporary astronomy in Romantic-era print culture, my thesis argues that Keats’s poetry contains a sensitive response to the complications posed by science to mythical and biblical ideas of permanence, universalism and eternity.