This dissertation is focused on the 3rd C. BC Hellenistic poet Aratus and his astronomical poem, the Phaenomena. While the Phaenomena once enjoyed a vast circulation and celebrity in antiquity, among modern readers it has had a much-diminished reception, and this disparity has been the crux of considerable debate. The poem appears catalogic in nature, listing constellations one after the other with momentary diversions into mythological embellishment. The accuracy of the astronomical details in the poem have been questioned, even in antiquity, and it has been generally accepted that Aratus was not himself expert in astronomy but was merely adapting the prose scientific treatises of Eudoxus of Cnidus (c. 390 – c. 340 BC) into verse with perhaps modest modifications. Recently, however, there has been a resurgence of interest in rehabilitating the reputation of Aratus as a capable astronomer, of which this project is part. My approach has been to consider the poetic wordplay and mythological elements of the poem not as moments of distracted levity or relief from a more technical and scientific narrative, but as themselves demonstrative of astronomical theory. In addition to tracing the conceptual status of constellations in Ancient Greece, this dissertation establishes the existence of a much larger body of uniquely Aratean astronomical theory than has previously been imagined and demonstrates the capacity of poetic language for the expression of scientific and philosophical thought among Hellenistic and later poets.