American Aurora explores the impact of climate change on early modern radical religious groups during the height of the Little Ice Age in the seventeenth century. Focusing on the life and legacy of Johannes Kelpius (1667-1707), an enormously influential but comprehensively misunderstood theologian who settled outside of Philadelphia from 1604 to 1707, Timothy Grieve-Carlson explores the Hermetic and alchemical dimensions of Kelpius's Christianity before turning to his legacy in American religion and literature. This engaging analysis showcases Kelpius's forgotten theological intricacies, spiritual revelations, and cosmic observations, illuminating the complexity and foresight of an important colonial mystic. As radical Protestants during Kelpius's lifetime struggled to understand their changing climate and a seemingly eschatological cosmos, esoteric texts became crucial sources of meaning. Grieve-Carlson presents original translations of Kelpius's university writings, which have never been published in English, along with analyses and translations of other, important sources from the period in German and Latin. Ultimately, American Aurora points toward a time and place when climate change caused an eruption of esoteric thought and practice-and how this moment has been largely forgotten.