Time human or time divine: theological aspects in opposing the Gregorian calendar reform

On 24 February 1582, Pope Gregory XIII issued a Bull, inter gravissimas, initiating the reform of the Julian Calendar. Whilst the new Gregorian Calendar was adopted by the majority of Catholic states, it was rejected by most Protestant states. Focusing on the treatises written by the theologian Jacob Heerbrand and the mathematician and astronomer Michael Maestlin, this article considers the arguments used against adopting the calendar, and in particular the way in which theological arguments were applied to this question, not, at first sight, a theological issue at all