Comedian, theoretical physics grad and mathematics enthusiast Dara Ó Briain (@daraobriain) joins Matt and Andy to discuss stages of mathematical rigor, Évariste Galois, Catalina bison, Dara's new obsession with astrophotography from his London garden (examples of which are here and here), Andy's crappy cell phone moon pic and this podcast's new mission to help Dara get to Bortle 1. This episode is brought to you by The Great Courses Plus, offering Probably Science listeners a 14-day free trial with unlimited access PLUS 20% off when you sign up for an annual plan by visiting TheGreatCoursesPlus.com/probably