This unique collaboration between a classicist and physicist at the University of Illinois at Chicago is the first work to combine the evidence from both China and Rome for the spectacular daylight comet of 44 BC, perhaps the most famous comet in antiquity. This investigation, which also examines allusions to this comet in astrological literature from later antiquity, sheds new light on the significance of the comet as a powerful symbol in the political propaganda that launched Augustus’ career.