What was the comet depicted in Giotto’s Adoration of the Magi?

A minor but enduring mystery in art history is the identity of the comet depicted in Giotto di Bondone’s work The Adoration of the Magi, painted as a fresco in the Scrovegni Chapel in Padua. Representing the Star of Bethlehem and traditionally assumed to be inspired by an object personally observed by Giotto, it has been associated with 1P/Halley’s 1301 return. However, this identification has been questioned. The apparition was theoretically a poor one, with closest approach to Earth being before perihelion and the calculated magnitude always fainter than +1, although there is some evidence that the comet was brighter than would be expected from its average activity over two millennia. An alternative inspiration would be one of the two comets observed in 1304: C/1304 C1 and the 1304 Christmas Comet, C/1304 Y1. The former was observed for two and a half months, between February and April. The latter was observed for just six days but, critically, these included Christmas Eve and Christmas Day, which would have been significant to a devout catholic such as Giotto. This paper examines the three principal candidates and their visibility in detail, plus other comets that were reported in the 1300–1306 time frame. While C/1304 Y1 appears to be a likely model for Giotto’s work, significant questions remain about all three candidates.