A calendar Quipu of the early 17th century and its relationship with the Inca astronomy

The so-called Miccinelli documents are a set of documents which were written by Jesuit scholars in Peru within the first half of the 17th century. Among such documents, one contains the depiction of a Quipu, that is, a device made out of cords of different nature and colors which, with the help of nodes, were used by the Incas for storing data. This Quipu is claimed by the author, Blas Valera, to be a reproduction of the Inca calendar of the year of the Spanish conquest. We give here a complete analysis of the astronomical events occurred in Cusco in that year, showing that they actually correspond closely to the data reported in the Quipu, and compare the calendrical information - such as the names and the rituals of each month - with those given by other documents, especially the Nuova Coronica by G. Poma de Ayala. The possible relevance of the document for the knowledge of the original Inca lore of the sky is discussed in details.