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

The so-called Miccinelli documents are secret manuscripts which were written by Jesuit scholars in Peru within the first half of the 17th century. Among such documents, one contains the diagrammatic depiction of a Khipu, which 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 data reported in this document, showing that they actually correspond closely to the astronomical events occurred in Cusco in that year. Further, we 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. We also discuss the relationship of the data with known pre-conquest sources - both of documental and of archaeo-astronomical type - about Inca calendrics and astronomy. Finally, the possible relevance of the document for the knowledge of the original Inca lore of the sky is discussed in details.