One of the most important problems of astronomy and Inca calendar involves an evaluation of the identities and role of the Pucuy and Chirao sucancas. There is a lot of pertinent and conclusive ethnohistorical information about these, but this information is scattered. In addition, the Spanish informants confused their importance and nature.
Recall that Polo gave no indication of where the sucancas Pucuy and Chirao should have been, or what dates they represented. In addition, many do not accept the dates of Cobo, nor that the sucancas near the hill Mutu or the Quincalla are the respective sucancas Pucuy and Chirao. However, Cobo was right, that these represented dates, half a year away from each other.
We know from these writings that the Eastern Sucanca near Quispicancha had an important role in November. This was probably an observation of the sunrise in a significant astronomical event seen from the area of Cuzco. The pillars of Cerro Sucanca were used to observe a sunset in August from the main plaza of Cusco, but with an astronomical purpose unknown. In addition, it is believed that a connection between Cusco and Quispicancha was used for two different types of observations, one towards and the other from Quispicancha.
Perhaps the most important public solar observations, observed by all the population of Cusco, were realized at the times of tilling and sowing. At that time, observations were made from the main square of the Cusco as the setting sun passed over about a month using a system of four pillars placed on the western horizon. Only one chronicler (Cieza de Leon) wrote what he really saw in 1551. And, the Anonymous chronicler gave precise details of the distance between the pillars and the observer.
Observations towards the hill Sucanca were made by two groups: one of the priests from Quispicancha Sucanca and by the common people from the greater place of Cusco. Both groups looked in the same direction though the priests looked at the mountain itself and the common people at the pillars.
We can conclude that solar observations as we find them among the different writings of the chroniclers are not a random collection, but rather belong to a well-organized system. However, it is difficult to understand this system in terms of an organization of the Inca months. They do not map onto each other easily.