The Sacred Calendar and Venus

The following ways of counting the days were used in ancient Mesoamerica: the 360-day tun; the 365-day 'vague year'; the synodic period of Venus which was approximated by 584 days; and a cycle of 260 days, the so called Sacred Calendar. I While the first three have a direct astronomical association.? the lastmentioned lacks such an interpretation. Longer periods were, of course, constructed by combining these basic periods, and some of these were used in turn to represent astronomical phenomena. However, it seems plausible that they were secondary applications of a cycle that was already established. In the words of Thompson.' "I should regard the cycle of 260 days as being of considerably greater age than the completed calendar. It is very widely distributed in Central America, and in most areas it has more mythological and ritualistic associations than the year of 365 days." The analogy with our own calendar (as, for example, in our week) suggests the possibility that elements stemming from an earlier era of astronomical knowledge could later be found to be insufficiently exact, but could continue to be respected as an ancient tradition and gradually take on a more ritual character. Therefore in our view the following question is meaningful: Can we find a simple astronomical interpretation of the 260-day cycle which could have been in use before the Maya calendar was fully elaborated? In this paper we postulate that this cycle had a connection with the planet Venus. The planet Venus and especially its heliacal rising as a morning starplayed a central role in ancient Mesoamerica. 4 Yet its synodic period, 584 = 8 x 73 days, involved the prime factor 73, which would not have been easy to