The Mayas were fascinated of the time and the heaven. They developped one of the most precise calendars which existed in those days. Because of precises observations, the Maya priests had astonishing astronomical knowledge (the best in those days). They calculated the sunyear, solar and lunar eclipses, rising and sinking of the Venus, movements of the stars and planets, ... Researchers today still are astonished about the exactness of these calculations. But they only were possible because the Mayas could handle with very high numbers. They did not use a decimal but a vigesimal system, that means that the number 20 was the basis of their arithmetical system. So they could calculate and symbolize without problems unbelievable high numbers. The Mayas also knew the number 0.
Although the Mayas had calculated the sunyear of 365 days (divided up in 18 months with 20 days and 1 month with 5 days), the so called ritual calendar was more important for them. It contained only 260 days and was used to find out the best days for different intentions and activities. They also "calculated" the best moment for wars and conquests. They registered their observations in the "Kodizes" (see Writing), but also by inscriptions in temples.