Astronomy was very important to Mayas. They
constructed special buildings for observing stars,
such as Caracol at Chichen Itza and Group E at
From these they noted the appearance and
disappearance of celestial bodies in different
seasons. They recorded annual cycle of the sun as
365 days and also the lunar cycle with only small
margin of error.
They drew up tables for solar eclipses that would
occur in a period of 33 years, calculating cycles
of Mars, Jupiter and Saturn. They also plotted the
movement of certain constellations such as
Pleiades, which they called Tzab (serpent's
rattle) and Gemini or Ac (turtle).
They used this knowledge to create two calendars.
One was the solar, called Haab, with 365
days, divided into 18 months of 20 days, each plus
5 extra ones named Uayeb. The other was the
ritual calendar or Tzolkin of 260 days,
designated by 20 signs and 13 numbers, which was
used to determine festivals of gods and predict
Generally the two were combined, and Mayas
recorded the same date in both Tzolkin and Haab.
To fix a date in certain year, there was new
combination, and 18980 days would have to go by
before the combination was repeated, i.e. 52 solar
years and 73 ritual years. Mayanists have named
this calendar "Calendar Round".