I don't think there is a problem with asking a lot of questions on Enotes, and I choose to give people the benefit of the doubt in terms of motives. As for answering the question, the heavens played a very prominent role in Mayan cosmology, as it did with many ancient peoples. Much of this had to do with the fact that farmers knew when to plant crops and based on the position of stars in the sky. So intense study of the skies was crucial, and eventually took on religious significance. Because it was so important to their worldview, they invested a great deal of time and energy in studying the skies, and were highly scrupulous in recording what they saw. 

They spent all their time watching the heavens.  Sure, they didn't have telescopes and such, but the sorts of observations they were making didn't need those.  All they needed was a lot of attention to detail and a lot dedication.  They had those things and so they came to know a great deal.