The Mayan (long Count) calendar is based on astronomical observations.
Mayan Calendar -- from Eric Weisstein's World of Astronomy
" A complicated and accurate calendar using three simultaneous independent systems. It consisted of the Long Count, Tzolkin, and Haab. The Long Count is related to precession of the equinoxes, and will end in 2012 when the winter solstice will be very near the point at which the ecliptic plane and galactic plane intercept "
I have read books by John Calleman and watched videos by John Jenkins - they disagree about the long count 'end date'.
What is meant by 'end' is also just speculation