Proceedings of the International Astronomical Union

Contributed Papers

Measuring deep time: the Sidereal Year and the Tropical Year in Maya inscriptions

Michael J. Grofea1

a1 Department of Anthropology, American River College, 4700 College Oak Drive, Sacramento, CA 95841, USA email: [email protected]


Maya inscriptions contain numerous examples of long intervals of time that count both backward and forward from a fixed point of historical reference to specific mythological dates, often thousands of years in the past or future. This paper considers the evidence that these intervals incorporated precise calculations of both the sidereal year and the tropical year. Furthermore, it outlines a specific methodology for assessing the likelihood that these distance numbers were either intentionally calculated to incorporate these astronomical measurements, or if these results are merely coincidental.

(Online publication July 26 2011)


  • Maya inscriptions;
  • sidereal year;
  • tropical year