Glyph X of the Maya Lunar Series: An Eighteen-Month Lunar Synodic Calendar

The astronomy of the ancient Maya is an impressive achievement. Without the use of optical instruments, the Maya of the Classic period observed and recorded recurrent eclipse periods as well as the synodic orbit of Venus. Early work on the Maya hieroglyphs interpreted the chronological and calendric systems of the Classic period inscriptions and demonstrated the existence of a lunar synodic calendar. Many of the Lunar Series hieroglyphs that record the lunar synodic calendar have been interpreted, but the meaning of Glyph X has remained unknown. This report offers the explanation that Glyph X records positions in an eighteen-month lunar calendar. The Classic period Maya may have used this eighteen-month calendar to establish an average length for the lunar synodic month.