139
DIETER DOTTING and MATTHIAS SCHRAMM
The Sidereal Period of the Moon
in Maya Calendrical Astronomy*
»The prime use of Maya astronomy was to learn the habits of the
celestial powers so as to make predictable the hazards of living under
their influence.«
Floyd G. Lounsbury (1978: 804)
* We dedicate this paper to Prof. Thomas S. Barthel (Tübingen) on the occasion of his 65th
birthday.
Abstract
1. Historical dates of the Maya are sometimes separated by multiples of astronomical periods.
So we find the triple sidereal period of the moon, approximated by 82 d , but also improved
values. In Palenque the dates of Lord Pacal’s birth and accession are separated by full triples
of sidereal months. This distance is mirrored by a similar number of triples between birth and
inauguration of PacaPs mythical ancestress in the distant past. The initial dates of El Peru
Stela 34 (separated by 82 d ) are linked with Pacal’s dates and with the Katun ending 9.12.0.0.0
again by full triples of sidereal months. These and many more examples suggest that the
encountered multiples of lunar periods are not the result of mere chance.
2. By a theoretical evaluation the sidereal month is put into the wider context of Maya
astronomy. Holding the place of rudimentary angular calculations, the mean sidereal motion
of the moon can serve to give a common frame to the celestial phenomena of day and night, to
the course of the sun with respect to that of the stars. This frame is considered a first step to a
coordinate astronomy. The almanac of Codex Paris, pp. 23/24, is demonstrated to fulfil similar
purposes and to give a scheme for the typical relations applying to the motions of the sun and
the moon.
Distances revealing multiples of lunar and solar periods between Long Count dates
of the Mayan hieroglyphic inscriptions have never been the subject of systematic
research. Barthel (1951) screened a number of dates from Piedras Negras, Yax-
chilan and Naranjo for lunar period distances, at a time when the historical impact
of these dates was not yet known. He found some of the dates to be linked by a full
multiple of lunations/lunar synodic months (29 d .53059) and/or lunar sidereal months
(27 d .32166). Every 27/3 days, the moon completes the cycle of the ecliptic, passes
the same group of stars, but only every 82 d = 3x27/ days (precisely 81 d .96498) it
passes the same background of stars also in the same time of the night. Occasionally
Barthel encountered dates that were separated by full multiples of lunations or
sidereal months from the nearest Katun or half-Katun ending, which implies the
same moon age or the same station of the moon in the ecliptic at the corresponding
dates. One of the more exciting findings was (p. 229) the distance of 3606 d = 132
sidereal months = 44 triple sidereal months (modern value 3606“.46) between the
dates of Yaxchilan Stela 12, (9.15.10.17.14) 6 lx 12 Yaxkin, later known to be the
death date of Lord Shield-Jaguar, and (9.16.1.0.0) 11 Ahau 8 Zee, later showm to be
the accession date of his son Bird-Jaguar. On the corresponding Julian dates in the
well established 584,285 correlation, 742-Jun-15 (moon age 8 d ) and 752-Apr-29
(moon age 12 d ), the waxing Moon passed the bright star Spica/a Virginis at the
eastern border of Virgo at about the same time of the night (Dutting 1985: 269).