The Role of Venus in Mesoamerican Calendrical Origins

In earlier papers I have argued that the unique 260-day sacred almanac which was used
throughout pre-Columbian Mesoamerica traces its origin to the interval between zenithal sun
passages over the Formative site of Izapa in southernmost Mexico. I have argued further that,
by employing the Goodman-Martínez-Thompson correlation, it is possible to date the beginning
of that count very precisely to August 13, -1358 (or 1359 B.C.). (Because the present Gregorian
calendar was not used in the Christian world before A.D. 1582, the equivalent date in the Julian
calendar was August 26, -1358.) As I have also pointed out, each year the southward passage of the
zenithal sun over Izapa is heralded by the Perseid meteor shower on the two preceding evenings, but
on that specific morning in 1359 B C. another astronomical event of significance took place of which
the Zoque priest who formulated the sacred almanac must surely have taken notice. That was the
heliacal rising of the planet Venus (at 2:48 A.M. local time) over Volcán Tajumulco, the highest
mountain in Central America.

We know from the later records of such peoples as the Maya and the Aztecs that the heliacal
rising of Venus was attended with great awe, if not apprehension. Of course we can only speculate
that the priest who set in motion the sacred almanac at Izapa was actually aware that this event would
take place on this auspicious morning, for, if he wasn't, it certainly was a most fortuitous coincidence.

We likewise know that, despite Venus's mysterious "disappearances into the underworld" as it
alternated between being a morning star and an evening star, the Mesoamericans managed to fix the
length of its complete cycle as 584 days. In doing so, they must have also been intrigued to discover
that with the completion of each cycle, the day-number of the sacred almanac decreased by one
whereas the day-name advanced by four.

(See Table 1. Please note that Maya day names are used in the absence of their Zoque equivalents.)


Table 1 -- Heliacal Risings of Venus at Izapa, -1358 to -1342

Julian Date

Maya Date



August 26, -1358

1 Imix


66º 35'

April 1, -1356

13 Chicchan



November 5, -1355

12 Muluc



June 12, -1355

11 Ben



January 17, -1353

10 Caban



August 23, -1350

9 Imix


66º 48'

March 30, -1348

8 Chicchan



November 3, -1347

7 Muluc



June 10, -1345

6 Ben



January 15, -1343

5 Caban



August 21, -1342

4 Imix


66º 43'

(Source: Voyager 1.2 Program, Carina Software, San Leandro, CA 94557.)

From the above table, the calendrical regularity of Venus' heliacal rising is readily apparent,
as is also the fact that with every fifth completion of its cycle Venus once more rises in the vicinity of
the Volcán Tajumulco. Nevertheless, even within the time-span examined in Table 1 it must have
been clear to the priests in Izapa that the heliacal rising of Venus was getting out of phase with the
zenithal passage of the sun, for in the year -1350 the latter did not pass overhead at Izapa until two
days later (on 11 Akbal according to their count), and in -1342 its zenithal passage occurred five days
later (on 8 Chicchan).

As we have seen, assigning a length of 584 days to the cycle of Venus allowed for a very convenient
way to calibrate it calendrically. Although every fifth time its heliacal rise once again took place over
Tajumulco, the interval between it and the zenithal passage of the sun steadily continued to widen.
Had the priest chosen an interval of 584.4 days for the duration of the Venus cycle, the two events
would have remained in phase with one another, but the fact that he did not strongly suggests
that he was unable to conceive of any temporal unit shorter than an entire day -- in other words,
mathematically he was able to think in integers but not in fractions.

On the other hand, it must have been tempting for the priest to have believed that, because of
the calendrical regularity of the Venus count, the real problem of calibrating the two events lay in
defining the interval between the zenithal passages of the sun. In effect, he was recognizing that
although the sun spent 260 days south of Izapa and 105 days north of it, these two values did not
equate to the length of its total cycle -- in other words, to the true length of the solar year. This
problem was far more serious than the growing discrepancy between the heliacal rising of Venus and
the zenithal passage of the sun, for already within four years a lack of calendrical regularity began to
manifest itself. Rather than passing overhead at Izapa on 1 Imix, the sun now passed overhead on
6 Ik instead, and in four more years its passage occurred on 11 Akbal, and so on. Clearly, if the
original intent of his time-count had been to help define the beginning of the rainy season, for
example, then the 260-day sacred almanac was already quickly becoming less and less useful.

To redefine the length of the solar year required a new and hopefully more precise starting point
than the zenithal passage of the sun. Through continued observations of its movements it
gradually became apparent that, as viewed from Soconusco, the sun reached its northernmost
turning point in the sky (i.e., the summer solstice) somewhere behind the great wall of volcanoes
that loomed up on the northeastern horizon. Therefore, by careful planning it should be possible
to find a site where the zenithal passage of the sun on August 13 and the June 22 sunrise over
the highest mountain in Central America could both be calibrated at the same place. As I have
explained in earlier writings, it was this fortuitous combination of circumstances that was
responsible for the choice of Izapa's location.

With the priest now thinking in terms of the summer solstice and the Volcán Tajumulco, it
was perhaps only natural that the earlier correspondence of the heliacal rising of Venus over the
mountain and the zenithal sun passage should once again come to mind. In previous papers I
have demonstrated that the internal structure of the 365-day secular calendar strongly suggests that
it came into use during the period between -1324 and -1321, and that it may in fact have been the
product of the same mind which had developed the sacred almanac just over thirty years earlier.

By employing the Goodman-Martínez-Thompson correlation, we find that the summer solstice
(June 22 in the Gregorian calendar, or July 3 in the Julian calendar) coincided with the date of 0 Pop
during only those four years. It is also interesting that there were heliacal risings of Venus in two of
those years -- one at 4:12 A.M. in -1324 when the planet rose at an azimuth of 67º 35', or nearly
over Tajumulco, and one at 3:10 A,M. in -1321 when its rise took place at an azimuth of 72º. The
date of the first occurrence according to the sacred almanac was 4 Manik and of the second, 7 Ik.
One is tempted to conclude, therefore, that of the two possible dates for the secular calendar's
beginning it was the former on which it was set in motion. Indeed, it may have been that the choice
of 4 Manik for the initiation of the 365-day secular count gave rise to the notion held by later peoples,
such as the Aztecs, that previous creations of the world likewise occurred on days numbered 4 and
that our present world shall also end on a day numbered 4.

(It may be of interest to note that the next heliacal rising of Venus on August 13th will take
place in the year 2001 at 3:15 A.M. On that occasion, its azimuth will be 67º 21', or still very close
to Volcán Tajumulco. In the year 2003 a heliacal rising of Venus will occur on the summer solstice
(June 22) at 4:37 A.M. closer yet to Volcán Tajumulco, namely at an azimuth of 67º 02'.)

(Note that references for this and the other papers are found on the 'home page' of this article.)

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