Turn, and Turn Again

The constellations flow.

And the axis of the world beneath inscribes a circle in the sky a thousand

generations round, bestowing briefly as it passes by the honour of The

Pole on certain favoured stars.

Fragments of Berossus, Vega

Though the ancients conceived of the celestial sphere as eternal, unchangeable and perfect — and so were greatly disturbed by the appearances of "new stars" (novas and supernovas) and other "meteorological" phenomena (so called because they were "lofty" or "atmospheric") such as comets — that the heavens are not immutable is now common knowledge.

The so-called fixed stars move with respect to the solar system as they and we orbit the centre of the galaxy at different distances and varied speeds, and wander through space with our own peculiar, local motions; but such proper motions are not discernible by the human eye in the course of a single lifetime. What we may notice however is the precession of the equinoxes — the slow circling of the pole.

The precession of the equinoxes is the visible effect of the rotation of the Earth's axis — not the rotation of the Earth about its axis but the slow movement of the axis itself, as shown below. The cause is gyroscopic precession caused primarily by the moon's gravitational pull on a somewhat-less-than truly spherical Earth, but since there are other forces acting on the Earth (such as the Sun's gravity) and the Earth itself is not completely rigid, the motion of the pole illustrated above is neither a perfect circle nor perfectly periodic (every time a major earthquake redistributes the Earth's mass, the pole shifts by a microscopic but measurable amount).

The Aztec and the New Fire Ceremony

Codex Laud, folio VIII at FAMSI

Time is spiralled, time is spun; time weaves tendrils through the days.

Tonight we mourn the dying sun; tonight my heart will feed the flames.

Fragments of Berossus, Alcor
 

In the pre-Columbian era, before the Spanish conquest, a variety of calendrical systems were in simultaneous use by the cultures of Mesoamerica, including both the Maya and the Aztec.

For the Aztec, two systems, the 260-day cycle (tonalpohualli) and the 365-day cycle (xiuhpohualli), were particularly important. The 260-day cycle comprised thirteen repetitions of twenty day names, and the 365-day period consisted of eighteen such "veintenas" (the Spanish name; the original Nahuatl is no longer known) plus five nemontemi, or nameless days.

Because of the disparate lengths of the two cycles, the combination of tonalpohualli and xiuhpohualli dates formed an even longer cycle of approximately 52 solar years (365.25 days). After 18,980 days (the smallest number divisible by both 260 and 365; 18,980 = 73 x 260 and 52 x 365) the calendar combinations would then repeat* if the world did not end first — which could only be prevented by human sacrifice.

Quipu

In the Betelgeuse star-myth an aged storyteller reads from a quipu. Quipu were Inca record keeping devices consisting of knotted, coloured strings; they were known to be used for recording numerical information but, since they were also used in communicating histories, may also have contained text. Unfortunately, we no longer know how to read them, and the few quipu that survived deliberate suppression and destruction by the Spanish remain largely undeciphered — though scholars such as Gary Urton have made some progress in recent years. (Click Read more for a larger image)