Season of the Pleiades

In the equatorial constellation of Taurus, beyond the bright red star Aldebaran, can be seen what at first sight might be taken to be no more than a faint mist.

This patch is a cluster of stars so youthful in astronomical terms that some are still surrounded by the nebula of their creation: the Pleiades. They are so far from Earth that only the minutest fraction of their number are actually visible to the naked eye: Atlas (father) and Pleione (mother) and their seven daughters, Alcyone, Maia, Electra, Taygeta, Merope, Asterope and Celaeno, arguably the most important stars of the ancient world.

Chaldean astronomers certainly thought so. They called the cluster Chimah, meaning a revolving pivot moving other bodies with it. This idea was given credence by 19th century, astronomers who believed Alcyone, the brightest of the stars, to be the centre of gravity of the Solar system around which Sun and planets moved through space.

Discredited as it was later of course, this was no worse for all that than the idea of the ancient Greeks that the sky was a concave mirror reflecting idealised impressions of humanity. In Hesiod's day c800 BC, Greek farmers reaped their corn when the Pleiades rose at Sunrise in May, and ploughed their fields when they set at Sunrise in November.

Seven Sisters they called them, from the seven daughters of Atlas and Pleione who died of grief and were placed as stars in the heavens, unaccountably echoing the Seven Gods of the Sumerians, Seven Hathors of the Egyptians, Company of Maidens of the Florida Indians and Karatgioruk (Young Women) of the Australian Aborigines. Vergilae from ver, the spring, came later. The modern name is derived from pleein, to sail, in recognition of the calm seas heralded by the Pleiades' appearance.

It is little wonder then, considering their importance, that the Hecatompedon in Athens had been oriented to the Pleiades when, built around 1500 BC, or the Merrivale Avenue near Walkhampton in Devon similarly some 500 years later. This latter is so nearly parallel with the Cursus at Stonehenge that the idea has been mooted that each enjoyed a similar significance relating to the heliacal rising of the Pleiades at the beginning of the Beltane Fire Festival.

Appropriate really if it should be go; fire and Sun being inseparable in the Celtic mind and a heliacal rising referring to a star, or in this case a cluster of stars, making a first appearance in the dawn sky immediately prior to the Sunrise itself. The importance of this found an echo in some religious rites of ancient Mesoamerica.

Other rites also depend on the Pleiades. The Sherente of Brazil still reckon their years to begin when the Pleiades appear as the Sun makes its June exit from the constellation of Taurus. The Navajo associate the stars with Black God, creator of fire and light, a recognisable form of the group appearing on the face of any depiction of the deity.

The Maya called the cluster Tzab, the rattle (of the rattlesnake). In the Aztec Florentine Codex of Central Mexico the group, identified as Tianquiztli, the Market Place, ensured the survival of civilisation for a further 52-year cycle by transiting the zenith at midnight during the ceremony of The Binding of the Years.

Yet it was with an entirely different culture, a millenium earlier, that perhaps the greatest ever recognition of the Pleiades is to be found. Teotihuacan, largest and most influential of all the cities of ancient Mesoamerica, is the earliest example of what has become known as the `17° family of orientations' in reference to the angle at which their principal axes run East of due North.

Built around the beginning of the Christian era on a grid which, since the course of a nearby river was altered to suit the pattern, cannot be claimed to simply conform to local topography, the city possesses a major axis, defined by the Street of the Dead, skewed 15° to the East of North. This is the same direction in which at least three other main thoroughfares are known to have run and at right angles to a baseline lying within 1° of the line of setting of the Pleiades.

Although a singular enough reason for the angle of layout of any city, this was not the prime mover in this instance as investigation revealed. On the day of the first of the seasonal demarcations brought into being

by the two annual passages of the Sun across the zenith, the Pleiades underwent heliacal rising. They announced by their appearance the beginning of that most important of all days when the Sun at high noon cast no shadows.

Linked to the cult of the Diving Sun God, an inverted figure common to the friezes decorating so much which was sacred in Mesoamerica, this was an event of incredible significance. The descent of the god, drawing the noon shadows down with him, was invariably followed by rains caused by the heat of the vertical Solar rays. His death therefore promised life to his believers as deaths of gods throughout the world have done since time immemorial.

Ceremonial centres in the vicinity of Teotihuacan built over a period of 1500 years reflect the sacred orientation. So too do the more distant cities of Tenayuca, Tepozteco and Tula, as well as buildings at Chichon Itza over 900 miles away. The latter especially are an act of very great faith, considering the alien nature of the environment.

Whether anyone involved in the work had taken into account the movement of the Earth's pole of rotation among the stars before transforming belief into action is debatable.

However, by the time these copy-cat cities were springing up the Pleiades no longer set along the Teotihuacan East-West axis. Nor by the end of the 9th century did they continue to announce the zenith passage of the Sun.

The great civilisation of Mexico was declining, and though the priest rulers of the day still planned their centres of worship with an eye to the orientation of the holy city, it is doubtful that they retained the knowledge of the original purpose by which their predecessors had been inspired.

To paraphrase a passage from one of the tragedies by the Greek writer Euripedes, 'The Pleiades were passing.' Their light would never shine so bright again.