The heavens have always fascinated humanity, and evidence of quite sophisticated understanding of the movements of stars and planets, including the alignment of sacred sites with particular heavenly bodies or astronomical events, and dating back millenia, have been found on every inhabited continent.

Of course, such observations and analyses were not undertaken for anything remotely like modern science, but for religious and ritual purposes, and determining the change of seasons. These activities were often centred on 'complexes' or monuments of wood or stone, of varying degrees of sophistication, which were probably both 'temples' and 'observatories'. The classic, and unusually complex, example is Stonehenge in England, constructed in three phases between 3000 BC and 1500 BC, the main axis of which is aligned with the midsummer sunrise, and an observer in the centre of the complex can determine both when summer is at it height and winter is at its deepest.

Simpler equivalents to Stonehenge have been found all over the world – so, are there any in South Africa? We don't yet know.

Oddly, hardly any work has been done on this field, known as archaeo-astronomy, in Southern Africa.

A local pioneer in this discipline is Richard Wade who has established the Nkwe Ridge Observatory to the east of Pretoria, and he has so far focused his researches on Great Zimbabwe, although, as he points out, there was a cultural unity linking what is now the Republic of Zimbabwe with the Limpopo, Gauteng, Mpumalanga and perhaps even Free State provinces of South Africa.

Before the advent of modern light and air pollution, the night skies over the South African highveld gave, particularly in winter, a superbly clear view of the stars and planets, and this brilliant display must surely have impressed the indigenous African peoples who saw it nearly every night.

Concerning Great Zimbabwe, Wade points out that a number of small monoliths are embedded in the top of the eastern arc – that is, facing sunrise, moonrise and star rise – of the main enclosing wall, but none are found on the rest of circumference.

Furthermore, standing atop the platform found at the eastern end of the Great Enclosure, as it is called, one can see over the wall to the horizon.

To someone standing on that platform, three of the monoliths clearly align with the three stars of the constellation Orion, namely Saiph, Alnilam and Bellatrix, when they rise heliacally (that is, just before sunrise) on the winter solstice (that is, the shortest day of the year). The central of these three monoliths also marks the central belt star of Orion, the start and end point of the Venus synodic period, as well as the equinoxes.

(The equinoxes are those two days each year when day and night are of equal length; the vernal equinox occurs on September 23 in the Southern Hemisphere, and so can be regarded as marking the end of winter, or the dry season, and the arrival of summer, or the rainy season, while the autumnal equinox occurs on March 20.

The Venus synodic period lasts 583,9 days, divided into four phases – appearance, which lasts 263 days, disappearance, 50 days, apearance, 260 days, and disappearance, 8 days.) Furthermore, the tip of the small conical tower found within the Great Enclosure of Great Zimbabwe, when viewed from the platform, also aligns with the vernal equinox sun at sunrise.

In fact, Wade has determined that there are 35 alignments of heavenly bodies with the perimeter wall monoliths when viewed from the platform, and he suggests that the platform originally had emplaced, at its centre, a single monolith that could have been two metres high, providing more precise alignments.

Most striking, however, is Wade's discovery that the large conical tower in Great Zimbabwe, which dates from the 14th century, is, when seen from the platform, in alignment with the supernova remnant RX J0852.0-4622 in the constellation Vela. The point is that RX J0852.0-4622 is now believed to have gone supernova some time between AD 1300 and 1340, and would have been clearly visible in the Southern Hemisphere. There is thus a most suggestive correlation between the construction of the large tower and what would have been a spectacular event in the heavens.

Clearly, archaeo-astronomy is a discipline in its infancy in South Africa, but what is already obvious is that, when South Africans look upwards to study the night sky, they are following in a tradition that runs deep into the country's and region's past.

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