The Secrets of the Nebra Sky Disc
The Nebra Sky Disc is a 3,600-year-old bronze disc which, according to UNESCO, features "the oldest concrete depiction of cosmic phenomena worldwide." The disc is such an extraordinary piece that it was initially believed to be an archaeological forgery. However, detailed scientific analysis revealed that it is indeed authentic and the precious artefact is now included in UNESCO’s ‘ Memory of the World ’ register, an international initiative launched to safeguard the documentary heritage of humanity, and is being held in the State Museum of Prehistory in Halle.
The Nebra Sky Disc was discovered in 1999 by two amateur treasure hunters illegally using a metal detector in Ziegelroda Forest, Saxony-Anhalt, Germany. It had been ritually buried in a prehistoric enclosure atop a hill (the Mittelberg), along with two precious swords, two axes, two spiral arm-rings and one bronze chisel. The enclosure is oriented in such a way that the sun seems to set every solstice behind the Brocken, the highest peak of the Harz Mountains, some 80 km to the north-west. The surrounding area is known to have been settled since the Neolithic, and Ziegelroda Forest is said to contain around 1,000 barrows.
The swords found with the disc. Photo source: Wikipedia
The scientific studies of the Nebra hoard are probably among the most thorough ever carried out on any archaeological find in Europe. Study began when the objects were first impounded in 2002 and continued until the end of 2007. Nevertheless, dating the artifact has posed many difficulties, and while scientists have been able to determine that it was buried in 1,600 BC, they are unable to determine its date of manufacture, meaning it could be much older than its burial date.
The Nebra bronze sky disc measures approximately 30 cm in diameter, weighs 2.2 kg, and is decorated with a blue-green patina and inlaid with gold symbols. These are interpreted generally as a sun or full moon, a lunar crescent, and stars (including a cluster interpreted as the Pleiades).
Two golden arcs along the sides were added later (one has since become lost). These were constructed from gold of a different origin, as shown by its chemical impurities. The two arcs span an angle of 82°, correctly indicating the angle between the positions of sunset at summer and winter solstice at the latitude of the Mittelberg (51°N).
Mittelberg hill, where the Nebra Sky Disc was found. Photo credit: LDA Sachsen-Anhalt
A final addition was another arc at the bottom surrounded with multiple strokes of uncertain meaning, variously interpreted as a Solar Barge (“the sun boat”) with numerous oars, or as the Milky Way. By the time the disc was buried it also had thirty-nine or forty holes punched out around its perimeter, each approximately 3 mm in diameter. According to state archaeologist Harald Meller, it is likely the circular plate represents the Sun not the Moon, given that the arcs relate to solar phenomena.
The stages in the life of the Sky Disc. Photo credit: LDA Sachsen-Anhalt
According to an initial analysis of trace elements by x-ray fluorescence by E. Pernicka, then at the University of Freiberg, the copper originated at Bischofshofen in Austria, while the gold was thought to be from the Carpathian Mountains. However, a more recent analysis found that the gold used in the first phase was from the river Carnon in Cornwall. The tin content of the bronze was also from Cornwall.
The Nebra Sky Disc reconfirms that the astronomical knowledge and abilities of the people of the European Bronze Age included close observation of the yearly course of the Sun, and the angle between its rising and setting points at summer and winter solstice. While much older earthworks and megalithic astronomical complexes such as the Goseck circle or Stonehenge had already been used to mark the solstices, the disc is the oldest known "portable instrument" to allow such measurements.
Astronomer Ralph Hansen maintains that the disc was an attempt to co-ordinate the solar and lunar calendars to tell Bronze Age Man when to plant seeds and when to make trades, giving him an almost modern sense of time. "For everyday calendrical purposes, you would use Moon years. But for designing when to plough fields and when to harvest, you use Sun years," said Hansen.
However, not everyone agrees that the Nebra Sky Disc was used for measuring astronomical phenomena. "It's a difficult question to answer, but I do not think it was used as an instrument used for observing objects in the sky," said Curt Roslund, an astronomer at Gothenburg. Instead, Roslund argues that few features on the disc tend towards exact representation and that it is more likely to have been of symbolic value - perhaps used in shamanic rituals.