Science News

Nebra sky disk discarded because of volcanic ash, scientists say

By Thomas Schoene Aug 23, 2010, 15:49 GMT

Halle/Mainz, Germany - A catastrophic volcanic eruption spewing huge clouds of ash about 3,600 years ago was behind the burial of the Nebra sky disk, one of the most spectacular archaeological finds in recent years, according to scientists at Mainz and Halle-Wittenberg universities in Germany.

The 3,600-year-old disk, discovered in 1999 near the town of Nebra in the eastern German state of Saxony-Anhalt, is the oldest known representation of the night sky. It is thought by some to have been used as an astronomical clock to determine when to add a thirteenth month synchronising the lunar calendar with the solar year.

The disk would be held against the sky, and when the position of the celestial objects matched those on the disk, the intercalary month would be added. Scientists said the disk became worthless after the eruption on the Mediterranean island of Thera - north of Crete and also known as Santorini - which ejected ash that obscured the sky all the way to Central Europe for 20 to 25 years.

Average temperatures dropped one or two degrees during this time.

'There were cool, wet summers with devastating crop failures and exceptionally cold winters,' said Francois Bertemes, a professor at Halle-Wittenberg University's Institute of European Art History and Archaeology.

The changes were inexplicable to people of the Bronze Age, who were followers of a sun cult. Their faith in the gods was shaken, Bertemes remarked, and 'they called the priests and (the priests') rituals into question.'

Scientists said the 32-centimetre-diameter bronze disk, with gold-leaf appliques representing the sun, moon and stars, was desecrated as a cult object and buried as an offering to the gods - along with two swords decorated with gold, Bronze Age spiral bracelets and bronze axes - on then sacred Mittelberg hill.

'The natural occurrences were almost certainly very bewildering to prehistoric people in Central Europe,' said Frank Sirocko, a sedimentologist at Mainz University's Geosciences Institute.

Sirocko and a team of researchers have analyzed the effects of weather and climate on human development for years. He has also looked into the Thera eruption.

'It was surely a watershed in the Bronze Age and it's no coincidence that use of the stone circles at Stonehenge ceased 3,600 years ago, and that the Nebra sky disk was buried,' Sirocko said.

'Maybe the act was meant to make the gods merciful and get them to restore the previous conditions,' said Bertemes, referring to the disk's burial.

The Nebra sky disk has been on permanent display at the State Museum of Prehistory in Halle since 2008. Nebra Ark, a multimedia visitors' centre with information on the disk and its history, is located near the site where the disk was discovered.