Nebra sky disk

The Nebra sky disc (german: Himmelsscheibe von Nebra) is a bronze disc of around diameter and a weight of , having a blue-green patina and inlaid with gold symbols. These symbols are interpreted generally as the Sun or full moon, a lunar crescent, and stars (including a cluster of seven stars interpreted as the Pleiades). Two golden arcs along the sides, interpreted to mark the angle between the solstices, were added later. A final addition was another arc at the bottom with internal parallel lines, which is usually interpreted as a solar boat with numerous oars, though some authors have also suggested that it may represent a rainbow, or the Aurora Borealis.

The disc was found buried on the Mittelberg hill near Nebra in Germany. It is dated by archaeologists to and attributed to the Early Bronze Age Unetice culture. Various scientific analyses of the disc, the items found with the disc, and the find spot have confirmed the Early Bronze Age dating.

The Nebra sky disc features the oldest concrete depiction of astronomical phenomena known from anywhere in the world. In June 2013, it was included in the UNESCO Memory of the World Register and termed "one of the most important archaeological finds of the twentieth century."

Discovery

The disc, together with two bronze swords, two hatchets, a chisel, and fragments of spiral bracelets were discovered in 1999 by Henry Westphal and Mario Renner while they were treasure-hunting with a metal detector. The detectorists were operating without a license, and knew their activity constituted looting and was illegal. Archaeological artefacts are the property of the state in Saxony-Anhalt. They damaged the disc with their spade and destroyed parts of the site. The next day, Westphal and Renner sold the entire hoard for 31,000  DM to a dealer in Cologne. The hoard changed hands, probably several times, within Germany during the next two years, being sold for up to a million DM. By 2001 knowledge of its existence had become public. In February 2002 the state archaeologist, Harald Meller, acquired the disc in a police-led sting operation in Basel from a couple who had put it on the black market for 700,000 DM. The original finders were eventually traced. In a plea bargain, they led police and archaeologists to the discovery site. Archaeologists opened a dig at the site and uncovered evidence that supported the looters' claims. There were traces of bronze artefacts in the ground, and the soil at the site matched soil samples found clinging to the artefacts. The disc and its accompanying finds are held by the State Museum of Prehistory in Halle, Saxony-Anhalt, Germany.

The two looters received sentences of four months and ten months, respectively, from a Naumburg court in September 2003. They appealed, but the Appeals Court raised their sentences to six and twelve months, respectively.

The discovery site is a prehistoric enclosure encircling the top of a elevation in the Ziegelroda Forest, known as ''Mittelberg'' ("central hill"), some 60 km west of Leipzig. The surrounding area is known to have been settled in the Neolithic era, and Ziegelroda Forest contains approximately 1,000 barrows.

At the enclosure's location, the sun seems to set every summer solstice behind the Brocken, the highest peak of the Harz mountains, some 80 km to the north-west. The treasure-hunters claimed the artefacts were discovered within a pit inside the bank-and-ditch enclosure.

Dating

Axes and swords found buried with the disc can be dated typologically to c.1700-1500 BCE. Remains of birch bark found in the sword hilts have been Radiocarbon dated to between 1600 and 1560 BCE, confirming this estimate. This corresponds to the date of burial, at which time the disc had likely been in existence for several generations. Analyses of metal radioactivity and the corrosion layer on the disc further support the early Bronze Age dating.

Origin of the metals

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, whilst the gold was thought to be from the Carpathian Mountains. A more recent analysis found that the gold used in the first development phase (see below) was from the River Carnon in Cornwall, United Kingdom. The tin present in the bronze was also of Cornish origin.

History

As preserved, the disc was developed in four stages:
# Initially the disc had thirty-two small round gold circles, a large circular plate, and a large crescent-shaped plate attached. The circular plate is interpreted as either the Sun or the full Moon, the crescent shape as the crescent Moon (or either the Sun or the Moon undergoing eclipse), and the dots as stars, with the cluster of seven dots likely representing the Pleiades.
# At some later date, two arcs (constructed from gold of a different origin, as shown by its chemical impurities) were added at opposite edges of the disc. To make space for these arcs, one small circle was moved from the left side toward the centre of the disc and two of the circles on the right were covered over, so that thirty remain visible. 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). Given that the arcs relate to solar phenomena, it is likely the circular plate represents the Sun not the Moon.
# The final addition was another arc at the bottom, identified as " sun boat", again made of gold, but originating from a different source.
# By the time the disc was buried it also had thirty-nine holes punched out around its perimeter, each approximately 3 mm in diameter.

Image:Nebra-1.jpg, 1) On the left the Full Moon, on the right the Waxing Moon, and between and above, the Pleiades
Image:Nebra-2.jpg, 2) Arcs were added on the horizon for the zones of the rising and setting Sun; individual stars were shifted and/or covered
Image:Nebra-3.jpg, 3) Addition of the rainbow or " sun boat".
Image:Nebra-4.jpg, 4) Diagram of the disc in its current condition (a star and a part of the Sun—or Full Moon—have been restored)

Significance

The find is regarded as reconfirming 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 the summer and winter solstices. While much older earthworks and megalithic astronomical complexes, such as the Goseck circle and Stonehenge, had already been used to mark the solstices, the disc presents this knowledge in the form of a portable object. The disc may have had both a practical astronomical purpose as well as a religious significance.

The depiction of the Pleiades on the disc in conjunction with a crescent moon has been interpreted as representing a calendar rule for harmonising the solar and lunar calendars. This rule is known from a Babylonian text dating from the 7th century BC (MUL.APIN). According to this rule, a leap month should be added when the Pleiades appear next to a crescent moon a few days old in the spring, as depicted on the disc. This conjunction occurs approximately every three years. Harald Meller suggests that knowledge of this rule may have come from Babylonia to Central Europe through long distance trade and contacts, despite it being attested earlier on the Nebra disc than in Babylonia.

Archaeoastronomist Emília Pásztor has argued against a practical astronomical function for the disc. According to Pásztor "the close agreement of the length of the peripheral arcs with the movement of the sun’s risings or settings might be a pure coincidence". This claim is undermined by the finding of a similar feature on the roughly contemporary gold lozenge from Bush Barrow at Stonehenge, where the acute angles of the overall design (81°) are equal to the angle between the solstices at the latitude of Stonehenge. According to Euan MacKie (2009) "The Nebra disc and the Bush Barrow lozenge both seem to be designed to reflect the annual solar cycle at about latitude 51° north." MacKie further suggests that both the Nebra disc and Bush Barrow lozenge may be linked to the solar calendar reconstructed by Alexander Thom from his analysis of standing stone alignments in Britain. Both the Nebra sky disc and Bush Barrow gold artefacts were made with gold from Cornwall, providing a direct link between them. According to Sabine Gerloff the gold plating technique used on the Nebra sky disc also originated in Britain, and was introduced from there to the continent.

Authenticity

There were some initial suspicions that the disc might be an archaeological forgery. Peter Schauer of the University of Regensburg, Germany, argued in 2005 that the Nebra disc was a fake and that he could prove that the patina of the disc could have been created with urine, hydrochloric acid, and a blow torch within a short amount of time. He had to admit in court that he had never held the disc in his own hands, unlike the eighteen scientists who had examined the disc. Scientific analyses of the patina (or corrosion layer) have confirmed its authenticity.

Richard Harrison, professor of European prehistory at the University of Bristol, stated in a BBC
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