The Nebra Sky Disc

The disc is a sheet of low-tin bronze, thicker at the centre (4.6 mm) than the rim (1.5 to 1.8 mm), with gold foil set into grooves. Its alloy is copper with 2.6% tin and small amounts of nickel, arsenic and zinc⁠[3]. The image was changed over time: horizon arcs were added on the rim, then the curved band often read as a boat, and finally a ring of holes was punched around the edge; one arc is now missing. The excavators count five phases⁠[3]⁠[2].

Corrosion is uneven, with pitting on one half only, which the analysts read as the disc having stood upright in the ground. The rim carries fresh damage from the looters' pickaxe⁠[2]. The disc and hoard are in the Landesmuseum für Vorgeschichte in Halle, which publishes a 3D model of the objects⁠[7].

The find story rests on a criminal case. The looters were convicted, then testified against the two dealers who last held the hoard. The Regional Court of Halle concluded in 2005, with what it called a probability close to certainty, that the disc was found with the hoard on the Mittelberg; the Higher Regional Court in Naumburg upheld the verdict⁠[2].

The State Office excavated the spot the looters showed in 2002. It found their pit, the shards of a West German mineral-water bottle they said they had smashed there, marks of their fire-brigade pickaxe in the section, and an enrichment of copper (up to 138 µg/g) and gold (19 ng/g) in the undisturbed soil under the pit, consistent with metal corroding there for a long time⁠[2].

The copper's trace elements and lead isotope ratios match the Mitterberg ores, which were mined mainly in the Bronze Age. The gold's trace elements match natural gold from the Carnon River in Cornwall, and the disc's tin isotope ratio fits Cornish tin ores⁠[2]⁠[4]⁠[5].

Authenticity. An early allegation that the disc was a modern fake was answered by the analyses of patina, metal, isotopes and lead-210, and is not repeated by the 2020 critics⁠[2].

Association with the hoard. A forensic soil analyst compared soil adhering to the disc and to one sword with a sample taken at 30 to 40 cm depth at the findspot and with soils from geologically similar places. The disc and sword samples matched the Mittelberg sample almost completely; a third sample on an axe matched less well. The authors call the common origin highly probable but note that one reference sample cannot give certainty⁠[2].

Manufacture. A 2024 study sectioned a sample from the rim and forged a replica of the same alloy. The disc has medium grains with annealing twins and elongated sulphide inclusions; it cannot have been cast to shape. It was cast as a thick preform and forged in about ten cycles of heating to nearly 700 °C and hammering, then heat treated⁠[3].

Lead isotopes. Measurements in Freiberg (2003) and Mannheim (2007) of the disc, swords and chisel are published in a table; the disc's ratios vary between drill holes, which the analysts attribute to the variable lead of the Mitterberg ores and to mixed metal⁠[2].

The calendar reading holds that the disc is an image of the night sky. The seven-star group is the Pleiades, and the horizon arcs relate to the summer solstice; from the Mittelberg the sun sets behind the Brocken on 21 June. The image is read as a memory aid and leap rule for reconciling the lunar and solar years⁠[2]. Meller and Kai Michel argue that this knowledge came from Mesopotamia⁠[8].

The symbolic reading accepts that the disc shows sun or moon and stars but denies that it maps a real sky or encodes a calendar; Pásztor and Roslund read it as the cosmological device of a local warrior society⁠[1].

The sky-event reading treats the seven stars as a planetary conjunction with Castor and Pollux in 2210 BC and the large disc as a supernova⁠[9]. It has not been taken up by archaeologists.

The Iron Age reading holds that the disc was not found with the hoard, possibly not on the Mittelberg, and that its style fits the first millennium BC better than the Bronze Age⁠[6]. The challenge drew some 70 press reports in 2020 and an immediate statement from the State Office⁠[10]. The analysts answer that the court, the excavation of the looters' pit, the soil chemistry and soil matching, the metal and isotope data and the boat motif all point to the Early Bronze Age, and that a text of the La Tène period, Aratus, says only six Pleiades could be seen⁠[2].

No method dates a copper alloy directly, so the date will continue to rest on the association with the hoard. A larger set of reference soils from the Mittelberg and the region, analysed blind against the adhesions on all hoard objects, would turn the soil match from highly probable into a measured likelihood ratio.

The calendar reading would be tested by a pre-registered analysis of the star positions against random placements, with the arcs measured on the 3D model rather than photographs. The forthcoming full physical atlas of the disc announced by the State Office would give the data needed to do this⁠[3].