It has perplexed astronomers since being dug up in 1999.

The Nebra Sky Disc is thought to have been made during the Middle Bronze Age in around 1600 BC, and experts believe it could be the first 'sky map' ever created.

The bronze disc, about 32cm in diameter, has a gold inlay clearly representing the moon and/or sun and some stars.

The Sky Disc was discovered in Germany in 1999 as part of a hoard also containing two bronze swords, two small axes, a chisel and fragments of spiral bracelets.

HOW IT WAS FOUND - AND STOLEN The disk's recent history dates to 1999, when two looters using metal detectors discovered the artifact, along with several bronze weapons and tools, in a wooded area near the German town of Nebra, 100 miles southwest of Berlin. Amateur archaeologists Reinhold Stieber and Hildegard Burri-Bayer tried to hawk the disk for $400 000 - and were seized by police officers in the basement bar of a touristy Swiss hotel. After a short trial, the duo, along with the looters, were found guilty of illegally trafficking in cultural artifacts. Advertisement

Experts believe the Sky Disc was a calculator to help Bronze Age people predict the best times for sowing and harvesting in spring and autumn.

It recorded the fact that when the Pleiades, a very obvious group of stars in the night sky which are a familiar sight in the northern hemisphere in winter, were seen next to a new moon, that signaled the beginning of spring, when seeds should be sown, at the latitude of central Germany.

When the star cluster stood next to a full moon, it was a sign that fall had begun and it was harvest time.

The Sky Disc was discovered in Germany in 1999 as part of a hoard also containing two bronze swords, two small axes, a chisel and fragments of spiral bracelets.

A small piece in wood found in one of the swords allowed scientists to date the hoard to around 1600 BC.

The disc was also used to determine if and when a thirteenth month -- the so-called intercalary month -- should be added to a lunar year to keep the lunar calendar in sync with the seasons.

The sophistication of the disk surprised many archaeologists.

'We knew that people back then must have had a certain idea of the seasons and the Moon, as we all have,' Dr. Alfred Reichenberger, a researcher and spokesperson for the State Museum of Prehistory in Halle told Nautilus.

'There are depictions of the cosmos that are older, for example in the chamber tombs of the old pyramids in Egypt.

HOW IT WORKS The Sky Disc was a calculator to help Bronze Age people predict the best times for sowing and harvesting in spring and autumn. The small cluster of stars on the disc has been identified as the Pleiades, a very obvious group of stars in the night sky which are a familiar sight in the northern hemisphere in winter. The disk was developed in four stages: Initially the disk had thirty-two small round gold circles, a large circular plate, and a large crescent-shaped plate attached (left). 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 disk (right). To make space for these arcs, one small circle was moved from the left side toward the center of the disk and two of the circles on the right were covered over, so that thirty remain visible (left). The final addition was another arc at the bottom, the 'sun boat', again made of gold from a different origin. They disappear from view around 10 March and appear again around 17 October, close to the equinoxes which were important times for sowing and harvesting crops. At some point two bands were added to the outside edges. It is thought that the two bands relate to the rising and setting of the sun in midsummer and midwinter, allowing the people to pinpoint the solstices. Advertisement

'But they are schematic…As of today, there has never been something as concrete as the Nebra Sky Disk.'

The Nebra Sky Disc features the oldest concrete depiction of the cosmos worldwide.

In June 2013 the Nebra sky disk was included in the UNESCO's Memory of the World Register calling it 'one of the most important archaeological finds of the 20th century.'

The disk's recent history dates to 1999, when two looters using metal detectors discovered the artifact, along with several bronze weapons and tools, in a wooded area near the German town of Nebra, 100 miles southwest of Berlin.

Amateur archaeologists Reinhold Stieber and Hildegard Burri-Bayer tried to hawk the disk for $400 000 - and were seized by police officers in the basement bar of a touristy Swiss hotel.