The Chinese star chart is the earliest known manuscript atlas of the night sky.
It was produced in central China around 700 and it shows over 1,300 stars visible to the naked eye – centuries before the telescope was invented.
The different colours – black, red and white – indicate those stars observed by three Chinese astronomers from ancient times, over 1,000 years before. They are accurately plotted using a projection system to depict the curved sky on a flat piece of paper (invented by the Chinese before the 1st century BC).
The projection is very similar to that developed by the 16th-century Flemish cartographer Gerardus Mercator and still used in many maps today. The night sky is divided into 12 segments, and the final chart shows the north polar region, looking straight up.
In China, the movement of the stars in the sky was thought directly to reflect the actions of the emperor and the court on earth; a solar eclipse, for example, might be interpreted as a sign of a forthcoming coup. The emperor employed astronomers to make nightly recordings of all celestial movements, and the official histories of China's dynasties from the second century BC onwards included a chapter on astronomy.
These are important sources for astronomers today as they might hold details of, for example, sightings of a comet over 2,000 years and so provide information about its periodicity not otherwise available.
This must have therefore been a very important and politically sensitive document, yet it was found in Dunhuang, a desert outpost of the Chinese empire, over 1,000 miles away from the imperial capital and on the ancient trading route, the Silk Road.
The scroll was one among 40,000 manuscripts in a Buddhist library cave, and lay hidden after the cave was sealed in about AD 1000 until its rediscovery in 1900. Who made it and how it ended up there will probably always be a mystery.
More information about the scrolls can be found at the International Dunhuang Project.