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The Kitora Tomb, located near the village of Asuka in Japan's Nara Prefecture, is known for gorgeous, colourful paintings at the four cardinal points of the compass. A black tortoise guards the north of the ancient tumulus, which has been standing since the seventh or eighth century. A red phoenix stands at the south, a white tiger at the west and a blue dragon at the east.

The ceiling of the tomb is decorated differently, with a map of the night sky, charting 68 constellations, with the stars picked out in gold leaf. Three concentric circles are drawn with vermilion, showing the movement of celestial objects, one of which is the sun.

According to Kazuhiko Miyajima, a professor at Doshisha University who studied the chart after the tomb was discovered in 1998, this makes it possibly the oldest astronomical chart of its kind in the world. It has designations for the horizon, equator and ecliptic circles, as well as recognisable patterns of stars.

While older depictions of the skies have been found in the west (the 17,300-year-old Lascaux cave painting, for example, shows Pleiades, Taurus, Orion and Aldebaran), most do not contain recognisable star patterns, or diagrams of astronomical phenomena.

One thing that has baffled researchers, however, is the area of sky the chart depicts.

Researchers Mitsuru Soma, an assistant professor of astronomy at the National Astronomical Observatory of Japan, and Tsuko Nakamura, a researcher of modern astronomy with Daito Bunka University's Institute of Oriental Studies, teamed up with Japan's Agency for Cultural Affairs and Nara National Research Institute for Cultural Properties to calculate the location, reports The Asahi Shimbun.

The two researchers worked separately, and determined that the sky as depicted in the Kitora Tomb chart was seen from China, from locations such as modern-day Xi'an and Luoyang.

They also determined that the chart showed the sky as it would have appeared several hundred years before the construction of the Kitora Tomb -- although they didn't agree on the number of years. Soma said that it shows the sky as it would have appeared between 240 and 520, while Nakamura said it would have appeared so between 120BC and 40BC.

Miyajima believes differently, extrapolating that the chart shows the sky as it would have appeared in 65BC, either from Pyongyang or Seoul, the capitals of North and South Korea respectively. In his 1999 lecture, he had said that the chart had probably come from Korea, but showed the sky in China.