How do you restore a star map that burned?

That time, that place

Soon after founding Joseon, Taejo ordered a map of the heavens. A dynasty claiming heaven's mandate had to show it could handle the sky.

But there was no base map. Goguryeo had a star chart carved in stone; it was said to have been lost in the Daedong River when Pyongyang fell.

Why this question

What survived was a single rubbing taken from that stone. But there was a problem: star positions drift over centuries, because the Earth's axis wobbles slowly, like a spinning top.

Carve an eight-hundred-year-old map as it stands and it will not match the sky.

What was found

In 1395 the royal astronomers used the rubbing as a base but recomputed the positions for their own time, and cut 1,467 stars into stone.

Modern analysis found two epochs mixed in the chart: some constellations match the sky of around the first century, others the late fourteenth. The tradition turned out to be true.

The map is on the back of the ten-thousand-won note.