Can a country compute its own sky?

That time, that place

Joseon used the calendar it received from Ming China. But a calendar is computed for the latitude and longitude of the place that observes. Take tables calculated for Beijing and apply them in Hanyang and sunrise and sunset fall out of step, and eclipse predictions miss.

Early in Sejong's reign an eclipse prediction failed and the official responsible was punished.

Why this question

To move someone else's sky onto your own, you must change the reference point of the calculation itself. And to change the reference point you must know the principles the calculation runs on.

Copying tables will not do. Only understanding lets you recompute.

What was found

Sejong set scholars such as Yi Sun-ji and Kim Dam to work through the sources — the Chinese systems, and the Islamic tradition as well.

The result was the Chiljeongsan. Its inner volume recomputes the Chinese calendar for Hanyang; its outer volume digests and sets out the Islamic astronomical system. The latitude of Hanyang was measured directly and taken as the reference, and the positions of the Sun, Moon, and five planets could now be calculated independently.

At the time, the countries able to compute a calendar from their own position could be counted on one hand.