Gwansanggam: Joseon's Weather Forecasting and Scientific Innovation

About 600 years ago, in the country called Joseon, the sky was not just a blue sky or a cloudy sky.

• The role and political weight of the ‘Gwansanggam’ in Joseon
• Real historical events triggered by weather forecast failures
• How prediction failures led to scientific advancement in Joseon

Gwansanggam Bearing the Weight of the Sky

Gwansanggam (觀象監) was a core Joseon institution equivalent to today’s Meteorological Administration combined with the National Astronomical Observatory. Their main duties were to observe celestial bodies, create calendars, and forecast the weather. However, in Joseon, the sky was not simply nature. The ideology of ‘Cheonin Gam-eung Seol (天人感應說)’, meaning that if the king governs well, the heavens bless, and if not, disasters follow, dominated the state.

Because of this belief, natural phenomena like droughts, floods, and eclipses were seen as the heavens’ judgment on the king’s governance. A failed weather forecast was not just a simple mistake but was interpreted as a warning from the heavens indicating flaws in the king’s rule.

Prediction Failures and the Bureaucrats’ Dilemma

The Gwansanggam officials entrusted with this grave responsibility were mostly technical experts from the jungin (middle class). Though essential to state operations, they were often politically marginalized in a society dominated by yangban aristocrats.

Their dilemma was clear: success was expected and unremarkable, but failure brought all blame and criticism upon them. Instead of the king’s shortcomings being acknowledged, they were punished for “lack of skill,” effectively becoming political scapegoats. This resonates with modern challenges faced by scientific advisors when their expertise conflicts with political decisions.

Incidents in the Annals that Provoked Heaven’s Wrath

Case 1: Eclipse Forecast 15 Minutes Late

In Joseon, a solar eclipse was considered a direct threat to royal authority. In the 4th year of King Sejong’s reign (1422), Seowungwan (the predecessor of Gwansanggam) predicted the eclipse time, but it actually began 15 minutes later than forecast. According to the 《Annals of King Sejong》, the king and officials had to stare blankly at the sky in the palace courtyard for 15 minutes, and the responsible official, Lee Cheonbong, was eventually punished with a cane.

Case 2: Rain Prayers Without Response

As an agricultural nation, drought in Joseon meant a survival crisis. When rain did not come, the king performed Giuje (祈雨祭), a rain prayer ritual, and practiced self-restraint such as reducing the number of side dishes in meals (Gamseon (減膳)), blaming his own lack of virtue. In such times, officials sometimes used drought as a pretext to criticize the king’s policies or attack political rivals. Thus, weather phenomena became a battleground beyond science, deeply entangled in political conflict.

The Paradox Born of Failure: Sparks of Scientific Revolution

Did you know that all these failures actually became a catalyst for scientific progress?

Repeated forecast failures, especially eclipse prediction errors due to discrepancies with the Chinese calendar, posed a significant political burden for King Sejong. To resolve this, Sejong ordered the compilation of an independent calendar system, 《Chiljeongsan (七政算)》, which accurately calculated celestial movements based on Joseon’s capital, Hanyang.

Incorporating the latest Islamic astronomy of the time, 《Chiljeongsan》 was a great achievement of Joseon science born from a political crisis caused by prediction failures. The attempt to read the will of heaven evolved into a scientific inquiry to understand the laws of the heavens.

This innovation did not stop there. In the late Joseon period, the introduction of the Shixian calendar (時憲曆), brought by Western missionaries, further improved accuracy. It is fascinating how political necessity led to continuous investment in science and technology. When I first learned this, I realized once again how great innovation can arise from the pressure of failure.

Conclusion

The story of Gwansanggam in Joseon teaches us three important lessons:

1. The fusion of science and politics: Astronomy in Joseon was not just an academic pursuit but a key political tool to legitimize royal authority and state governance.
2. The burden of responsibility: The blame for forecast failures fell heavily on Gwansanggam officials, determined more by political impact than the scale of scientific error.
3. Innovation through failure: Repeated prediction failures paradoxically became a powerful motivation for independent scientific and technological advancement, such as the 《Chiljeongsan》.

Ultimately, Joseon’s effort to read the will of heaven led to a scientific quest to understand the laws of the heavens. This historical lesson shows that failure is not merely an end but can be a catalyst for great progress.