He had a philosophical background in Neo-Confucianism that originated from the Song dynasty (960~1279 AD) of China . The Neo-Confucians revolutionized the Buddhists’ Goryeo dynasty to establish the Joseon Dynasty.

  The planisphere was carved in order to justify the revolution. The founders of the Joseon dynasty tried used the reproduction of the planisphere of the ancient powerful kingdom as a sign that heaven sanctioned the new kingdom. The names on the planisphere show the new winds of change.

  Neo-Confucianism was based on the deep understanding of the nature and advanced capitalism prevalent during the Song dynasty. However, to modern sociologists it looks more like materialism. There were many natural philosophers during the era of the Northern Song dynasty (960-1127 AD).

  You might also be surprised to know that the public clock towers in the main squares of European cities originated from clock towers built in China during the Song and Yuan dynasties. The Chinese clocks were clepsydras or water clocks, while European clocks used pendulums or mechanization.

  The famous Korean engineer, Chang Young-Shil, made a fully automatic typical clepsydra during the King Sejong era in the 15th century. Small models of the Sun and the Moon moved along the ecliptic while miniature dolls appeared to ring a bell or drum to notify the exact time every hour. The present-day 24-hour time system originates from those Chinese and Korean clepsydras.

 The elder brother of the grandfather of Kwon Keun is Kwon Jun (權準, 1281~1352 AD), whose tomb was excavated in 1993. On top of the stone coffin, 28 Shu were painted, corresponding to the 28 constellations lying in the ecliptic region. These 28 Shu are lunar houses corresponding to the zodiac. It is the tradition of Goguryeo (高句麗 37 BC ~ 668 AD) to paint constellations on the walls of tombs.    Goguryeo was referred to as Goryeo (高麗) after the 5th century; this name was then inherited by the 10th century Korean people who established the Goryeo dynasty. As a matter of fact, they painted frescos in the tomb again after the decline of Goguryeo in 668 AD.

  The contents and motives of their painting are very similar to those of Goguryeo. According to the Royal Chronology of the Joseon dynasty (Joseonwangjosillok), constellations, the Sun, the Moon, and the Milky Way were painted in the tomb of the wife of King Sejong. This was also inherited from their ancestors. However, King Sejo, the second son of King Sejong, prohibited people from building mural tombs made of stone. Thus, the tradition of painting mural frescos faded away.

 According to the inscriptions, Seol Kyeong-soo wrote these Chinese characters. His family emigrated fromMongolia during the Yuan dynasty. It’s likely that they originally came from Central Asiaor the regions between far-Western China and Pakistan .

  In the Yuan dynasty, Seol Kyeong-soo’s family was part of the intelligentsia, playing an important role in science and technology. After the decline of the Yuan dynasty, his family escaped from China , with some family members going to the Goryeo dynasty. According to the Royal Chronology of the Joseon dynasty (朝鮮王朝實錄), ministers objected the fact that foreign techocrats wore their own ethnic clothes, instead of official uniforms of the Joseon dynasty. From this, we can see that Korean ancestors hired foreigners as far back as six hundred years ago.

  Another surprising fact is that this planisphere originated from a planisphere of the Goguryeo Kingdom . According to the inscriptions of the planisphere, its prototypical map originated from the Goguryeo era (37 BC ~ 668 AD). The inscriptions says:

  “There was a person who presented a copy of an original planisphere that had been forgotten after it sank into the river in Pyong-Yang during a war. So much time had passed that the angular positions of stars in the ancient planisphere became different from the present positions. Thus they recalculated and carved stars on their correct positions.”

  Goguryeo located in present Dongbei three provinces of the People’s Republic of China and North Korea in the Korean peninsula. Goguryeo was changed to Goryeo (高麗) after the 5th century. Goguryeo declined in 668 AD under the allied forces of the Shilla and Tang. Later, the Goyreo dynasty established in 918 AD succeeded the Goguryeo. The present-day name of KOREA originated from the Goryeo dynasty known to Europe and the Middle East .

  Pyong-Yang, the current capital of North Korea , had been the capital city of Goguryeo between the 5th century and the 7th century. Thus, we conclude that the original planisphere was inherited from the ancient Goguryeo Kingdom .

  The oldest Chinese planisphere remaining today was made in the Song dynasty in AD 1247. Can you imagine that the Goguryeo people could make such a planisphere at least six hundred years ago? The answer is definitely yes. Goguryeo people painted vivid frescos in tombs of their kings and nobles. Upon seeing these pictures one gets a strong feeling that the Goguryeo people had both a keen interest in heavenly bodies and a high level of astronomical knowledge.

  Constellations and the abstract symbols that stand for the heavenly bodies or astronomical concepts were painted. Some constellations can be thought to reflect their own culture, while there are some Chinese constellations with their names written by themselves. Moreover, there are frescos that display legends about constellations. Thus, the existence of a planisphere in the Goguryeo era is not so unbelievable.

  We were even more surprised when the Kitora mural paintings were excavated in 1998. Using an endoscope, Japanese archeologists obtained images of wall paintings in the tomb. They found a large planisphere on the ceiling of the tomb. The planisphere is a twin of the Joseon planisphere. Both of them have three large concentric circles and one eccentric circle. Also, the constellations and linkages are similar to the Joseon planisphere, while they are quite different from those in the Chinese planisphere of 1247 AD.

  The three concentric circles represent the circumpolar region, the equatorial line, and the southern horizon. The ratios of radii of these circles for a region of latitude are different from those for a region of another latitude. The circumpolar radius is zero at the equator, while three lines overlap at the North Pole. Therefore, we can calculate the latitude of the place of observation of the planisphere.

The latitude of the Kitora planisphere is about 40 degree north. It is a good assumption that the observation was made in the capital city of a certain kingdom. On this assumption, Pyong-Yang, the capital city of Goguryeo is the only candidate where the Kitora planisphere could have been made. Thus, we see that the original Goguryeo planisphere was imported into ancient Japan .

  We can apply the same analysis method to the Joseon planisphere. We first found that its map projection is the polar equatorial and equidistance projection: the linear distance of an object on the map from the center is linearly proportional to the north polar angular distance. A statistical analysis shows us that the circumpolar stars whose declinations are larger than 50 degrees are at the epoch of about 1300 AD.

  On the other hand the upper culmination of stars whose declinations are lower than 50 degrees are at the positions of the epoch of the first century. In conclusion, we can confirm the reliability of the inscriptions on the map, and prove that the prototypical map of the Joseon planisphere was made during the Goguryeo era.

  We can also see ancient theories on the structures of the Universe in the inscription of the planisphere. These same sentences can be found in ancient Chinese history books. There were six major theories on the structure of the Universe in the ancient times. One theory was Hon-cheon-seol. The Universe is something like an egg. The Earth is the an egg yolk, while the atmosphere is the albumen. The sky is similar to the eggshell. The sky is hard, and heavenly bodies are attached beneath the eggshell. The shell rotates, and so the stars are seemingly moving.

  Another theory was Seon-ya-seol, in which stars and planets are believed to move in free space. This is closer to the modern view of the Universe. However, it was Hon-Cheon-Seol that was officially accepted by rulers in China . 

  One ancient masterpiece reminds us of the long history of Korean astronomy, and the international exchange of scientific ideas and human resources. You can see the planisphere at the National Palace Museum of Korea and the Memorial Museum of King Sejong in Seoul . These museums highlight the best opportunities to see relics of Korea ’s rich cultural history.