Rosa Mui and Paul Dong: Ancient Chinese Astronomer Gan De Discovered Jupiter’s Satellites 2000 Years Earlier than Galileo
A record of an ancient Chinese astronomical observation has caused Galileo to lose his credit as the discoverer of Jupiter’s satellites. According to Professor Xi Zezong, a Chinese astronomical history research specialist in Beijing, mankind’s discovery of Jupiter did not depend on the telescope but on naked human eyes. The record of this observational reality was not made in Europe during the Renaissance three hundred years ago by Galileo, but more than two thousand years ago by the ancient Chinese astronomer Gan De. Chinese scientists have verified Zezong’s claim and the international astronomical community is providing further proof. Galileo, it can be said, has lost his “gold medal.”
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It is commonly asserted that the four large satellites of Jupiter (that is, Satellites No. 1, No. 2, No. 3 and No. 4, called Io, Europia, Ganymede, and Callisto) were first discovered by Galileo in 1610. There is a known contender in the West, the German astronomer S. Mayer. Some scholars, after careful investigation, hold that he discovered the satellites ten days earlier than Galileo. Consequently, Mayer and Galileo are both sometimes considered as discoverers of the four large satellites of Jupiter. These opinions, however, are now no longer completely correct because, according to Xi Zezong of the Research Institute of the History of Natural Science, Chinese Academy of Sciences, a Chinese astronomer named Gan De had already discovered Jupiter’s satellites two thousand years before Galileo.
Xi Zezong is a research fellow of the Institute for Research in the History of Natural Science at the Chinese Academy of Sciences. He is also a council member of the Chinese Astronomers’ Association and an authority on Chinese astronomical history. In October 1980, at a forum on the technological history of natural science held in Beijing (Peking), he first stated his position. The basis of it is found in Vol. 23 of the ancient Chinese astronomical work Kai Yuan Zhan Jing (Books of Observations from the Beginning of History). A passage in it reads: Gan De said, “In the year of Shan Yu, Xi, Nu, Shu, and Wei*. It was very large and bright. It seemed that there was a small “red star” attached to its side. This is called an alliance.”
“The annual star” was the ancient Chinese name for Jupiter. In contemporary language, this passage means that “there was a small pink star beside the planet Jupiter. We, therefore, conclude that this is a satellite of Jupiter.” It is evident that Gan De had already seen with his naked eyes the satellites of Jupiter.
*Xu (Io), Nu (Europia), Shu (Ganymede), Wei (Callisto)
When I first became aware of Zezong’s assertion, I contacted him and asked for a more detailed explanation. He told me that Jupiter was called the annual star in ancient China because the circuit of Jupiter’s revolution around the sun takes twelve years. If we divide up the sky into twelve sections, Jupiter will move annually in one of these sections. Consequently in our ancient times, the locality of Jupiter – one of the brightest lights in the sky – was taken as a basis for the reckoning of years. Each year is denominated by the section of sky in which Jupiter moves. It is called the reckoning of years according to the annual star. This annual star reckoning was very commonly used in the “Warring States” (403-221 B. C.) periods in China more than two thousand years ago. The historical work Zuo Chuan (Records of the Spring and Autumn Era), completed in about fourth century B. C. and recorded especially important events in the various feudal states in the “Spring and Autumn” period (479-256 B. C.) had many records with the years indicated by the annual star reckoning system. Because of the special usefulness of Jupiter, it was given particular attention in astronomical observations at the time. In the “Warring States” period, Gan De had written the Book of the Annual Star. Unfortunately, this book together with his other astronomical work Tian Wen Xing Zhan (Star Observation) is now lost. Only in Kai Yuan Zhan Jing, compiled by the Tang Dynasty (670-905 A. D.) astronomer Jutan Xida, are many of Gan De’s original words still preserved.
Since this record is taken from the work of a Tang Dynasty astronomer, why could it not have been recorded in the later Qin Dynasty (255-209 B. C.) or Han Dynasty (206 B. C.-220 A. D.) period? Why must it be a record of observation made in the “Warring States” period? Zezong pointed out the following confidently: judging from the term”alliance”, we concluded that it was a record of an observation made in the “Warring States” period, the various feudal states, according to their “vertical” or “horizontal” political policies, were busily engaged in making alliances. Consequently, the term “alliance” was most frequently used in those periods. In Zuo Chuan alone, the term “alliance” appeared nineteen times. It does not appear in books written before then and was also very rarely used in the Qin and Han Dynasties.
Furthermore, Zezong said before and after the above – quoted passage from Kai Yuan Zhan Jing, there are twelve continuous records of the positions of Jupiter. Compared with the list of the movements of stars obtained by electronic calculators at present, we can conclude that the most suitable time for the occurrence of Gan De’s observation was 364 B. C. in the “Warring States” period. This analysis by Xi Zezong received the wholehearted support of Professor Wang Zhenduo of the Chinese Historical Museum.
Zezong told me, “The book Kai Yuan Zhan Jing as a very rarely seen ancient Chinese astronomical work is now on the shelves of every large library. Then why has such an exact and important record not attracted the attention of astronomers before now? The reason is very simple: historical tradition in science history. According to the traditional viewpoint, the satellites of Jupiter were first seen by Galileo through a telescope. If anyone wished to see them, he must use at least a small telescope. It was presumed that the satellites cannot be seen by naked eyes. Everyone thought so because books on astronomy said so. Consequently, Gan De’s record has been overlooked.”
As a matter of fact, this record by Gan De had received Zezong’s attention as early as 1957 and he had discussed it with certain other people. However, owing to the fetters of traditional viewpoints, they did not really pay serious attention to Zezong, not to speak of making any further investigation and research.
In 1980 when Zezong saw the book Popular Astronomy by the well-known French astronomer, C. Flammarion, he again thought about the record made by Gan De. Flammarion wrote, “At least satellites’ No. 3 and No. 4 of Jupiter can be seen by the naked eye.” Later, Zezong found an interesting account in the works of the great German scientist Frederich Alexander Humboldt. Humboldt said that he knew a tailor named Schon, who when young, could see directly with his naked eyes the fourth satellite of Jupiter, but when he grew older, he could no longer do that. With this information, Zezong had comparatively more ground to maintain that the Chinese astronomer Gan De had seen Jupiter’s satellites because in Gan De’s time, the pollution of the air was far less than it is at the present, and the effect of artificial lighting on nighttime visibility was also negligible.
After Xi Zezong reported his findings, he received research support from several administrators. Two activities were then undertaken. The first was an experiment made in October 1980 to carry out an imitative observatory’s planetarium. Data showed that at least satellites’ No. 3 and No. 4 of Jupiter could theoretically be seen by the naked eyes because the least bright stars visible to the naked eyes are the sixth-class stars, and the brightness of the four satellites of Jupiter is either of the fourth or fifth class.
The next activity was to organize young people to make experimental observations because according to the record of Humboldt, the tailor Schon could see Jupiter’s satellites when he was young. The time chosen was in accordance with the record of the book Kai Yuan Zhan Jing,that is, when the planet appeared to be very large and bright, the time when Jupiter was nearest to the Earth. The astronomical almanac indicated that the middle ten days of March 1981, fulfilled this condition. The Institute for Research of the History of Natural Science then organized ten middle-school students, teachers and scientific research workers to proceed to the Xing Long Observation station, Hebei Province, a branch of the Beijing Observatory, to try to view Jupiter with their naked eyes. The result: eight persons saw the pink satellite No. 3 of Jupiter on two consecutive nights and three students saw satellites No. 1 and No. 2. Since satellite No. 4 was then on the back of Jupiter, it could not be seen. The conditions observed agree completely with the record of Gan De.
These two experiments, however, still did not completely convince everyone at the Institute and the Observatory, who were doubtful of the conclusion. In order to exclude the influence and to make an objective examination of the actual conditions of the observation of Jupiter by naked eyes, the Beijing Observatory adopted an experimental testing method of observation by imitating human eyes and recording the result of the observation of Jupiter by means of photography.
The instrument used was the double-barreled astrograph of the Xing Long Observation Station, which has a caliber of 40 centimeters and a focal distance of 200 centimeters. The film used was Kodak 103a? with a granular diameter of 25 microns. The angular resolving power of the telescope than was 2.5 angular seconds. It is known that the scope of adjustability of the human pupil is 1-8 millimeters. Taking the bore of the human pupil in looking at things in the dark to be 6 millimeters, an imitation pupil light barrier with a caliber of 6 millimeters was placed at the center of the frontal part of the objective lens of the astrograph. The resolving power of the diffraction angle of a then telescope at that time was 20 angular seconds, which was the same as the maximum resolving power of the human eyes in dark surroundings.
An astrograph so equipped may positively be taken as an imitation human eye. It can quite successfully imitate the effect of the diffusion of light on the retina of the human eyes. The result was on May 27, 1981, the images of Jupiter and its four brighter satellites were clearly shown on a Kodak 103a? film after an exposure of 60 minutes. This experiment objectively tested the possibility of the observations of Jupiter’s satellites by the human eyes. It proved definitely that human eyes are capable of seeing the satellites of Jupiter, especially the pink satellite No. 3.
Thus, the validity of Gan De’s record was substantiated. The great majority of Chinese astronomers then also took an affirmative attitude toward Zezong’s argument. In 1981, when Mr. Li Jing, assistant research fellow of the Beijing Astronomical Observatory, participated in the “Sixth Physics and Modern Requirements Summer Forum” in Pakistan, he took Zezong’s discovery as the subject of his discourse and won a tremendous reaction because with a single stroke, he pushed forward mankind’s recognition of satellites, with the exception of the moon, by two thousand years.
When Zezong’s discovery was reported by Chinese journalists, it attracted the attention of many foreign astronomers. From April to June in 1981, Zezong gave lectures in Tokyo University, Kyoto University and Kansai University in Japan. The record of observation made by Gan De and the experiments of Chinese astronomers aroused great interest in Japanese scholars. Mr. Kiyoshi Yabuuchi, Honorary Professor of Kyoto University and an authority of Japanese astronomical history, gave a very high praise to Zezong’s discovery and considered it as the trial beginning of experimental astronomy. He said, “To repeat now once again the method used in ancient records is a key to the solution of many prehistoric and ancient problems. There are many things in astronomical history which can be done by going along this direction.”
At the sixteenth International General Assembly on Scientific History held in August 1981 in Romania, Zezong’s report also received like a stone thrown into the water, stirring up a thousand layers of waves. Professor Maeda of the Japanese Sociology Department said that he himself had seen the satellites of Jupiter with his naked eyes when he was young. Dr. Brichers, Professor of Astronomy of Boston University, testified that he knew two astronomers, Mr. Barnard and Mr. Shapeio, who had seen the satellites of Jupiter with their naked eyes but people at that time did not believe them.
Last year, Professor Joseph Lee, who was very zealous in the study of the development of science in ancient China, wrote an article praising the discovery of Zezong and said with deep feeling that in the vast ocean of ancient Chinese literature, there are still innumerable things of great value waiting to be sorted out and studied.
China is an age-old country with a civilization of more than four thousand years. In science, literature, philosophy, history and various other lines of work, it has made indelible achievements. The work of astronomical observation is a most glorious chapter in ancient Chinese astronomy. The earliest records can be traced to the book Shang Shu (Book of History) completed about two thousand years B. C., a work of political literature recording the legendary events from the times of Emperors Yao and Shun down to the Western Zhou Dynasty. Moreover, it is generally acknowledged by astronomers around the world that the richness and accuracy of ancient Chinese records of astronomical observation occupy the first place in the world history of astronomy. Many astronomical phenomena, such as the solar eclipse, comets, new planets, black spots on the sun, meteor showers, the appearance of the Venus at noon (i. e. the visibility of the planet Venus to naked eyes at its brightest aspect), the plentiful and accurate records of astronomical observation not only occupy a very high position in the world history of astronomy, but are also of important reference value to the development of modern astronomy. Zezong’s discovery of the record about Jupiter’s satellites in the vast ocean of ancient Chinese books has undoubtedly added another brilliant pearl to the already fully jeweled crown of China.