(b Kyoto, Japan, 27 December 1639; d. Edo [now Tokyo], Japan, 11 November 1715)
Harumi was the son of Yasui Santetsu, a professional go player in the service of the Tokugawa shogunate. After his father’s death he assumed his name and profession, becoming known as Yasui Santetsu II. Trained in go, Harumi studied Chinese and Japanese classics, Shintoism, and calendrical astronomy with various teachers. His distinguished service in calendar reform led to his appointment in 1685 as official astronomer. He later returned to his original name, Shibukawa.
The Chinese lunisolar Hsuan-ming calendar, adopted in Japan in 862, had not been reformed for more than eight hundred years. Over the centuries the discrepancy in the length of a solar year had increased so that by Harumi’s time there was a two-day delay in the winter solstice. Moreover, it had become of little use for its traditional purpose, the precise prediction of solar and lunar eclipses. Although the error caused little inconvenience or confusion in daily life, reformation of the official calendar became an event of major political importance–to strengthen the prestige and authority of the imperial court vis-à-vis the shogunate by providing the people with an accurate calendar.
An able mathematician and skilled diplomat, Harumi urged calendar reform by pointing out faults in the Hsuan-ming calendar, seeking to prove the discrepancy by actual observation of winter and summer solstices and by demonstrating the possibility of establishing a calendar that would be more accurate–as confirmed by observation–in predicting eclipses.
In 1669 Harumi began conducting astronomical observations, probably the first systematic observations made in Japan. Following the procedures of traditional astronomy, he set up a gnomon and measured the lengths of shadows at various points before and after the winter solstice, in order to calculate the time of occurrence. He was especially interested in the Shou-shih calendar of the Yüan dynasty (1279–1368), a crowning achievement of calendrical astronomy adopted in China in 1282; and his observations were based upon its methods.
In 1673 Harumi proposed to the emperor the adoption of the Shou-shih calendar. In a report entitled “On the Eclipses” he compared the differing calculations, derived from both calendars, of solar and lunar eclipses, for the period 1673–1675. Of the six subsequently observed eclipses, however, the solar eclipse of 1675 was found in better agreement with the calculations based on the Hsuan-ming calendar.
Stunned and disheartened by this experience, Harumi improved his calculations and subsequently devised a calendar that agreed with the incorrectly predicted eclipse, In 1683 he again proposed a calendar revision to the emperor, the first calendar devised by a Japanese that was completely independent of the Chinese calendars.
However, the tendency of Japanese astronomers to follow Chinese practice was not easily overcome. In 1684 the fifteen-member Board of Astronomy decided to adopt a newer Chinese calendar, the Ta-t’ung. Appalled by this decision. Harumi engaged in some quiet behind-the-scenes maneuvering and finally succeeded in reversing the decision. Later that year his own calendar revision (the Jokyo calendar) was implemented.
Like the Shou-shih calendar, the Jokyo incorporated the secular variation term of the length of the tropical year. Such correctional terms were used to explain the records of winter solstices in the remote past. The Ta-t’ung, although following the substance of the Shou-shih, had abandoned secular variation terms in the belief that such minimal revisions could not be proved by observation; Harumi’s own adoption of them was based on his conviction that it would render his calendar more profound.
The Jokyo and Shou-shih calendars can be considered the culmination of traditional Chinese calendrical astronomy, distinguished–like Babylonian astronomy–in their concentration on numerical and algebraic matters. Neither used the geometrical approach or the schematic model of Western astronomy, and thus, taken together, neither surpassed Ptolemy’s Almagest.
During his career, the Shih-hsien calendar, compiled by Jesuits, had been introduced in 1644 in China, and Harumi frequently referred to it. There was, unfortunately, no way for him to learn about the system adopted in compiling it. The Japanese government’s closed-door policy, begun in the 1630’s, included a ban directed mainly against Jesuit writings and prevented him from obtaining an important work on Sino-Jesuit astronomy, Hsiyang hsin-fa li-shu (“Treatises on Calendrical Science According to New Western Methods.” 1645).
In his references to Western theory, Harumi based his information exclusively on Tien-ching huo-wen (“Queries on the Classics of Heaven,” 1675), by Yu I. Rather than a scientific treatment of observational values or of the methods of calculation derived from them, the work was merely a popular explanation of various astronomical and cosmological theories. Harumi was especially impressed by its clear explanation, using a geometrical model, of eclipses, which he had never found in Chinese calendrical writings. Yet, as an astronomer focusing on useful parameters or numerical values that could be borrowed to improve the precision of a calendar, he found the work disappointing and came to regard Western astronomers as “barbarians who may have theories but cannot prove methods.” It is regrettable that sufficient material for evaluating Western theories was not available to him.
During the eighteenth century Japanese astronomy altered its orientation from China to the West. Harumi belonged to the first generation of astronomers who, with only limited knowledge of Western astronomy, began evaluating the merits of both systems. He was a leader of those Japanese astronomers who, throug their science. initiated the acknowledgment of Western superiority and the modernization of Japan.
In English, see Shigeru Nakayama, A History of Japanese Astronomy, Chinese Background and Western Impact (Cambridge, Mass., 1969).
In Japanese, works on Harumi and his work are Endo Toshisada, “Shibukawa Harumi,” MS preserved at the Japan Academy, begun in 1904; Shigeru Nakayama, “Shibukawa Harumi’s Solstitial Observation and the Hsiao-chang Method,” in Tenmon Geppo, no. 58 (1965); and A History of Japanese Astronomy, Chinese Background and Western Impact (Cambridge, Mass., 1969); Nishiuchi Masaru, Study of Shibukawa Harumi (Tokyo, 1940); Shibukawa Takaya, “Biography of Master Harumi,” in Nihon Kyoiku Shiryo9 (1889); and Jinzan Shu (Tokyo, 1909); and Watanabe Toshio, Shibukawa Harumi, the Pioneer of Japanese Calendrical Astronomy, and the History of Astronomy in the Edo period (Tokyo, 1965).