2019.03.12
Astronomy in the Edo(江戸) Period
Miyajima Kazuhiko 宮島一彦
(Nakanoshima Science Laboratory 中之島科学研究所)
I was asked by Dr. Soma(相馬) to talk about an aspect of the history of Japanese
astronomy in some specified time, only as a brief review. I would like to give a general talkabout astronomy in the Edo Period, and also I want to talk about the studies in which I havebeen engaged with my coworkers.
In the Edo Period when Japan gradually settled down, the import of Chinese sciencebegan active, and studies of the Shoushi li (授時暦), for example, flourished among citizens
and the motivation for calendar reform grew up both officially and privately.
Moreover, some of the Western culture was introduced through Nagasaki (⾧崎). The

Kenkon-bensetsu (乾坤辨説), a translation of a Portuguese book by Ferreira (沢野忠庵,Sawano Chuan) in 1659 and the Nigi-ryakusetu (二儀略説) written by Kobayashi Kentei (小林謙貞) in 1667 described the Aristotelian natural philosophy and cosmology. The Tianjing

Huowen (Tenkei-wakumon in Japanese 天経或問) by Youyi (Yūgei in Japanese 游藝) was
not so highly regarded in China, but it gave a big influence on Japanese astronomers such as
Shibukawa Harumi (渋川春海) as a convenient digest of the Western astronomy.
Concerning the Tianjing Huowen there are some studies on it, including that of Yoshida
Tadashi (吉田忠). Modern researchers’ evaluation about its influence on astronomy of theEdo Period is almost the same as that mentioned above. However, as the result of ourseminar on this book which were
held monthly more than about 30
years ago in Doshisha University,in which Prof. Yabuuti Kiyosi (藪内 清 ) participated regularly, it
became clear that this book was a
result of a compromise of thenew

Westernknowledge

andastronomical
Chinesetraditional astronomy, and thatmostly they are degenerate withincomplete quotations of somebooks published in China. Even
when the outline of the solar

Fig.1.The figure in the first Volume.

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system of Tycho Brahewas translated, the figurein the first volume (首巻)(Fig.1)was not the solar
system of Tycho but it isratherclosetotheso-called Egyptian system.
ThisFig.2.The so-called Egyptian system and the Tychonic system.

showsthepoor

understanding of Youyi.
Let us give another example of his wrong understanding in this book. Figure 3 shows
the structure of a model that depicts the sun and the moon revolving around the earth.
However, if the sun and the ringlet carrying themoon around are placed at the positions as
shown

in

thisfigure,neithersurfaceofrevolution of these heavenly bodies includes theearth. It is fundamentally wrong. Moreover, thephrase for explanation is misplaced and thedescription is wrong. Such system cannot explain
the apparent motions of the sun and the moonand contradicts the meaning intended in thesecond volume of the book. This shows not only
Fig.3.

the poor understanding of Youyi, but also thelower scholastic ability of Nishikawa Masayoshi(西川正休) who reproduced the original bookuncritically and incorrectly. In fact, this figure isbased on the figure in Hungai tongxian tushuo(渾蓋通憲図説), drawn by Li Zhizhao (李之藻),
which is an abridged translation of Clavius’ book,and Youyi just copied uncritically the mistake ofthe original drawing.
Irie Takahiro (入江脩敬) pointed out theincorrectness of this figure in his Tenkei

Fig.4.

Wakumon Chūkai Zukan (天経或問註解図巻)
and offered his own figure (Figure 4). However,this again shows that the motions of the sun and the moon were not correctly understood. In
the second volume (天巻), the changes of the distance and angular velocity of the moon, and2

the change of the inclination of the lunarorbit ( 白 道 ) to the ecliptic, that is, thechange in the ecliptic latitude, are described.
The period of the change of the lunar
distance is the anomalistic month, the periodof the moon moving from the ascending ordescending node to the same node is thedraconic month, and the period of the moongoing along the lunar orbit is the siderealmonth. These periods are different eachother. In the case of the instrument whose
figure is drawn in Irie’s book, we can express
the difference of the anomalistic month andthe draconic month from the sidereal month
if we slightly change the rotational period ofFig.5.

the big ring and that of the ringlet carrying
the moon. The change of the distance is essentially relative to the change of the angularvelocity and thus his system can offer a qualitative explanation. However, the anomalisticmonth and the draconic month would have the same period in his system, although they areactually different. In addition, an instrument exists (Figure 5) that is considered to havebeen made according to the figure in Irie’s book. However, in the case of this instrument, theringlet carrying the moon is attached to a big ring perpendicularly. This system can explain
the change of the moon’s latitude to the north and the south and also the change of its speed,
but cannot explain the difference of the period of the two nor the change of the distance.
In this seminar we prepared a translation and notes of the first and the second
volume(図巻・天巻) of the book, but it was not published. At present a new work groupheaded by Hiraoka Ryuji (平岡隆二) is preparing a new translation and notes of the second
volume. Kazu Tsuguto (嘉数次人) , myself and some others have been participating in it.
Recently a new document was discovered by Hiraoka, which will be included in the newpublication.
The Xuanmin li (宣明暦) was used since A.D.862 until the Edo Period, when the gap
between calendar and natural phenomena became conspicuous. The two persons wereespecially responsible for calendar reform. One is Shibukawa who was a go (碁) teacher of
the Shogunate, and the other is Seki Takakazu (関孝和) who established Wasan(和算). In
1685 Shibukawa prepared the Jyōkyō-reki (貞享暦) using the Shoushi li as a model andbased on his own observations. The Jōkyō-reki was officially used in place of Xuanmin li3

which used for 823 years. It was the first original
Japanese calendar officially used in Japan.
Shibukawa published two celestial maps, one
is called Tenshō-retsuji no zu (天象列次之図) andthe other Tenmon-bun’ya no zu (天文分野之図)
which referred to Korean Cheonsang Yeolcha Bun’ya Ji Do (Tenshō-retsuji-bun’ya no zu in Japanese
天象列次分野之図). In the latter he newly set aJapanese

bun ’ ya( 分 野 )thatisthecorrespondence between the places on the earth
and in the sky.
He applied the idea of correspondence
Fig.6. The Tenmon-keitō

between human affairs and celestial phenomena

possessed by the author.

to the Japanese social system and offereddrawings of new constellations. In 1698, he wrote them down as the Tenmon-keitō (天文瓊統,Figure 6), where the celestial map titled Tenmon-seishō (天文成象) was contained, andhe published it next year by the authorship of his son. All the positions of the stars in thismap were based on his own observations.
After the calendar reform of Jōkyō, the astronomical bureau called Tenmonkata (天文方)was established in the Shogunate, and Shibukawa was appointed the first Director General.
After that it became customary that the annual calendar was edited in the Tenmonkata whosent it to the Onmyōryō in Kyoto. They were published with annotations which we now
regard as superstition. This astronomical bureau is the origin of today ’ s National
Astronomical Observatory.
The eighth Shogun Tokugawa Yoshimune (徳 川 吉 宗 ) admitted the excellence ofWestern astronomy, and in 1720 he lifted the embargo of the foreign books, and Dutch
studies began flourishing. He expected official use of a calendar based on the Western
astronomy, but since the staffs of the Tenmonkata were incompetent, Tsuchimikado
Yasukuni (土御門泰邦), the Secretary of Onmyōryō, took back initiative and he was
successful in the enforcement of the Horyaku-reki (宝暦暦).
This calendar was not based on the Western astronomy and of inferior quality. Therefore,
Takahashi Yoshitoki (高橋至時), a disciple of Asada Goryū (麻田剛立) was appointed to astaff of astronomical bureau and he put in practice the enforcement of the Kanseireki (寛政暦) in 1799 with Hazama Shigetomi (間重富) , a senior fellow disciple. It was the firstcalendar in Japan that used the Western astronomy, but it was still a luni-solar calendar.
About Asada Goryu there are studies by Fujii Jun’ichirō (藤井準一郎) and Watanabe
4Toshio (渡辺敏夫) etc. About 20 years ago the Oita Board of Education asked Suenaka
Tetsuo (末中哲夫), Kage Toshio (鹿毛敏夫) and myself to collect Asada’s documents and towrite a critical biography. Because I was busy, I wrote only a critical biography. Although
Asada ’ s contribution is great in the history of Japanese astronomy, we cannot takeeverything affirmatively. The theory so-called “Shōchōhō” (消⾧法), namely, the change ofthe astronomical constants with time, is correct qualitatively, but not at all quantitatively.
Koide Chōjūrō (小出⾧十郎) also pointed out this already in those days. I think that theevaluation of Asada should be made taking into account this point.
Historical materials were handed down for generations by the Hazamas (羽間家) which
was a collateral of Hazamas (間家) and the historical documents that Heizaburo (平三郎)
collected had been kept as “Hazama-Bunko” (羽間文庫). About 20 years ago, they weredonated to Osaka Museum of History. They were designated as an important culturalproperty together with the historical documents in the Osaka Municipal Library in 2016.
Yoshida Tadashi, Kazu, Hiraoka, myself, and others continue to study them as “ResearchGroup of Hazama-Bunko”.
The Lixiang Kaucheng (暦象考成), in two volumes, described the solar systems of Tycho
Brahe, and the Lixiang Kaucheng Houbian (暦象考成後編) adopted Kepler‘s law for themovement of the sun and the moon although it is essentially geocentric. The Kanseireki (寛政暦) was a calendar at this level. Takahashi Yoshitoki (高橋至時) was not satisfied with this.
He translated and studied the Astronomia of Sterrekunde (Astronomie) by la Lande aiming
at further calendar improvement, but he died with the work unfinished. Ino Tadataka (伊能忠敬), who prepared the precise map of whole Japan (大日本沿海輿地全図, 1821)(completed posthumously), was a pupil of Takahashi.
Motoki Yoshinaga (本木良永), an interpreter in Nagasaki, prepared the translated book

Tenchi-nikyū-yōho (天地二球用法) in 1774 that described the Copernican theory. Shiba
Kōkan (司馬江漢) a painter and science writer, introduced to the people the Copernican
theory in his Oranda-tensetsu (和蘭天説) published in 1796 and the Kopperu-Tenmonzukai(刻白爾 天文 図解) in 1808.

Shizuki Tadao (志筑忠雄 ), an interpreter in Nagasaki,

published a translated book Rekishōshinsho (暦象新書) in 1798-1802 and introduced theNewtonian dynamics. In addition, Yamagata Bantō (山片蟠桃), a merchant in Osaka, wrote
about the Copernican theory and a solar calendar in the work Yumenoshiro (夢の代) in 1820.
However, the main interest of official astronomers was the calendar system that followed thetraditional values of China, and their interest in Copernican theory was limited to thecalendrical precision.
Kageyasu (景保), the elder son of Yoshitoki died in prison as he was involved in theSiebold affair, but the younger son Kagesuke (景佑) was adapted to the Shibuka family and5

he inherited the chair of Director of Tenmonkata and performed the Tenpō calendar reform(天保改暦) .

This calendar increased the accuracy of the position of the five planets

because it used Kepler's law.

It is the last luni-solar calendar in Japan.

Japan began using the Western calendar date after 1873 and shifted to the solar calendar,
but since the wordings of the decree that determined the leap year were not sufficient, it wasrevised in 1899, and it turned into the correct Gregorian calendar.
In addition, Buddhism had the unique cosmology Shumisensetsu (須弥山説). But thecriticism against this cosmology and Buddhism itself increased when the Western science
was introduced. The campaign for protecting Buddhism or the revival of the Buddhist
calendar became popular among the Buddhists who urgently felt danger against Westerncosmology. The priests Mon’nō (文雄) and Entsū (円通) were especially active.
Entsu wrote Bukkkoku Rekishohen (佛國暦象編), in which he insisted that all the world
calendrical systems originated in India. He devised the Shumisengi (須弥山儀) and the
Shukushōgi (縮象儀), and propagated the world-view of Mt. Sumeru. This movement
showed a considerably big upsurge and continued until about 1880.
Since 2003 I organized a study group on the five volume Bukkoku Rekishohen, held
regular meetings in Doshisha University, and prepared a translation with notes. After myofficial retirement, Hayashi Takao (林隆夫) succeeded my work, and, after his retirement,
the meeting place of this group moved to the Institute for Research in Humanities of Kyoto
University. We finished whole of the translation with notes in 2015. At present we arerevising it for publication.
When we read Bukkoku Rekishohen we can point out the following three points. (1)Logical gaps are often seen in some important places. (2) Entsū repeatedly points out that
there are two theories in the Western astronomy, namely, the new (Copernican theory) andthe old (Ptolemaic theory), and he insists that he cannot believe in the Western astronomy
since the two are mutually different. This means that he did not admit the scientific progress.
(3) He ascribes the reason why Shumisen (i.e. Mt. Sumeru) cosmology does not accord withthe practically observed phenomena to the insufficient ascetic practices of people, if one
obtains ‘divine eyes (Tengen 天眼)’ by practices, one can see it. This is against his original
purpose of the book, namely, providing scientifically correct interpretation of the Shumisencosmology.
Japan was under the overwhelming influence of Chinese science until the early Edo
Period. Later when Western science reached Japan, and its superiority became evident,
people changed the policy and became depending upon Western science. Such a historicalcircumstance seemed to have made Japanese scientific characteristics that it depends upon
the foreign country in the original study.
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