Futian li 符天曆 calendar

Futian li (calendar) 符天曆. Also 符天歷, 合元萬分歷, 曹公小歷 and 小歷. A popular calendar (i.e., not officially published by the state) compiled by Cao Shiwei 曹士蒍 (d.u.) in the Jianzhong 建中 period (780–783) of the Tang, known originally even in pre-modern times as having been based on Indian calendrical methods 天竺歷法. This is reported in the Xin wudai shi 新五代史 (fasc. 58), which further states its starting point 曆元 is year 5 of Xianqing 顯慶 (660). This is close to the starting point of the Navagraha 九執曆: year 2 of Xianqing (657) (see Yabuuchi translation 1989). The Futian li establishes the solar year 回歸年 as 365 days + 2448/10000 days.

It was initially only in popular, not official, use until it was named the Tiaoyun li 調元歷 (or it was otherwise based on the Futian li) and employed for five years under the Later Jin 後晉 (936–946) between 939–944 (see also Liao shi 遼史, fasc. 42). This is echoed by the Kunxue jiwen 困學紀聞 (fasc. 09) which also notes Wang Pu 王樸 in the Later Zhou 後周 (951–960) abolished study of the Futian li. The Song shi 宋史 (fasc. 207) and Chongwen zongmu 崇文總目 (fasc. 4) list it and a few related works. See also the additional remarks in the Yu hai 玉海 (fasc. 10). The alternate title He yuan wanfen li 合元萬分歷 is noted in the Junzhai dushu zhi 郡齋讀書誌 (fasc. 13). The Yuan period (1279–1368) Mishu jianzhi 祕書監志 (under 二夕軒八斤入兩) reports the Futian li and the Xuanming li 宣明曆 as texts to be studied and examined, demonstrating that the calendar was actively studied until this period. Both calendars were also jointly consulted in Japan.

It seems the calendar initially did not account for the Indian pseudo-planets Rāhu 羅睺 and Ketu 計都. Song Lian 宋濂 (1310–1381) in the Luming bian 祿命辨 reports that early in the Zhenyuan era 貞元 (785–805) after production of ephemerides for the eleven stars by Li Biqian 李弼乾 (otherwise Li Miqian 李彌乾), which was when the Duli yusi jing 都利聿斯經 was also translated, Cao Shiwei additionally calculated ephemerides for Rāhu and Ketu starting from year 1 of Yuanhe 元和 (806). The Zhizhai shulu jieti 直齋書錄解題 (fasc. 12) also records a specific work entitled Luoji er yinyao licheng li 羅計二隱曜立成歷 (an ephemeris for Rāhu and Ketu) by Cao Shiwei, noting the start date. This possibly explains why the Buddhist Qiyao rangzai jue 七曜攘災決 (T 1308) has a separate starting date for Rāhu and Ketu: the calendar therein commences from 794 for the five visible planets, and 806 for Rāhu and Ketu (Yano 2013: 174–185 and Yabuuchi 1982: 5–6). The calendar also cited therein called Qiyao xinfa 七曜新法 is possibly referring to the Futian li. Additionally, the Zhizhai shulu jieti also mentions a Tang Xianqing li 唐顯慶歷, which is probably the Futian li.

Despite the Tang law codes (Tanglü shuyi 唐律疏議) expressly forbidding private study and possession of astronomical works (see article #110 in fasc. 9), unofficial calendars proliferated following the breakdown of central state authority after the An Lushan 安祿山 rebellion (755–763). Additionally, the introduction of horoscopy in the first years of the ninth century required accurate means of determining past positions of all nine planets 九執, a function which the Futian li fulfilled. It was also influential in Japanese Buddhist astrology (see Sukuyōdō 宿曜道). Fragments of the calendar are preserved in the Japanese Futenreki nittensa rissei 符天曆日躔差立成 which is included in the Tenmon hisho 天文祕書 (Suzuki 1998). See also Dunhuang 敦煌 document Pelliot chinois 4071.


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[Jeffrey Kotyk; source(s): See Bibliography]