Lixue yiwen 曆學疑問

Lixue yiwen 曆學疑問 is a book on astronomy written during the early Qing period 清 (1644-1911) by Mei Wending 梅文鼎 (1633-1721), who also compiled the collection Lisuan quanshu 曆算全書.

The book of 3 juan length was finished in 1690. It consists of over fifty chapters, all presented in a question-and-answer format to introduce and discuss astronomical theories. It explains complex concepts in a clear and accessible way, making it a rare work that appeals to both experts and general readers alike.

The book explores how the development of calendars has evolved from simplicity to precision, with modern methods surpassing ancient ones. It highlights commonalities between Chinese and Western calendrical systems by citing five key examples, such as the Western concept of planetary maximum elongation corresponding to the Chinese idea of waxing and waning, and the Western notion of stellar motion aligning with the Chinese concept of precession. It also discusses major distinctions between the Chinese and Western calendars, including differences in lunar calculations, the starting points of the solar day, and methods of intercalation; the exactness in measurements by Western scholars; structural and specific differences between Islamic and Western calendars; epoch truncation; the belief that the Xia Calendar dates back to the time of mythological rulers Yao 堯 and Shun 舜; the concept of a spherical Earth; the ancient Chinese cosmological model wherein the heavens resemble a dome covering a dish-shaped Earth; astronomical instruments described in the Zhoubi suanjing 周髀算經; the Western practice of continuous year counting; the determination of the year's length; variations in residual year fractions; altitudes of the sun, moon, and five visible planets; the Western "static sky" theory; the theory suggesting that the heavens rotate counterclockwise; the need to define an ecliptic pole; the obliquity of the ecliptic at about 47 degrees; Western theories of celestial coordinates and their intersection with the zodiac; the comparison of the Chinese system, which divides the celestial sphere into 365¼ degrees, with the Western 360-degree system; the Western concept of the sun's varying height as an equivalent to the Chinese idea of waxing and waning; the epicycles; and the variability of a planet's velocity in movement, influenced by its distance from the earth and the sun.

Although the book is structured as a series of questions and answers without a rigid system, it can be broadly categorized into the following major sections: Models of the structure of the universe, including the Chinese, Western, and Islamic perspectives; the traditional Chinese concept of the heavens as a dome covering the Earth (gaitian 蓋天); ancient Chinese astronomical and calendrical theories and calculations in comparison with the West and Islamic models, the introduction of Western astronomical methods, with a focus on their scientific advancements. Mei Wending demonstrates a profound and comprehensive understanding of Chinese and Western calendrical sciences. His explanations provided a fresh perspective, presenting astronomy in a way that felt both innovative and all-encompassing.

The text is included in the series Mei Wu'an Xiansheng lisuan quanshu 梅勿庵先生曆算全書 and Meishi congshu jiyao 梅氏叢書輯要.

A supplement of 2 juan called Lixue yiwen bu 曆學疑問補 was finished in 1705.

Unlike the Lixue yiwen, the supplement is presented as a theoretical text rather than in a question-and-answer format. The book asserts that Western astronomy originated from China's Canopy-Heaven model (gaitian) and that the foundation of the Zhoubi suanjing was based on a spherical earth model, not a flat earth model. Mei details how the Spherical Model (huntian 渾天) evolved from the Canopy Model and explains the reasons why different regions and countries adopt varying calendrical systems. He discusses the origin of the zodiacal houses and the rationale behind their permanence, while also connecting sidereal years and lunar days to human customs such as the Ramadan period. Mei differentiates between fixed solar terms (dingqi 定氣) and mean solar terms (hengqi 恒氣), investigates the relationship between the orientation of the Big Dipper and lunar phases, and explores the historical importance of the official declaration of the new moon (banshuo 頒朔) in ancient China. Furthermore, Mei critiques the superstitions and prohibitions that arose concerning calendar formulation and advocates for calendar reform that prioritises significant corrections, contending that minor discrepancies in seconds or fractions should not be exaggerated.

Mei Wending’s ability to explain these complex topics in an accessible and well-reasoned manner showcases his deep understanding. Many scholars regard him as the true bridge between Chinese and Western astronomy and calendrical sciences, and this work is a testament to that reputation. Apart from in the above-mentioned series, the supplement is integrated into the series Yihai zhuchen 藝海珠塵 and Congshu jicheng chubian 叢書集成初編.