Astronomy and Chen Zhixu’s Neidan Theory

Abstract

Chen Zhixu (陳致虛), a prominent Taoist master of the Yuan Dynasty, significantly contributed to aspects such as the creation of Taoist genealogy and the theoretical interpretation of Neidan (内丹 internal alchemy studies). Astronomy of different aspects served as an important intellectual resource for him. Chen Zhixu not only explained the correlative cosmological model in traditional internal alchemy theories, but also introduced systematic calendrical knowledge to broaden the astronomical foundation of his theoretical propositions, thereby strengthening the connection between internal alchemy practices and astronomical research. The model of the cosmic structure based on the Hun Tian theory (渾天說 the Spherical Heaven Theory, a major ancient Chinese cosmological theory that regards the sky as a sphere and encloses the earth in it) that he constructed is not merely a correlative illustration but also laid a solid mathematical foundation for his theoretical system. Nonetheless, Chen Zhixu’s methodological exposition of the hierarchy between internal alchemy practices and astronomical research reveals that his application of astronomical knowledge was selective and ultimately subordinated to, and constrained by, his Taoist transcendental goals. Therefore, Chen Zhixu’s work, to some extent, reveals a structured relationship between Taoism cultivation practices and ancient Chinese science.

1. Introduction

In the history of Taoist internal alchemy studies, Chen Zhixu 陳致虛 [1290–1343?; zi 字 Guanwu 觀吾; hao 號 Shang Yangzi (上陽子 Highest Yang Master)] was a representative figure. His model of correlative cosmology in cultivation practice not only inherited the existing sanctified classical astronomical knowledge (such as lunar phases and solar terms) and the method of analogy in previous internal alchemy studies, but also absorbed the new astronomical knowledge and specific calendar calculation data of his time, so as to enhance the correlative cosmological symbolism model of Taoist classics such as Zhouyi Cantong qi (周易參同契 Token for the Agreement of the Three According to the Book of Changes). Of particular importance was Zhixu’s use of astronomy, which provided a mathematical–cosmological rationale for internal alchemy, thus consolidating its cosmological foundation. Chen Zhixu’s work expanded the theoretical interface between the integration and absorption of astronomy into internal alchemy cultivation, further reinforcing the connection between internal alchemy theory and astronomy. This theoretical contribution deserves in-depth research.

Chen was a Taoist figure who lived in the Jiangxi (江西) region (a province in Southeast China) during the Yuan Dynasty. He was a key practitioner in the integration of the Southern Branch of the Golden Elixir (金丹派南宗 Jindanpai Nanzong) and the Quanzhen Dao (全真道 the School of Completion of Authenticity) in the Yuan Dynasty1. Chen Zhixu’s major Daoist texts consist of four titles: Jindan Dayao (金丹大要 Great Essentials of the Golden Elixir), Taishang Dongxuan Lingbao Wuliang Duren Shangpin Miaojing zhu (太上洞玄靈寶無量度人上品妙經注 Commentary to the Wondrous Scripture of the Upper Chapters of the Numinous Treasure on Limitless Salvation), Wuzhen Pian Sanzhu (悟真篇三注 Three Commentaries on Folios on Awakening to Perfection; this work incorporated Chen Zhixu’s commentary to Wuzhen Pian), and Zhouyi Cantong qi Fenzhang zhu (周易參同契分章注 Chaptered Commentary on Token for the Agreement of the Three According to the Book of Changes)2. Furthermore, Chen was a disciple of Zhao Youqin 趙友欽 (1270?–1340?, a Yuan Dynasty Taoist scholar who was proficient in astronomy, mathematics, and internal alchemy practice and had a formative influence on Chen Zhixu’s work). Zhao Youqin’s astronomical work, Gexiang Xinshu (革象新書 New Book on Reforming Observations of Celestial Phenomena), is a text that systematically synthesizes traditional Chinese calendrical and mathematical knowledge (J. Chen 2013, pp. 438–42). Against this backdrop, Chen Zhixu developed a solid foundation of knowledge of ancient Chinese astronomy, and the astronomical knowledge cited in his internal alchemy theory was primarily derived from Gexiang Xinshu.

A growing body of research, including Chinese and non-Chinese-language studies, has been conducted on Chen Zhixu. Zhou Ye (Zhou 2007), Wm Clarke Hudson (Hudson 2008), and He Jianming (J. He 2011) have explored Chen Zhixu’s life, works, and specific theoretical propositions, focusing on how he constructed his Taoist transmission lineage and expounded his doctrinal propositions. Zeng Chuanhui (Zeng 2004) analyzed Chen Zhixu’s theory of Cantong studies and Yijing studies 易學. Zhang Zehong primarily focused on the religious influence of Chen Zhixu in the Tusi (土司 chieftain) society in Southwest China (Z. Zhang 2015). Despite their valuable contributions, these studies have overlooked the astronomical dimension in Chen Zhixu’s internal alchemy theory. Only Yang Zilu and Yang Yuhui have acknowledged that Chen Zhixu’s work is grounded in a solid background of mathematical astronomy (Yang and Yang 2014); yet their exposition remains relatively brief, failing to elaborate on how Chen Zhixu integrated astronomical knowledge into the construction of his internal alchemy theory.

The primary study providing a detailed analysis of the astronomical knowledge in Chen Zhixu’s works is Alexei Volkov’s research (Volkov 2004). Volkov points out that Chen Zhixu’s citations and preservation of numerous contents from Gexiang Xinshu in his Durenjing zhu became an important basis for later scholars editing the Gexiang Xinshu. This demonstrates that Chen Zhixu must have been proficient in the astronomy of his time. Furthermore, it indicates that mathematical and astronomical knowledge during that period was disseminated, at least to some extent, through Taoist networks and was not confined solely to official institutions (Volkov 2004, p. 531). Diverging from this, the present study attempts to elucidate from a more specialized perspective of how Chen Zhixu’s application of astronomy is not merely a refinement of “correlative illustration”, it will argue that by providing a mathematical–cosmological rationale and wider using of empirical astronomical knowledge, Chen consolidated the epistemic foundation of internal alchemy. Meanwhile, it also reveals the limitations and boundaries of this application.3

2. The Origins and Development of the Tradition of Taoist Internal Alchemy Cosmology

The tradition of Taoist internal alchemy cosmology serves as one of the significant manifestations of ancient China’s core correlative cosmological thinking. In traditional Chinese religious and political philosophy, the cosmos is conceived as an organic whole in which all entities are bound by intrinsic patterns of correlative resonance. Astronomical phenomena are key manifestations of cosmic order, with specific astronomical phenomena corresponding to various changes in the human realm—which serves to reveal the basic structure, operational laws, and physiological trends of society and the human body. For emperors and Confucian scholars, celestial phenomena foreshadowed the rise and fall of dynasties; they were also of significant value for understanding earthly ethics and morality. In Taoism, for example, celestial phenomena manifested as Qirang 祈穰 and Cunsi 存思4, as well as models and alchemical fire times (火候 Huohou, referring to the timing of internal alchemy cultivation) in alchemical cultivation, whether in Waidan (外丹: external alchemy, which fabricates elixirs of immortality through the laboratory manipulation of minerals and metals) or internal alchemy [which is dedicated to refining and nurturing the inner essence, pneuma, and spirit (精氣神 Jing, Qi, Shen, the fundamental elements of internal alchemy practice within the human body)]. While different social groups conceptualize Heaven–human interaction in diverse ways, they consistently treat celestial phenomena as important sacred symbols. These perceptions, together with their associated ritual and belief practices, all form subsystems within the traditional Chinese religious tradition (H. Zhang 2021, p. 39).

The tradition of correlative cosmology in Taoist cultivation practices can be traced back to classical texts, particularly Zhouyi Cantong qi, which is praised as the “King of Alchemical Texts for All Ages 萬古丹經王”. It draws on Han Dynasty Yijing theories such as Najia (納甲 the association of trigrams with Heavenly Stems), Shi’er Xiaoxi Gua (十二消息卦: the Twelve Hexagrams of the Waxing and Waning Yin-Yang), and Guaqi Theory (卦氣說), the correspondence of hexagrams with seasonal pneuma. All the aforementioned theories are significant doctrines of Han Dynasty and laid a crucial foundation for the image-number tradition of Yijing studies (象數易學), which combines the Yijing schema with digital mysticism, Zhouyi Cantong qi elaborates on the operating laws of celestial bodies, and incorporates these astronomical elements to illustrate the principles governing the advancement and retreat of alchemical fire times in cultivation practice,5 thereby establishing the fundamental cosmological framework and Heaven–human correspondence for alchemical cultivation. As the text states, “Abide in the Center to control the outside: the numbers are found in the system of the pitch-pipes and the calendar (Lüli 律曆 temperament and calendar, a traditional Chinese system integrating music, astronomy, and mathematics)… Celestial tokens advance and recede; bending and stretching respond to the time (處中以制外, 數在律曆紀…天符有進退, 屈伸以應時 Pregadio 2012, pp. 69–70)”.

Later developments of internal alchemy theories and practice inherited and developed this theoretical approach of Zhouyi Cantong qi. Wuzhen Pian by Zhang Boduan 張伯端 of the Northern Song Dynasty. This is a significant work marking the integration of the Taoist alchemical cultivation model between external alchemy and internal alchemy; it also employs Yijing symbols and celestial phenomena as parallels to elaborate on the alchemical fire times for human cultivation. This is evident in verses such as “Between south and north, the ancestral source causes the hexagrams to revolve; from daybreak to dusk, the fire times accord with the Celestial Axis. 南北宗源翻卦象, 晨昏火候合天樞”, “When the sky clears, the moon shows half-bright; Already heard are the dragon’s roar and tiger’s cry 月才天霽半輪明, 早有龍吟虎嘯聲”, and “Heaven and Earth wax and wane in their own time; Only by discerning Yin-Yang’s ebb and flow can one grasp the Ji (機 the hidden key, omen, or pivotal moment of change in things) 天地盈虛自有時, 審能消息始知機” (Wuzhenpian Qianjie, pp. 8, 57, 92; Pregadio 2009, p. 35) all reflect the inherited correlative thinking of Zhouyi Cantong qi, correlating lunar phases and solar terms with the alchemical fire times, thereby constructing the fundamental theoretical framework for the internal alchemy cultivation model. Chen Zhixu’s annotations and commentaries on Wuzhen Pian and Zhouyi Cantong qi also demonstrate his inheritance of this tradition. (See Figure 1)

3. The Astronomical Foundation of Chen Zhixu’s Internal Alchemy Theory

On the basis of inheriting the tradition of Taoist internal alchemy cosmology, Chen Zhixu’s application of astronomical knowledge should be categorized into three distinct aspects according to the nature of the knowledge: the elucidation of general heaven-human correspondences, the broader use of empirical astronomical knowledge, and the construction of the metaphysical cosmic structure. First, the basic framework of Chen Zhixu’s internal alchemy theory is still based on the correlative cosmological model of traditional internal alchemy teachings; yet, his presentation is more detailed and clearer, refining the comparative and symbolic systems of cosmology for cultivation practice, making breakthroughs in overcoming the mystery and ambiguity in previous internal alchemy literature. Second, through the integration of the organized, empirical knowledge of astronomy, Chen Zhixu deepened and broadened the correspondence between alchemical fire times in internal alchemy cultivation and celestial phenomena. Finally, the Hun Tian mathematical cosmological model that he constructed integrates the “Heaven-Earth Numbers” (天地之數 Tiandi zhi Shu), a core numerical concept in image-number Yijing studies, where the calculated values derive from mathematical astronomy research. Thereby, a relatively rational and solid metaphysical cosmological structure was established for his theoretical system. Nonetheless, it must be clearly understood that Chen Zhixu’s use of astronomical knowledge was circumscribed by and ultimately subordinate to his goal of religious transcendence.

3.1. The Cosmological Symbolism in Chen Zhixu’s Internal Alchemy Theory

Chen Zhixu inherited the fundamental principles of the cosmic symbolic system from the traditional internal alchemy theory, while providing detailed explanations on the specific correspondences between the alchemical fire times of bodily cultivation and astronomical–calendrical phenomena. This constitutes a relatively conservative aspect of his use of astronomy.

In terms of its basic principles, Chen Zhixu articulates the triadic unity relationship among heaven, humanity, and Yijing in internal alchemy cultivation, laying the theoretical foundation for his correlative cosmology model. For Chen, whether it is the movement of the Sun, Moon, and stars, the mutual interaction and transformation of the Yin and Yang lines (陰爻 陽爻 Yinyao and Yangyao—two basic constituent units of hexagrams, where Yinyao symbolizes femininity, and Yangyao symbolizes masculinity), or the alchemical fire times in human cultivation, they all share the same essence—they are manifestations of the fundamental law of Yin and Yang governing the universe at different levels6. Building on Ge Zhaoguang’s systematization of correlative thinking, in Chen Zhixu’s theoretical framework, Heaven, Earth, other myriad things, and humanity are “of the same origin (同源 Tongyuan), of the same structure (同構 Tonggou), and of mutual responsiveness (互感 Hugan) (Ge 2008, pp. 105–6).” First, Chen Zhixu maintains that Heaven, Earth, and humanity are “of the same origin”—they are all derived from “the Dao”, while also embodying it: “For the Dao, it gives birth to Heaven; it gives birth to Earth; it facilitates the attainment of immortality and Buddhahood; it classifies and shapes all things 夫道也, 生天也, 生地也, 成仙佛也, 類萬物也.” (Jindao Dayao, p. 51). Second, since both the structure and operation of Heaven and Earth and that of the human body embody the same “Dao”, they are therefore “of the same structure”, sharing corresponding structural principles and operational laws: “the sun and moon in Heaven alternately pass through the crescent, quarter, and full moon phases, and alternately transition between the dark moon (晦 Hui, the end of the lunar month) and the new moon (朔 Shuo, the start of the lunar month); similarly, the Yin and Yang within the human body alternately return to the Taiji (太极 the Supreme Ultimate, a concept of perfection as opposed to ever-changing states) state and alternately shift into ever-changing states 譬如天上之日月, 忽忽而弦望, 忽忽而晦朔; 即如人身之陰陽, 忽忽而太極, 忽忽而無常” (Zhouyi Cantong qi Fenzhang zhu, p. 224): “Accomplished practitioners of cultivation analogize Heaven and Earth to their own bodies大修行人以天地而比一身” (Taishang Dongxuan Lingbao Wuliang Duren Shangpin Miaojing zhu, p. 429). Therefore, by examining the specific configuration of Heaven and Earth, one can unveil the internal bodily structure of the human body: “The Dao gives birth to all things; Heaven and Earth are the greatest among all things, and humans are the most intelligent among all things. If we seek from the Dao, humans are analogous to Heaven and Earth: the heart is analogous to Heaven, the kidneys to Earth, the liver corresponds to Yang, and the lungs correspond to Yin. From the upper to the lower, by observing the heavens above and examining the earth below, we can probe into the underlying mechanisms of the Dao; from the beginning to the end, by numerical calculations (e.g., astronomical degrees and calendrical computations), we can grasp the underlying principles of the Dao 道生萬物, 天地乃物中之大者, 人為物中之靈者. 別求於道, 人同天地, 心比天, 腎比地, 肝為陽, 肺為陰, 一上一下, 仰觀俯察, 可以賾其機; 一始一終, 度數籌筭, 可以得其理.” (Taishang Dongxuan Lingbao Wuliang Duren Shangpin Miaojing zhu, p. 426). Finally, since humans, Heaven, and Earth share the same origin and corresponding structure, there exists a relationship of “mutual responsiveness”; therefore, it is essential to “observe astronomical phenomena to perceive changes in temporal rhythms 观乎天文以察时变 (Taishang Dongxuan Lingbao Wuliang Duren Shangpin Miaojing zhu, vol. 2, p. 431)”, and dynamically adjust the alchemical fire times in internal alchemy cultivation based on guidance from astronomical phenomena.

In Jindan Dayao, Chen Zhixu outlines the specific progression of internal alchemy cultivation into seven stages: “Regulating Alchemical Fire and Following Omen-Signs (符 Fu, the auspicious signs and fire times nodes in cultivation) (行火進符 Xinghuo Jinfu)”, “the Dark Moon, New Moon, Quarter Moons, and Full moon (in Lunar Phases) (晦朔弦望 Huishuo Xianwang)”, “Guarding Against Perils and Preserving Vitality (防危護失 Fangwei Hushi)”, “Punishment and Virtue Aligning with Mao-You (卯酉刑德 Maoyou Xingde)”, “Ceasing Alchemical Fire and Purifying Thoughts (沐浴滌慮 Muyu Dilü)”, “Generation and Extinction with Hexagram Lines and Zhu (銖 an ancient Chinese weight unit, adopted in internal alchemy to measure subtle alchemical fire times) for Alchemical fire times 生殺爻銖 (Shengsha Zhuyao)” and “Shedding the Mortal Frame and Transforming the Alchemical Cauldron (脫胎換鼎 Tuotai Huanding)”. Each stage entails distinct cultivation objectives and key things to note. Among these, the first three stages serve as a general overview of the entire internal alchemy cultivation process, focusing on the initial stage of the cultivation. The subsequent three stages elaborate on the stable progression in the middle phase. The final stage, “Shedding the Mortal Frame and Transforming the Alchemical Cauldron”, represents the consummate state after the completion of internal alchemy cultivation. Each stage corresponds to specific solar terms, lunar phases, Shi (時 the ancient Chinese two-hour time unit), and hexagrams, forming a nested interconnected structure that unifies the macrocosm and microcosm. The following sections provide a detailed analysis of each stage in sequential order.

“Regulating Alchemical Fire and Following Omen-signs” refers to the start of cultivation practice, corresponding to the Zi Shi (子時 23:00–01:00) on the first day of the lunar month. At this time, the Sun and Moon are in conjunction, and Yang pneuma 陽氣 begins to stir. This moment also corresponds to the Fu Gua (复卦 the Return Hexagram䷗), which consists of five Yin lines and one Yang line—with the Yang lines situated at the initial position (初位 Chuwei, the bottom-most line among the six lines), representing the initial stirring of Yang pneuma. “The Dark Moon, New Moon, Quarter Moons, and Full moon” stage focuses on explaining the initial phase of cultivation practice, corresponding to the period from the solar–lunar conjunction at Zi Shi on the first day to “the moon rising at the Geng (庚 referring to west) position 月現庚上” on the third day of the lunar month—a time when the moon’s light first appears. This period corresponds to the Zhen Gua (震卦 the Quake Hexagram䷲); at this moment, “Yang pneuma begins to rise and spread, and Sha (砂 cinnabar Yang-symbolic essence) and Gong (汞 mercury Yin-symbolic essence) lay the foundation 陽氣初布, 砂汞立基”—making it the perfect time to begin gathering and blending the medicinal ingredients (referring to essence, pneuma, and spirit in internal alchemy terminology). “Guarding Against Perils and Preserving Vitality” describes a state of caution and resolute dedication to one’s will during the initial stage of gathering the medicinal substances: “For this is a time when one must seal and secure the Three Treasures (essence, pneuma, and spirit); one should only focus wholeheartedly. Otherwise, there will be consequences of losing one’s life 蓋是時也, 閉塞三寶, 唯當專心致志, 否則有喪身失命之事.” (Jindan Dayao, pp. 26–7).

The stage known as “Punishment and Virtue Aligning with Mao-You” refers to the relatively stable middle phase in internal alchemy cultivation, and is of the utmost importance throughout the entire process. This stage corresponds to six lunar mansions(星宿 Xingxiu a method of distinguishing celestial regions) on the celestial sphere: Di (氐 the Root Mansion), Fang (房 the Room Mansion), Xin (心 the Heart Mansion), Wei (胃 the Stomach Mansion), Mao (昴 the Hairy Head Mansion), and Bi (畢 the Net Mansion): these lunar mansions fall under the Mao-You Fenye (卯酉分野 the celestial regions corresponding to the eastern and western directions) in the twelve Ci (次 is also an ancient Chinese astronomical zoning system that divides the ecliptic into 12 segments). It also aligns with the daily Mao Shi (卯時 dawn) and You Shi (酉時 dusk), the seasonal Spring Equinox in the Mao month (卯月 the second lunar month) and the Autumn Equinox in the You month (酉月 the eighth lunar month)—these two equinoxes signify periods of alternating cold and heat, the 8th and 23rd days of the lunar calendar (the waxing quarter moon 上弦月 and waning quarter moon 下弦月, when the Moon is half-illuminated and half-darkened—on the 8th, the Moon reaches the celestial meridian 天中 at Mao Shi; on the 23rd, it reaches the celestial meridian at You Shi), and the hexagrams Li Gua (離卦 the Fire Hexagram䷝, with four Yang lines and two Yin lines, corresponding to Mao Shi) and Kan Gua (坎卦 the Water Hexagram䷜, with four Yin lines and two Yang lines, corresponding to You Shi). Together, these form a comprehensive nested cosmic rhythm: “There is the Mao-You of Heaven and Earth, the Mao-You of a year, the Mao-You of a month, the Mao-You of a day, and the Mao-You of a Shi 有天地之卯酉, 有一年之卯酉, 有一月之卯酉, 有一日之卯酉, 有一時之卯酉.” (Jindan Dayao, p. 27). At this stage, the Yin pneuma and Yang pneuma in the cosmos are in a delicate state of balance; these two pneuma are on the cusp of substantial transformations, while their original balanced state still retains residual momentum. Analogously applied to the human body, this cosmic state corresponds to a pivotal critical juncture in internal alchemy cultivation, where “Yin and Yang are in equal proportion 陰陽相半.” At this phase, practitioners should let go of discursive thoughts and focus wholeheartedly on safeguarding the mind—only then can they navigate this critical juncture. Otherwise, all previous cultivation efforts will come to naught:

“In the Mao month, there are four Yang lines and two Yin lines, the dominance of Yin is about to depart (Yin’s influence is waning), and since Yin presides over destruction, although the two Yin lines in Mao are no longer capable of overcoming Yang, their destructive force has not yet dissipated—hence it is termed punishment. In the You month, there are four Yin lines and two Yang lines. The dominance of Yang is about to depart (Yang’s influence is receding), and since Yang presides over creation, although the two Yang lines in You cannot overcome Yin, their life-force persists—hence it is termed virtue.”

卯月乃四陽而二陰, 陰道將離, 而陰主殺, 是以卯之二陰, 陰已不能勝陽, 然殺氣未絕, 故為刑也. 酉乃四陰而二陽, 陽道將離, 而陽主發生, 是以酉之二陽, 陽雖不能勝陰, 然生意尚存, 故為德也.

(Jindan Dayao, p. 29)

“Ceasing Alchemical Fire and Purifying Thoughts “refers to a state when Yin and Yang are in a true state of balance (with three Yin lines and three Yang lines), corresponding to the Tai Gua (泰卦 the Interacting Peace Hexagram䷊, representing the harmonious interaction of Yin and Yang). Since “this moment is close to the Mao and You Shi 其時則近卯酉”, practitioners must still refrain from active manipulation of alchemical fire and forcing progression—actions that would agitate Spirit-Mind (心神 Xinshen). Instead, they should continue to refine the body and mind, letting go of all worldly attachments to enable the natural interaction and unification of Yin and Yang pneuma:

“Muyu (沐浴 Bathing, referring to a pivotal process of purification, balance, and refinement in cultivation) occurs precisely when Yin and Yang are in equal proportion, and the energies of Qian (鉛 lead, another Yang-symbolic essence) and Gong are in a state of stagnant stability… It demands that one’s body be like withered wood and one’s mind like dead ashes—this is precisely what is referred to as muyu.”

沐浴者, 適當陰陽相半, 鉛汞氣停…直要形如槁木, 心若死灰, 是謂之沐浴也.

(Jindan Dayao, p. 29)

The core principle of “Generation and Extinction with Hexagram Lines and Zhu” remains consistent with that of “Ceasing Alchemical Fire and Purifying Thoughts.” It emphasizes that in the later phase of internal alchemy cultivation, practitioners must eradicate “Xin Zhong Zei (心中賊 inner thieves—a metaphorical expression of miscellaneous thoughts in mind)”, namely, distracting thoughts, delusions, and selfish desires that will hinder cultivation, in anticipation of the perfection of alchemical fire times when “the count and rhythm of Yin and Yang are fulfilled 陰陽之數既足.” Finally, “Shedding the Mortal Frame and Transforming the Alchemical Cauldron” showcases the ultimate state of perfection and fruition upon the successful completion of internal alchemy cultivation. This state is analogous to the conclusion of the traditional twenty-four Chinese solar terms and the final stage of gestation when a woman’s ten-month pregnancy nears its end:

“When the solar terms have completed a full cycle, (the practitioner) sheds the mortal frame and achieves divine transformation… When the elixir matures, the sacred embryo (聖胎 Shengtai a metaphorical symbol refined from golden elixir) is fully formed, and the sacred infant (嬰兒 Ying’er) is accomplished—thus becoming a Zhenren (真人 a transcendent being).”

節氣既周, 脫胎神化…直至丹熟胎完, 嬰兒成就而成真人.

(Jindan Dayao, p. 29)

From Chen Zhixu’s perspective, internal alchemy should be a method of self-cultivation accessible to as many believers as possible and inherently possess clear, unambiguous, practical, and actionable guidelines that practitioners can strictly follow:

“I compiled this Jindan Dayao. Within it, defying taboos, I offers detailed elaborations—unfolding and clarifying systematic explanations that directly open doors and pave the way for later practitioners seeking immortality.”

作此《金丹大要》. 其中冒禁詳述, 開顯條說, 直與後來學仙之士, 辟門引路.

(Jindan Dayao, p. 3)

However, texts composed prior to the work of Chen Zhixu often employed a large number of esoteric metaphors when explaining the practice—deliberately obscuring the practical content and leaving practitioners at a loss as to how to begin:

“Thousands of scrolls and chapters, whether lengthy odes or short verses, are nothing but constructed illusory images and symbolic forms—using one thing to metaphorize another. What difference is there between this and “discussing emptiness within emptiness itself” or “recounting dreams while still in a dream”? If one seeks their practical effects, it is as vague and futile as chasing the wind… These works are muddled and disordered, rambling and fragmented… They mislead later practitioners, and the confusion they cause grows all the more severe.”

千篇萬卷, 長歌短句, 無非假像設形, 借彼喻此, 何異空底談空, 夢中說夢, 求其功效, 茫如捕風…顛倒錯亂, 枝蔓條折…迷誤後人, 惑也滋甚.

(cited from Jindan Zhengzong (金丹正宗 Golden Elixir: The Orthodox Tradition, an internal alchemy text compiled approximately during the Song and Yuan Dynasties, which criticizes the abuse of metaphors in previous internal alchemy works. Jindan Zhengzong, p. 188)

This situation reflects the profound contradictions inherent in the internal alchemy theory, as a religious practice tradition that embodies the triple qualities of technicality, mysticism, and transcendence. However, Chen Zhixu’s expositions not only synthesize and explicate the triadic unity relationship of Heaven, humanity, and Yijing in internal alchemy cultivation, but also construct a concrete cultivation model that corresponds precisely to natural rhythms. The natural phenomena and rhythms involve such elements as solar terms, lunar phases, time periods (Shi), lunar mansions, directions, and women’s gestation. This model, to a certain extent, bridges the contradiction in traditional internal alchemy theories.

3.2. The Empirical Astronomical Knowledge in Chen Zhixu’s Internal Alchemy Theory

Chen Zhixu also incorporated the specific astronomical knowledge of his time into his own theoretical system. His work enhanced and further elucidated the scientific implications of the Taoist classics Lingbao Duren Jing and Zhouyi Cantong qi, which he annotated—and, more significantly, provided a more profound and concrete argument for how celestial phenomena can guide and influence the alchemical fire times in cultivation practices. In this regard, Chen Zhixu demonstrated his mastery of empirical astronomy and its unique application within his internal alchemy theory.

Take the line “The sun, the moon, and the five planets also undergo waxing and waning 日月五星, 亦有盈虧” from Lingbao Duren Jing as an example. Interpreted through a conventional literal lens, this line typically denotes astronomical phenomena such as solar and lunar eclipses, lunar phase changes, and the invisibility and visibility of the five classical planets (Jupiter 木, Mars 火, Saturn 土, Venus 金, and Mercury 水), among others. Chen Zhixu, however, pointed out that this line “refers not only to solar and lunar eclipses as instances of waxing and waning 非但指日月晦食為虧盈”; it also encompasses phenomena in calendrical calculations such as intercalary months 閏月, axial precession7 歲差, and large/small months 大小月—phenomena characterized by “the irregularity in the division of degrees 分度不齊,” (Taishang Dongxuan Lingbao Wuliang Duren Shangpin Miaojing zhu, p. 428)—that is to say, calendrically relevant celestial cycles with no common divisor. Therefore, from Chen Zhixu’s perspective, beyond solar and lunar eclipses and lunar phases, other celestial and calendrical phenomena also serve as important reference points for internal alchemy cultivation.

Furthermore, in his annotations on Zhouyi Cantong qi, Chen Zhixu offered a more detailed analysis of the impact of axial precession on internal alchemy cultivation practice. He implied that the positions of the conjunctions of the Sun and the five classical planets are related not only to months and directions, but also to the phenomenon of axial precession. As a result of axial precession, the stellar background of the conjunctions of the Sun with the five classical planets—which embody the interaction between Yang pneuma and the Five Elements 五行 and thus may not only affect the Sun’s luminosity but also provide insights for the selection of fire times in internal alchemy cultivation—shifts gradually over time. In addition, given the corresponding relationship between the lunar mansions (in the stellar background) and the human body, it is essential to attend to the positions of these conjunctions relative to the lunar mansions:

“alchemy cultivation is closely tied to cosmic creation and evolution, thus making it more difficult than governing a state. Furthermore, it uses lunar mansions to analogize the human body. As for the phrase “The sun unites with the essence of the Five Elements 日合五行精”: During the Zi, Chou, and Yin months 子, 丑, 寅月, the Sun conjoins with the Five Classical Planets in the northern celestial direction… In the period of Emperor Yao 堯, the “celestial center (the celestial reference point)” was set at Zi 子 position (north); on the winter solstice of the Jiachen 甲辰 year, the Sun resided at the Xushu (虛鼠 Void Rat) Mansion; during the Taichu 太初 era of the Han Dynasty (104 BCE–88 BCE), the Sun was at Qianniu Mansion (牽牛 Ox Herd) on the winter solstice; during the Taiyan calendar (太衍历 compiled by the Buddhist monk Yi Xing 一行 and officially adopted in 727 CE) era, the Sun was at Dongdou Mansion (東鬥 Eastern Dipper); and from the Song Dynasty to the present, the Sun has been at Nanji Mansion (南箕 Southern Winnow) on the winter solstice. This is what is referred to as axial precession. Thus, when the Sun aligns with the Fire火 and the Earth 土 (two of the Five Elements 五行, corresponding to Mars and Saturn), its luminosity is enhanced; when it aligns with the Metal 金 and the Water 水 (the other two, corresponding to Venus and Mercury), its radiance becomes even more brilliant.”

修丹一事, 紧关造化, 故比御政为难. 复以星宿喻身. 日合五行精者, 子, 丑, 寅月, 日合五星於北…堯時天心建子, 甲辰冬至, 日次虛鼠；漢太初冬至, 日次牽牛; 唐太衍冬至, 日次東鬥; 宋至今冬至, 日次南箕. 此謂歲差. 故太陽得火, 土益精光; 得金, 水愈炫彩.

(Zhouyi Cantong qi Fenzhang zhu, p. 229)

Chen Zhixu also employed the astronomical insights of Zhao Youqin, his master, to further develop his theoretical propositions. Take the line “Between Hui and Shuo, (the sun and moon) align in accordance with the cosmic tally and abide by the cosmic Mean, 晦朔之間, 合符行中” from Zhouyi Cantong qi. This line’s essential intent is to associate Hui and Shuo in the incipient stage of internal alchemy cultivation. Furthermore, based on Zhao Youqin’s perspective that “the sun is above the moon 日在月上”8, Chen Zhixu observed that during Hui and Shuo, not only do the Sun and Moon converge, but the Sun is also positioned above the Moon. Moreover, since the Sun belongs to Yang and represents masculine qualities, while the Moon belongs to Yin and represents feminine qualities, this state is analogous to “the union of a man and a woman—with the man above and the woman below, where the woman is covered by the man and thus invisible 男女交合, 男在上, 女在下, 女为男覆而不可见” (Zhouyi Cantong qi Fenzhang zhu, p. 249). This symbolic interpretation also explains the absence of visible moonlight during these phases. Moreover, since the moonlight derives from the Sun, the absence of moonlight alongside the conjunction of the Sun and Moon indicates that though the celestial state (at Hui and Shuo), which is in pure Yin at this time, Yang pneuma is about to emerge—this “can be compared to the state of Shaoyin (少陰 minor Yin) in human physiology 比人間之少陰也”. Therefore, by taking this twelve-fold annual alignment as a reference to calibrate the rhythms of internal alchemy cultivation, practitioners can precisely attune to the fire times governing the cyclical waxing and waning of Yin and Yang:

“In the heavens, Taiyin (太陰 the moon) has twelve celestial degrees, during which it forms a conjunction with the sun; in human physiology, Shaoyin also has twelve (corresponding) degrees, guiding practitioners to practice in secrecy while studying the scriptures (Zhouyi Cantong qi). This is the proper and fundamental order of Yin and Yang.”

天上太陰有十二度, 與太陽合壁, 人間少陰有十二度, 以隱行看經, 此陰陽之正也.

(Zhouyi Cantong qi Fenzhang zhu, p. 249)

This exposition takes Zhao Youqin’s theoretical viewpoints as a thread and links the relationship between men and women (as a symbol of Yin–Yang interaction), the conjunction of the Sun and the Moon, and the internal alchemy alchemical fire times in the human body. It explains why the Moon appears dark on the first day of each lunar month yet heralds the onset of Yang pneuma: “The moon is of pure Yin. If it does not receive the Yang pneuma from the sun, how can it wane and wax again? 夫月純陰也, 不感日之陽氣, 安能滅而復生?”(Jindao Dayao, p. 27).

In his commentary on the line from Zhouyi Cantong qi, “Among the suspended images that send forth their light, none is greater than the Sun and the Moon; Probe the Spirit to understand the transformations 懸象著明, 莫大乎日月, 窮神以知化 (Pregadio 2012, p. 137)”, Chen Zhixu also cited relevant discourses in Gexiang Xinshu. He pointed out that according to the cosmological structure of the Hun Tian theory, the earth is a flat plane, while the Heaven—enveloping the Earth as pneuma—rotates around it incessantly: “The way of Heaven rotates leftward, completing one full circuit each day, traversing over 550,000 li; the earth lies within this pneuma, remaining motionless like a floating board on water 天道左運, 一日一周遭, 行五十五萬餘里; 地在其炁之中, 如水上之浮板而不動 (Zhouyi Cantong qi Fenzhang zhu, p. 215; cited from Gexiang Xinshu, p. 224).” This includes the Sun, regarded as the “Primordial pneuma of Heaven and Earth 天地之元炁”, and the Moon, seen as the “Ultimate Essence of Heaven and Earth 天地之至精”:

“The celestial sphere has 365.25 degrees. Each day and night, the heaven complete one full cycle, which is considered one day. The sun moves one degree per day, and when it travels 30 degrees, it constitutes one month; the moon moves slightly more than 30 degrees per day, and when it completes a full cycle around the heaven, it is called one month. The sun moving one degree is referred to as one day.”

周天三百六十五度余四之一, 每昼夜, 天一周遭为一日. 太阳一日行一度, 行及三十度为一月; 太阴一日行三十度有奇, 月一周天, 谓之一月. 日行一度, 谓之一日.

(Zhouyi Cantong qi Fenzhang zhu, p. 215)

Thus, the Sun and Moon illuminate the Earth, enabling all things to rely on the Sun’s “fiery pneuma of Yang, scarlet and intense, to grow and bear fruit 陽火赫赤之氣以生長成實.” The moon, originally devoid of light—”its body entirely dark 其體全黑”—acquires its phases of waxing and waning by receiving sunlight: “The moon itself has neither fullness nor deficiency; its appearance depends solely on how much sunlight it receives 體本無圓缺, 在乎受日光之多少 (cited from Gexiang Xinshu, p. 245.” Hence, the moon symbolizes the ultimate Yin of Heaven and Earth, representing fertility and gestation: “through the transformative function of its watery Yin, it nurtures and fosters gestation 其陰水運化之功, 以孕產滋育.” This sublime and divine operational pattern illustrates that the Sun’s spirit is “inexhaustible and unfathomable 有不可得而窮極,” while the Moon’s “transformative principle (化 Hua)” contains “that which can never be fully revealed 有不可盡泄者.” Together, they symbolize the waxing and waning of Yin and Yang in the cosmos; the human journey of birth, aging, illness, and death; and even the possibility of reversing Yin and Yang through alchemical practice to achieve the Elixir. These constitute the essential “divine nature” and “transformative principle” within the universe:

“The celestial bodies of the sun and moon serve as models for Yin and Yang: Just as the sun and moon reside in heaven with their lunar phases and solar alignments, so do Yin and Yang exist in the world through alternating cycles of compliance and reversal, generation and completion (Shunni Shengcheng 順逆生成 Shun refers to the natural cycle of life, aging, sickness, and death, while Ni refers to reversing the forces of Yin and Yang to attain the Elixir). The sun embodies the pure pneuma of Yang, termed Great Yang 太陽; the moon embodies the pure essence of Yin, termed Great Yin太陰.”

法象日月以喻陰陽: 日月麗乎天而有朔望對合, 陰陽在乎世而有順逆生成. 日乃純陽之炁, 謂之太陽; 月乃純陰之精, 謂之太陰.

(Zhouyi Cantong qi Fenzhang zhu, p. 215)

Therefore, practitioners must thoroughly comprehend this principle in order to “exhaust their divinity to comprehend transformation”. In brief, Zhao Youqin’s exposition of the Hun Tian theory likewise served as the intellectual foundation for Chen Zhixu’s elaboration on the correspondence between celestial phenomena and cultivation practices of the human body.

Chen Zhixu also cited Zhao Youqin’s research on the phenomenon where the Moon still receives sunlight even when the Earth is positioned between it and the Sun. As he explains, “When the sun and moon stand opposite one other in the heavens and are separated by the Earth, the moon can still receive the sun’s light. This is because the Yin and Yang essential pneuma subtly connect despite obstacles, much like a magnet attracting iron or a bell responding to frost 日月對望, 為地所隔, 猶能受日之光者, 蓋陰陽精氣, 隔礙潛通, 如吸鐵之石, 感霜之鐘.” (Gexiang Xinshu, p. 245). In other words, there exists an inductive effect similar to a magnetic field between the Sun and Moon, and sunlight transmits across the Earth using this invisible “field” as a medium to reach the Moon. For his time, Zhao Youqin’s viewpoint represented a plausible hypothesis imbued with the characteristics of organicism and essentially concluded a universal law of the interaction between Yin and Yang. Therefore, this mechanism is not limited to the Sun and Moon; it can be extended to all scenarios of Yin–Yang mutual induction. Building on this view, Chen Zhixu went on to argue the feasibility of absorbing the essential Yin and Yang pneuma even from tens of thousands of li 里 away—during internal alchemy cultivation, and interpreted the invisible “field” as “Huang Po” (黃婆 a common esoteric term in internal alchemy practice, which generally refers to the Earth element among the Five Elements and serves as a mediator to harmonize Yin and Yang):

“Those who are ignorant may claim that when the sun and moon stand opposite each other, they are separated by the Earth. Little do they know of the vastness and height of the heavens, and the principle that the Yin and Yang pneuma can achieve subtle penetration despite obstacles.”

愚人或謂日月對望, 為地所隔. 彼豈知天之高遠, 而陰陽之炁, 有隔礙潛通之理.

(Zhouyi Cantong qi Fenzhang zhu, p. 226)

“These bodies (the Yin and Yang essential pneuma) are separated by as many as tens of thousands of li; yet if Huang Po acts as a go-between to facilitate their union, even the farthest distance becomes extremely close.”

二物間隔, 動幾萬里, 若得黃婆以媒合之, 則雖至遠而至近也.

(Zhouyi Cantong qi Fenzhang zhu, pp. 251–2)

In short, by drawing on Zhao Youqin’s new astronomical insights, Chen Zhixu further expanded the astronomical foundation of internal alchemy theories.

Furthermore, Chen Zhixu criticized kalpa and cosmic destiny thoughts (劫運 Jieyun, cosmic cycles in Buddhist–Daoist thought) of Lingbao Duren Jing. In his interpretations, he replaced the scripture’s other-power-dependent religious practice with self-power-dependent internal alchemy cultivation. As this scripture states, “The celestial and terrestrial cosmic cycles inevitably come to a period of decline and termination 天地運度, 亦有否終”. This passage emphasizes that surviving the periodic cosmic catastrophes (kalpa) requires one’s devotion to the Dao, and practicing rituals such as fasting, incense procession, and continuous recitation of this scripture. This aligns with Chen Zhixu’s interpretation:

“Through fasting in unison (with a shared devotion to the Dao), performing incense processions six times daily, and reciting the scripture ten times, blessings will descend immediately, dispelling all misfortunes.”

齊心修齋, 六時行香, 十遍轉經, 福德立降, 消諸不祥.

(Taishang Dongxuan Lingbao Wuliang Duren Shangpin Miaojing zhu, p. 427).

Therefore, this passage reflects a Messianic-like conception of kalpa, and also a core element of the practice model in Lingbao Duren Jing. Chen Zhixu, however, rejected this practice model. Instead, he cited Zhao Youqin’s research on polar days and polar nights to argue that the original meaning of this statement in Lingbao Duren Jing refers to the phenomenon of polar days and polar nights the far northern regions, where abnormal day–night phenomena occur. He reasoned that if the universe were ultimately to come to ruin, ordinary people would be unable to escape the kalpa through methods such as ritual ceremonies of prayer and supplication:

“In the Shuofang (朔方 the remote northern frontier of ancient China), dawn breaks before a cooked sheep’s shoulder blade is fully done; if one goes even farther, the rising and setting of the sun occur in an instant (cited from Gexiang Xinshu. p. 243). This is what is meant by the ‘operation of heaven and earth’, which also has its periods of decline and termination… If we literally assert that the heavens and earth will truly come to an end, how many people would survive? Who would be able to perform fasting rituals and incense processions? And who would be able to recite scriptures?”

朔方最遠之地煮羊胛未熟而天曉, 又遠則去日之出沒, 只在須臾。是為天地運度, 亦有否終…若直謂天地果然運終, 則民生其有幾何? 孰得而修齋行香, 又孰得而誦經乎?

(Taishang Dongxuan Lingbao Wuliang Duren Shangpin Miaojing zhu, pp. 427, 429)

Therefore, the scripture, in essence, reaffirms the referential role of astronomical phenomena for personal internal alchemy cultivation, “analogizing the cosmos to one’s own body 以天地而比一身” (Taishang Dongxuan Lingbao Wuliang Duren Shangpin Miaojing zhu, p. 427).

Furthermore, this assertion falls within the framework of his proposed distinction between “Daoyong” (道用, Application of the Dao) and “Shifa” (世法, Secular Method)—two divergent approaches to interpreting the scripture. This constitutes one of the central themes in his commentary. Specifically, “Shifa” refers to a literal, mundane understanding of the text, representing a practice focused on “diligent recitation and the pursuit of blessings 精勤誦念而求福.” In contrast, “Daoyong” signifies the correct, transcendent comprehension of the scripture’s true meaning, enabling one to “cultivate according to it and ascend to immortality 依之修行而登仙,” thereby embarking on the authentic path of the Golden Elixir. (Taishang Dongxuan Lingbao Wuliang Duren Shangpin Miaojing zhu, p. 394).”

For instance, the original text of Lingbao Duren Jing states, “After the scripture was recited eight times, women conceived, birds and beasts nurtured their embryos, and all beings—whether already born or yet unborn—all attained growth and completion 說經八遍, 婦人懷妊, 鳥獸含胎, 已生未生, 皆得生成.” On a literal level, this describes the miraculous efficacy of reciting the scripture. However, Chen Zhixu reinterpreted this passage allegorically, arguing that:

“These two approaches—Daoyong and Shifa—coexist. As for Shifa, it simply adheres to the literal meaning of the scripture, which needs no further elaboration here. Regarding Daoyong, for practitioners returning of the Golden Liquor to the Cinnabar Field (Jinye Huandan 金液還丹the process of elixir completion through nine cycles), if they have not yet obtained the Primordial pneuma (Xiantian Yiqi 先天一炁 the subtle breath upon which the human body relies to revert to its primordial origin), their entire body remains in a state of Yin. The empty space within the Li hexagram—is this not what is metaphorically called the woman? … ‘all attained growth and completion’ signifies that the embryo within the Golden Cauldron (Jinding 金鼎cultivation container, a metaphorical expression of the human body, borrowed from the external alchemy term) is fully formed and its pneuma is sufficient.”

此道用與世法兩存. 世法則依經云, 不又復贅. 道用則修金液還丹之士, 未得先天一炁, 則一身皆陰. 若離中虛, 豈不謂之婦人乎?…皆得生成者, 金鼎之胎完炁足.

(Taishang Dongxuan Lingbao Wuliang Duren Shangpin Miaojing zhu, pp. 396–7)

That is to say, as understood from the perspective of “Daoyong”, the scripture describes the process through which a practitioner—initially in a state of pure Yin before obtaining the primordial pneuma—achieves the nurturing of the spiritual embryo by means of correct practice.

In light of this, Chen Zhixu’s application of astronomical knowledge also served as an auxiliary tool to develop the connotations of “Shifa” and “Daoyong” and articulated his own system of cultivation practice as he interpreted the scripture.

It should be noted that Chen Zhixu’s critique of kalpa and cosmic destiny thought is informed by Zhao Youqin’s calendrical paradigm. Zhao Youqin criticized the nihilistic absurdity and lack of empirical verification of the Neo-Confucian Shao Yong’s 邵雍 Yuan-Hui-Yun-Shi theory9 元會運世說, a cosmological model that divides time into cyclical units, and argued that this theory “derives irregular cosmic processes from a rigid numerical system 以整齊之數推不齊之運” (Gexiang Xinshu, p. 235), thereby fundamentally rejecting the rationality of kalpa-like theories. Yet, by using Lingbao Duren Jing as a specific case, Chen Zhixu expanded the scope of application of Zhao Youqin’s viewpoint. He not only rejected the practice model of Lingbao Duren Jing, but also constructed additional classical grounding for the corresponding relationship between celestial movements and internal alchemy cultivation.

3.3. The Mathematical and Metaphysical Structure of the Universe in Chen Zhixu’s Internal Alchemy Theory

Chen Zhixu also integrated and reinterpreted the astronomical research of Zhao Youqin as well as other significant astronomical knowledge, constructing a mathematical and theoretical cosmic model based on the Hun Tian theory. Through this process of model building, he established a relatively rational metaphysical structure of the universe for his internal alchemy theory system. This represents the most groundbreaking and exploratory aspect of Chen Zhixu’s application of astronomical knowledge.

The cosmic model constructed by Zhao Youqin is analogous to the crystalline spheres system proposed by the ancient Greek astronomer Ptolemy. The Sun, Moon, and stars move along their distinct circular orbits. Among these celestial bodies, the Moon is closest to the Earth, the Sun occupies the middle position, and the Lunar mansions are farthest away from the Earth. Furthermore, because the apparent diameters of the Sun and the Moon are equal yet the Sun is farther from the Earth than the Moon, the actual volume of the Sun is larger than that of the Moon:

“The celestial sphere are round like pellets; the center of this spherical body is the focal point of the Liuhe (六合 literally ‘the target of the Six Directions’—referring to ‘up, down, east, west, north, south’).”

天體圓如彈丸, 圓體中心, 六合之的也.

“The Sun is close to the celestial sphere, while the Moon is far from it.”

日與天 (球) 相近, 月與天 (球) 相遠.

“The Sun’s spherical body is large, and the Moon’s is small.”日之圆体大, 月之圆体小.

(Gexiang Xinshu, pp. 235, 245, 246)

Chen Zhixu further developed Zhao Youqin’s aforementioned viewpoints in response to the needs of internal alchemy cultivation. Drawing from the classical astronomical treatise Sanwu Liji 三五曆紀 (a mysterious text from the Three Kingdoms period blending creation myths with astronomy), Chen Zhixu noted that the distance from the zenith to the Earth is 90,000 li, and the farthest point of the celestial sphere beneath the Earth is also 90,000 li from the Earth. Thus, the total vertical span of Heaven is 180,000 li (the sum of the two distances), because this data aligns with the theory of the correspondence between numbers and the cosmos in the tradition of image-number Yijing studies, which holds that “the Heaven numbers begin at one and end at nine”10:

“Sanwu Liji states… Numbers begin at one, take form at three, reach completion at five, flourish at seven, and attain their end at nine. Thus, the distance between Heaven and Earth is 90,000 li. From this, we know that the distance from Earth’s surface to Heaven is 90,000 li, and the distance from the Earth’s surface to the farthest point of Heaven beneath the Earth is also 90,000 li. Therefore, the total height of Heaven’s celestial sphere (i.e., from its highest point above Earth to its lowest point below Earth) is 180,000 li.”

三五曆紀曰…數起乎一, 立於三, 成於五, 盛於七, 處於九, 故天去地九萬里. 則知地上至天九萬里, 地下亦九萬里, 是天之體中高十八萬里.11

(Taishang Dongxuan Lingbao Wuliang Duren Shangpin Miaojing zhu, p. 426)

Chen Zhixu further cited data from Zhao Youqin that the diameter of the Earth is 150,000 li, and the east–west width of Heaven is also 150,000 li. Thus, the celestial sphere is elliptical in shape: “Since as the east–west width of the earth measures 150,000 li, it follows that Heaven has a total height of 180,000 li, thus the Hun Tian theory’s claim that ‘Heaven is shaped like a chicken’s egg (elliptical in shape)’ holds true 如地之寬闊…通十五萬里徑, 與十八萬里之高, 則渾天謂形如雞子 (橢圓) 者是矣12.” (Taishang Dongxuan Lingbao Wuliang Duren Shangpin Miaojing zhu, p. 426). Furthermore, Chen Zhixu provided other significant astronomical data, including that the diameter of the Sun measures “ 845 li with a slight excess 闊八百四十五里差餘”; the diameter of the Moon measures “670 li and a small fraction 闊六百七十里有奇”; the circumference of the celestial sphere measures “over 550,000 li 五十五萬餘里”; and the orbital circumference of the Sun measures “330,000 li… with each degree of the celestial sphere corresponding to 1390 li 計三十三萬里…天每度有一千三百九十里”. Finally, this included data showing that for the Moon, “each degree [of its orbit] corresponds to only 670 li, and when completing a full cycle of over 365 degrees, the total amounts to only 240,000 li 一度止得六百七十里, 週三百六十五度餘, 止計二十四萬里”. (Taishang Dongxuan Lingbao Wuliang Duren Shangpin Miaojing zhu, p. 428). Using these data, he proposed a relatively comprehensive mathematical cosmic model.

The data provided by Chen Zhixu are largely consistent with each other, and he also adopted the core framework of Zhao Youqin’s cosmic model—with only one key modification: he changed the celestial sphere’s shape to an ellipse. Its core features—namely, the Sun’s position above the Moon and the Sun being larger than the Moon—remained intact. This clearly suggests that the data underwent deliberate calculation and selective synthesis. According to his model, the celestial sphere has a minor diameter of 150,000 li (corresponding to its east–west width) and a major diameter of 180,000 li (corresponding to its vertical height). Its circumference, when calculated based on these two diameters, would be approximately 520,000 li13. This circumference figure is relatively close to several other relevant data points: namely, the 550,000 li circumference of the celestial sphere that he himself provided earlier; the value derived from his specification of “1390 li per degree” (1390 li × 365.25 degrees ≈ 508,000 li); and the 512,000 li calculated by earlier generations of professional astronomers14. Furthermore, in Chen Zhixu’s cosmic model, the Sun has a diameter of 835 li and the Moon has diameter of 670 li. These diameter values are not only largely consistent with the data showing that the Sun’s orbital length is 330,000 li (835 li × 365.25 celestial degrees ≈ 304,000 li) and the Moon’s orbital length is 240,000 li (670 li × 365.25 celestial degrees ≈ 244,000 li) that he himself provided; they were also inspired by Zhao Youqin’s view that (speaking of the Sun and the Moon) “their circumferences are in a 2:1 ratio 周徑相倍 (Gexiang Xinshu, p. 250)”—except that Chen Zhixu revised this ratio from a circumference ratio to a 2:1 ratio of their (the Sun and Moon’s) surface areas15. Thus, Chen Zhixu’s cosmic model appears to be the product of independent calculation and systematic synthesis, while remaining informed by the theoretical framework of Zhao Youqin.

This model serves as a crucial astronomical foundation for Chen Zhixu’s internal alchemy theory. Not only is the 90,000 li major diameter of its celestial sphere associated with “nine”—the “ultimate number of Heaven”; its 550,000 li circumference is also compatible with the concept of “the numbers of Heaven and Earth (天地之數 Tiandi zhi Shu)”. The concept of “the numbers of Heaven and Earth” originates from the tradition of the Hetu and Luoshu (河圖洛書 the River Map and Luo Chart, a study on numerical mysticism) in image-number Yijing studies. It is an important piece of symbolic and foundational knowledge in internal alchemy theory, linking the process of cosmic formation to the stages of internal alchemy cultivation. Among these numbers, one, two, three, four, and five are the generative numbers of the Five Elements 五行生數, representing the innate state (先天 the primordial state before the birth of the cosmos and all things) of humans and all things; while six, seven, eight, nine, and ten are the accomplishing numbers of the Five Elements 五行成數, representing their acquired state 后天 (the manifested state of humans and all things after their emergence). When the accomplishing numbers are added together with the generative numbers, their sum is fifty-five, which symbolizes the overall order of the universe (W. Zhang 2007, p. 36). As internal alchemy cultivation emphasizes the need for humans to return from the acquired state to the innate state, one plus four and two plus three both equal five; when combined with five itself, these—namely the two results (both equal to five) and the number five itself—form three sets of generative numbers of the Five Elements that represent the “innate state.”(see Figure 2) Through Chen Zhixu’s theoretical synthesis, this symbolic system was connected to the actual cosmic scale and supported by mathematical astronomy research. This not only reinforced the cosmological underpinnings of internal alchemy cultivation, but also verified the relationship of isomorphic structure between the Dao, Heaven, Earth, and the human body.

Based on this model, Chen Zhixu also rejected the Thirty-Six Heavens 三十六天 celestial realm theory from Lingbao Duren Jing. This theory is an important concept in Taoist cosmology16. It divides the heavens into thirty-six celestial layers, corresponding to the different orders of cosmic creation, the different grades of life forms across all things, and the different states attained by Taoist practitioners based on their cultivation achievements. The more complete a practitioner’s cultivation attainments are, the higher the celestial layer they can reach; furthermore, only the “Zhongmin” (Seed People 種民, devout believers in Daoism who can survive cosmic catastrophes) can attain the highest celestial layer, known as “Zhongmin Heaven 種民天”, thus avoiding the influence of the periodic destruction of the universe. This scripture also describes the separating distances between different celestial realms using exaggerated cosmic scales, aiming to inspire believers to become “Zhongmin”:

“One million three hundred and fifty-eight thousand li below Zhongmin Heaven lies the Formless Realm (無色界 Wusejie), which consists of four heavens. Thirty-six thousand li below the Formless Realm lies the Form Realm (色界 Sejie), which consists of eighteen heavens—within the Form Realm, there are six Subtle Dust Heavens (輕塵天 Qingcentian), six Fine Dust Heavens (細塵天 Xicentian), and six Coarse Dust Heavens (麤塵天 Cucentian). Thirty thousand li below the Form Realm lies the Desire Realm (欲界 Yujie), which consists of six heavens. Five hundred and twenty trillion li below the Desire Realm, there are 500 million celestial heavens (五億諸天 Wuyizhutian) and Eight Directional Circular Worlds (八圜世界 Bahuanshijie) formed through transformation and generation.”

種民天之下一百三十五萬八千里, 生無色界四天; 無色界之下三十六萬里, 生色界一十八天; 色界之內, 有輕塵六天, 細塵六天, 麤塵六天. 色界之下三十萬里, 生欲界六天, 欲界之下五百二十億萬里, 化生五億諸天, 八圜世界.

(Taishang Dongxuan Lingbao Wuliang Duren Shangpin Miaojing zhu, p. 410)

Chen Zhixu argued that the numerical values in the scripture were excessively exaggerated. In his annotations to the scripture, based on the aforementioned cosmic model, he pointed out that “The mentioned distances of several hundred thousand or tens of thousands of li regarding the celestial heavens formed through transformation (regarding the transformed celestial heavens) in this chapter are not actual numerical values 本章化生諸天所注幾百幾十萬里者, 非實有其數.” (Taishang Dongxuan Lingbao Wuliang Duren Shangpin Miaojing zhu, p. 426). Instead, these values are merely a figurative means that can be used to describe the ideal spiritual state of “those who attain the Dao and can abstain from sensual pleasures, thus being on par with sages and worthies 能絕欲樂, 即同聖賢.” He further emphasized that in reality, there is no actual “Zhongmin Heaven” that can shield one from calamities. Thus, Chen Zhixu not only rejected the cultivation practices advocated in Lingbao Duren Jing, such as disaster-warding prayers and rituals and scripture recitation, but also further deconstructed the cosmological foundation underlying this practice theory, replacing it with his own internal alchemy cosmic model.

3.4. The Adaptation and Integration of Astronomical Research in Chen Zhixu’s Internal Alchemy Theoretical System

Although Chen Zhixu provided an in-depth explanation of the importance of empirical astronomical research to internal alchemy cultivation at the theoretical level, it must be emphasized that Chen also contended that the astronomy’s ability to understand nature has its limitations—it cannot replace the teachings, practices, and methods of internal alchemy cultivation itself (they have undeniably higher authority), but rather serves as a supplementary tool that guides specific cultivation practices.

Chen Zhixu argued that sages (Shengren 聖人)17 are not only skilled at observing celestial phenomena, but also able to discern good and ill fortune by this means—and further seize and utilize the creative and transformative powers of the cosmos:

“The sage is one who is skilled at seizing and utilizing the creative and transformative powers of the cosmos… The cosmos lies within their grasp, and the transformation and generation of all things originate from their very being. The sage is one who is skilled at abiding in the Mean to regulate the external; they understand the pitch-pipes and the calendar and comprehend numerical principles.”

聖人者, 善奪造化也…宇宙在乎手, 萬化生乎身也. 聖人者, 善處中以制外也, 明律曆而知數也.

(Zhouyi Cantong qi Fenzhang zhu, p. 222)

“When a sage descends into the world, they observe the heavens above and examine the earth below, carefully discerns between Yin and Yang—taking Yin as the symbolic token and Yang as the vital essence… Heaven begets sages, who infer and examine the measures and calculations of the cosmos, taking actual effects as verification and symbolic signs as evidence. They observe the phenomena of the sun and moon, and imitate their forms and patterns… They set up a gnomon to measure shadows, taking this as a standard and model; they ascertain temporal rhythms (seasons and hours) through such observations, and discern good and ill fortune.”

聖人之降世也, 仰觀俯察, 精審陰陽, 以陰為符, 以陽為命…天生聖人, 推考度量, 以效為驗, 以符為證. 觀日月之象, 擬諸其形容… 立表測影, 以為格範, 占知時候, 察定吉凶.

(Zhouyi Cantong qi Fenzhang zhu, pp. 227, 228)

Thus, practical astronomical techniques constitute an important discipline that assists practitioners in attaining immortality and enlightenment. They elucidate the causal principles behind all things in the cosmos following the course of nature (including birth, aging, illness, and death) and the unlimited possibilities for cultivators to reverse the order of Yin and Yang and “become immortals or Buddhas 作仙作佛”: “The creative and transformative powers of the cosmos lie within my grasp; good and ill fortune are shaped by my cultivation. Following (the natural laws) leads to the generation of ordinary life, while reversing (them) leads to the formation of elixirs 造化在吾掌握, 禍福由我而修. 順則生人, 逆則生丹” (Wuzhenpian Sanzhu, p. 1009).

Chen Zhixu also modeled his more specific explanation of the relationship between the Dao, Heaven, Earth, and the human body after the “Four Greats in the Realm (域中四大 Yuzhong Sida)” cosmic structure from Tao Te Ching 道德經 (Daodejing Zhushi, p. 104). He maintained that the Dao is the Great Cosmos beyond the Heaven and Earth, while the human body is the Small Cosmos within Heaven and Earth—and there exists a manifestation of the Dao within the human body, thus forming a nested system of interlinked cosmic realms: Dao (Great Cosmos) → Heaven and Earth (Intermediate Cosmos) → Human Body (Small Cosmos) → Dao.

“Beyond Heaven and Earth (Intermediate Cosmos) lies the Great Cosmos… The present Heaven and Earth is but one entity within this Great Cosmos—just as humans are one entity within this present Heaven and Earth, and just as the Dao is one entity within the human body. Therefore, the human body is yet another Small Cosmos.”

天地之外有大天地焉… 今之天地, 屬大天地之中之一物耳, 即如人是今天地中之一物也, 即如道乃人身中之一物也. 是故人身又一小天地也.

(Taishang Dongxuan Lingbao Wuliang Duren Shangpin Miaojing zhu, pp. 50, 51)

Therefore, the exploration of the structure of Heaven and Earth constitutes an important pathway for cultivators to comprehend the Dao and themselves. One must “comprehend its transformations, thus grasping the patterns of Heaven and Earth; exhaust its numerical principles, thus defining the phenomena of all under Heaven 通其變, 遂成天地之文; 極其數, 遂定天下之象” (Zhouyi Cantong qi Fenzhang zhu, p. 268)—so as to attain, to the greatest extent possible, the ideal state of embodying and aligning with the Dao. This argument emphasizes the manifestation of the Dao through the structure of Heaven and Earth, and on a more fundamental level, elucidates the vital role of astronomical research in internal alchemy cultivation.

While traditional Chinese science reached its peak during the Song and Yuan Dynasties, Taoism yet entered a trajectory marked by a simultaneous decline in both its influence and participation in the field of science and technology, despite having a profound accumulation of research and once shining brilliantly in the studies of chemistry and mineralogy (Su 2016, p. 32). In the intellectual tradition of Taoism, the exogenous energy-acquiring factors (外向攫能性 Waixiang Jueneng Xing, a term describing the early Taoist practice of seeking energy and longevity through external substances like minerals and chemicals) (Jiang and Tang 2002, pp. 44, 48) conducive to the development of science gradually disappeared, and the theoretical system of external alchemy were incorporated into immaterial cultivation methods characterized by downplaying the exploration of nature and aimed at transcending mundane life (especially through the work of Zhang Boduan). Against this historical backdrop, Chen Zhixu’s work not only endowed his internal alchemy thought with robust theoretical dimensions and scientific elements, but also inherited and carried forward Taoism’s tradition of astronomical research.

Chen Zhixu also interpreted astronomical research and internal alchemy cultivation as a dialectical primary and secondary relationship, characterized by both opposition and mutual dependence. He pointed out that Heaven, the Earth, the Sun, and the Moon possess tangible form; that is, their movements and changes can be observed and calculated, and they will eventually perish. In contrast, the Golden Elixir is intangible: while it is the origin of the material world, it cannot be described within the conceptual frameworks of the material world, and is therefore without beginning or end:

“Those with fixed numerical determinism will inevitably face decline; those with fixed manifestations will inevitably perish… in contrast, only the Golden Elixir is the primordial pneuma: it transforms without form or appearance, transcending the realm of the Five Elements, exceeding the limits of image-number, and abides in the realm of cosmic creation and transformation.”

有成數者必有否, 有定象者必有終…唯金丹乃元始一炁, 變化無形無象, 超五行之外, 出象數之限, 立乎造化之象也.

(Taishang Dongxuan Lingbao Wuliang Duren Shangpin Miaojing zhu, p. 427)

While cultivators need to “realize the Dao through Shu (術 cultivation techniques) 以術證道”, it is nonetheless necessary to adhere to the principle that “Cultivation techniques take the Dao as their substance (Zhu), while the Dao takes cultivation techniques as its function (Yong) 術以道為主, 道以術為用.” (Jindao Dayao, p. 46).

Although the “Shu” here refers to the “cultivation technique of inverting Yin and Yang 顛倒陰陽之術”, Chen Zhixu further noted that the crux of this technique lies in mastering the “subtle mechanism of the unpredictable nature of Yin and Yang 陰陽不測之機” to achieve the transcendent goal of “uniting with the Dao in accordance with the sun and moon 以道而合於日月”. And “uniting with the sun and moon” means one should choose the timing of cultivation based on changes in celestial phenomena:

“To unite with them, when the moon is born in Geng, metal is at its peak and water is clear, signifying the gathering of metal on the third day (in a lunar month). Hence, it is said to unite with the brilliance of the sun and moon.”

合之者, 月生於庚, 則金旺水清, 乃採金於三日, 故云與日月合其明.

(Jindao Dayao, p. 46)

Therefore, from Chen Zhixu’s perspective, the mastery and understanding of astronomical phenomena are undoubtedly crucial components of the “techniques” and “functions” that serve as auxiliary tools. However, his ultimate goal remained the realization of unity with the Dao, which is the “master.” This Dao is precisely “the Dao of the Golden Elixir”.

In conclusion, Chen Zhixu’s adoption of secular astronomical knowledge was selective. The principle of internal alchemy has higher authority, and astronomical concepts are only used to provide support for it, rather than surpassing the teachings of internal alchemy. For instance, Zhao Youqin rejected the notion that lunar and solar eclipses were portentous celestial events that affect human affairs. Instead, he viewed them as mundane astronomical phenomena governed by objective astronomical principles and unrelated to human activities, which could be computed and predicted—and thus required no rituals for disaster prevention: “Lunar and solar eclipses are merely an inherent regularity of the sun–moon orbital crossings. Even in times of great peace and prosperity, they cannot be avoided—thus can be predicted through calculations. 日月之食, 乃所行交道常數, 雖太平盛世, 有所不免, 故可以籌策先推” (Gexiang Xinshu, p. 250). However, given the importance of lunar and solar eclipses’ temporal windows in internal alchemy cultivation—with solar eclipses occurring on the Hui and lunar eclipses on the Shuo, both being crucial periods for internal alchemy cultivation—Chen Zhixu maintained that eclipses would exert special influences on practitioners’ physical and spiritual states and thus required responsive adjustments: “The so-called ‘rescue’ consists of observing astronomical phenomena to perceive changes in fire times, and providing advance warning and vigilance所謂救者, 觀乎天文以察時變, 預為之儆戒耳” (Taishang Dongxuan Lingbao Wuliang Duren Shangpin Miaojing zhu, p. 431). Chen Zhixu’s practice of defining the size of the celestial sphere as 550,000 li and calculating the diameters of the sun and moon also contradicted the theoretical propositions of Zhao Youqin.

Furthermore, given his empirically grounded intellectual stance and the absence of evidence, Zhao Youqin did not provide numerical values describing the apparent shapes of the Sun and Moon. He also argued that there was no physical celestial sphere with clear boundaries: “The Heaven cannot be perceived in its true form… The true form of Heaven can never be known 天非可見其體…天不可知其體”. The claim that “Heaven is like a chicken egg” in the Hun Tian theory is merely a metaphor, intended to facilitate scholars’ visualization and description of the structure of Heaven and Earth: “The so-called ‘Heaven is like a chicken egg’ refers to nothing more than a metaphor for the Heaven enclosing the Earth 所謂天如雞子者, 喻其天包地外而已” (Gexiang Xinshu, p. 229). In addition, the celestial measurement values derived from the Gougu method to which the figure of 550,000 li was analogized had already been discarded in calendar calculation during the Yuan Dynasty—making them an outdated intellectual tradition in astronomical measurement and calendar calculation (Fu 1988).

To sum up, Chen Zhixu’s theoretical propositions demonstrate that internal alchemy cultivation, as a religious practice, is fundamentally different from empirical astronomical research in their respective intrinsic nature. While Chen Zhixu incorporated a wealth of astronomical knowledge when constructing his internal alchemy theoretical system, he also adopted and interpreted such knowledge selectively, guided by the needs of internal alchemy cultivation. This reflects the distinct divergence in research stances between his and that of Zhao Youqin.

4. Conclusions

As an influential Taoist scholar of the Yuan Dynasty, Chen Zhixu developed his internal alchemy theory by combining traditional and innovative elements. This is clearly demonstrated through the three distinct levels of his application of astronomical knowledge. At the level of its basic theoretical framework, Chen inherited and developed the cosmological symbolism model of traditional internal alchemy theory. At the same time, he provided specific and detailed practice steps and precautions, and refined the correspondence between the alchemical fire times and astronomical phenomena in internal alchemy theory practice, thus representing a break from the obscurity and abstruseness of previous internal alchemy theory works.

Furthermore, within the framework of traditional correlative cosmology, Chen Zhixu incorporated systematically empirical astronomical knowledge (including observational data and calendar calculation values) to enrich the details of his arguments. By doing so, he not only expanded the astronomical dimension and cosmological foundation of traditional internal alchemy theory, but also strengthened the inherent correspondence between internal alchemy cultivation and astronomical research. Additionally, he critiqued the other-power-dependent religious approach advocated in the Lingbao Duren Jing from an experiential and astronomy-based perspective, thereby providing a rational justification for internal alchemy cultivation to become the mainstream practice of Taoism in his era. The metaphysical structure of the universe based on Hun Tian theory that he proposed also connects the “Heaven–Earth numbers” in the image-number Yijing tradition to the calculations of mathematical astronomy. In doing so, he critiqued the mainstream Taoist celestial realm theories with exaggerated cosmic scales and established a relatively rational astronomical model for his internal alchemy theory. This work is also one of the boldest and most innovative parts of his theoretical work. Against the backdrop of the decline of the Taoist scientific tradition during the Song and Yuan Dynasties, Chen Zhixu’s efforts adopted the Taoist astronomical research tradition and consolidated the epistemic foundation of internal alchemy.

However, as an internal alchemy theorist, Chen Zhixu’s religious beliefs imposed clear boundaries to his acceptance and integration of astronomical knowledge. For him, astronomical research could only serve as an auxiliary means—that is, it could never replace the goals, models, methods, and practices of internal alchemy cultivation, nor could their “substance–function” relationship be inverted. This marked a notable divergence in research stances between Chen Zhixu and his master, Zhao Youqin. Therefore, Chen’s case demonstrates the structural subordination of natural research to religious practice within the Taoist intellectual tradition. This situation differs both from Joseph Needham’s positive assessment of the relationship between Taoism and science, and from Nathan Sivin’s fundamental skepticism (Sivin 1978).