The mare and the Heavenly Coach-And-Four

Here in the West we are not familiar with the work of 烏恩溥 Wu En-pu, but in China's world of Yixue he is a well known name. His speciality is the discovery of astronomical phenomena in the Yijing, like for instance hexagram 22, which Wu sees as a comet. In the only book I have of him, 周易 - 古代中國的世界圖式 ('Zhouyi - Ancient China's design of the world'), he gives a lot of his findings. I find much of his arguments far-fetched. With Wu it looks like 'I want to find it, therefore I shall find it'. But it is good to be acquainted with his ideas, even though you do not agree with them. 

Let us take the mare from hexagram 2 as an example of Wu's way of thinking. Because the word for mare, pinma 牝馬 is made up of two characters, 'female' and 'horse', and this is important for what will follow, I will speak of it as 'the female horse', however odd this may sound. Wu says about pinma 牝馬 (p. 52 of the forementioned book):

牝馬當指天駟，即房星.
'Female horse' is a reference to Tianma, 'The Heavenly Coach-And-Four'; Tianma is the constellation Fang 房.

This sentence already needs some clarification, otherwise it is hard to understand what comes next. Fang is a Chinese constellation, it is situated in our Western constellation Scorpio, and it is the name giver of the fourth xiu 宿, the fourth lunar mansion. It is part of the constellation qinglong 青龍 or canglong 蒼龍, the Azure Dragon.

《爾雅》:"天駟，房也", 郭璞 (276-324) 注: "龍為天馬，故房四星，謂之天駟."
The Erya says: "Tianma 天駟 is Fang 房"; Guo Pu (276-324) adds: "The dragon is the Heavenly horse; because the constellation Fang has four stars it is called 'the Heavenly Coach-And-Four'."

房星共四星，屬東方蒼龍七宿的第四宿，為龍腹。
The constellation Fang consist of four stars and is the fourth lunar mansion in the Eastern constellation Azure Dragon, which covers seven lunar mansions; Fang represents the stomach of the dragon.

天駟或房星何以稱為 "牝馬" ? 《石氏星經》: "房南二星間為陽環，其南曰太陽道;北二星間為陰環，其北為太陰道." 原來房四星是太陽道和太陰道的分界線，天駟而稱 "牝馬", 正是分陰、分陽的標記。
Why is the Heavenly Coach-And-Four, the constellation Fang, 'the female horse'? The Shi Shi Xing Jing ('The Book of Stars from Mr. Shi', written by Shi Shen 石申, around 300 B.C. HM) says: "The space which is formed by the two Southern stars of Fang is the yang circle, this South is called 'the Way of Great Yang'; the space which is formed by the two Northern stars of Fang is the yin circle, this North is called 'the Way of Great Yin' ". Originally the stars of the constellation Fang are considered as the boundary between the Way of Great Yang and the Way of Great Yin; the  'Heavenly Coach-And-Four' is therefore called 'the female horse', because it is the demarcation between the yin and yang sides.

Wu means this: the word for mare is pinma 牝馬. Pin 牝 is 'female', that is what it means. But ma 馬 is 'horse', and a horse is yang 陽, male. In the Shuogua 說卦 we read, "乾為馬": "Qian (yang) represents 'horse' ". With pinma 牝馬 we have female and male, and because of that it can serve as another name for the Heavenly Coach-and-Four, a constellation which in the old days was seen as the division between yin and yang.

By the way, taiyangdao 太陽道, 'the Way of Great Yang', and taiyindao 太陰道, 'The Way of Great Yin' can also be translated as 'the sun's course' and 'the moon's course'. But I am not sure if that is meant here, therefore I chose to translate it literally.

Far-fetched? You decide. In any way this text tought me quite a lot about Chinese astronomy and astrology. If it really has something to do with the Yijing is not always important. Inessentials can contribute a lot to the understanding of what is essential.