Book of Astronomy

Section Four: On the Yin and Yang Affiliations of the Seven Luminaries

The Sun, Saturn, Jupiter, and Mars belong to Yang Yang original: 陽 (yáng); representing the active, masculine, or solar principle.. The Moon and Venus belong to Yin Yin original: 陰 (yīn); representing the passive, feminine, or lunar principle.. These two luminaries the Moon and Venus possess an abundance of moistening energy moistening energy original: 潤氣 (rùn qì); a quality associated with the Yin principle, implying coolness and fluid growth.; therefore, they are classified as Yin.

Mercury original: 水星 (shuǐ xīng); literally "Water Star" becomes Yang when it encounters a Yang planet. It becomes Yin when it encounters a Yin planet.

According to another theory, if Mercury rises before the Sun, it is considered Yang. If it sets after the Sun, it is considered Yin.

Yet another theory states: if Mercury is positioned between a person’s Ascendant Ascendant original: 安命宮 (ān mìng gōng); literally the "Palace where Life is Settled," the starting point of the astrological chart. and the tenth house, it is Yang. If it is located between the descendant descendant original: 對宮 (duì gōng); literally the "Opposite Palace," the house directly across from the Ascendant. and the fourth house, it is also Yang. In the remaining six houses, it belongs to Yin. This division refers to the quadrants of an astrological chart; the areas between the Ascendant/Midheaven and Descendant/IC were often assigned specific gendered or functional qualities in medieval astrology.