Tai Yin, the great yin, is the Moon given a place among the fourteen major stars, the direct counterpart to Tai Yang the Sun and, with it, one of only two stars in the whole system that name an actual celestial body rather than an abstracted office or quality, a distinction that gives both stars a waxing and waning intensity across the birth chart's twelve houses tied to the timing of birth rather than to palace company alone. Where Tai Yang is read outward, for visibility and public standing, Tai Yin is read inward, for introspection, quiet accumulation and a wealth built gradually and privately rather than displayed, a genuinely complementary rather than opposed pairing in the tradition's own framing.
Tai Yin also carries, by the reading practice's established convention, an association with the native's female relatives, most commonly the mother, mirroring Tai Yang's own association with the father, a symmetry that follows the wider yin and yang polarity organising a great deal of traditional Chinese cosmological thought well beyond astrology alone. The star's brightness in a given chart is read as strongest for a birth around the night's own midpoint and weaker for a birth nearer midday, the same kind of hour dependent variation in strength that governs Tai Yang's own solar reading, only inverted to the opposite half of the day.