4 Symbols & the 28 Mansions
The four symbols, which could be translated 'signs', are the traditional way of dividing the night sky. Each quadrant then gets subdivided further into seven 'mansions' (宿), which is something like a resting place or a temporary lodging, making a total of 28. They are linked to the movement of the moon, so that each mansion is crossed in turn as the moon orbits the earth.
4 Books of Zhu Xi
Zhu Xi (1130-1200) was a Confucian scholar of the Southern Song (1127-1276). Incredibly learned and prolific, he ushered in a Neo-Confucian revival. His commentaries on the Four Books, which he singled out as the core classics of the Confucian canon, became prescribed reading for government officials.
