Lunar mansion
Xū
Emptiness
An almanac describes traditional day-types. It cannot decide health, money, law, marriage or children. Burial, marriage and medical items on these pages are what a book states, never advice.
In the classical sources
一元甲子日起虚以子象鼠而虚為日鼠也
The first 元 starts its 甲子 day at 虛, because 子 figures the rat and 虛 is the sun rat.
協紀辨方書 卷一
About this entry
虛 is the starting point of the 420-day round, as far as the books can say. 協紀辨方書 卷一 and 星厯考原 卷五 open the first 元 with 甲子 on 虛, on the reasoning that 子 is the rat. Both admit that the first year, month and day cannot be traced.
The calculator needs a start, so it follows modern almanac convention and places 虛 on a 甲子 day, with the sun group on Sunday. 虛 belongs to that group alongside 昴, 星 and 房 and was therefore one of the 密 days that 卷三十六 treats with skepticism. Its neighbors are 女 and 危.
Where this text comes from
The Chinese follows the Wikisource typed text of the Siku copy, under its CC BY-SA terms. Statements about the calculator describe its own rules, and modern practice is labeled as modern.
- 協紀辨方書 卷一
Retrieved 2026-11-09
- 協紀辨方書 卷三十六
Retrieved 2026-11-09
- 星厯考原 卷五
Retrieved 2026-11-09
The English here is our own plain wording. Lists keep the items of the source.