What does an auspicious day mean in the old calendar?

Building, full, flat and black; In addition, danger, determination and yellow; Can be used, opened and used; Sealing is not the same as breaking.

There are twelve stars in this formula, which are called ecliptic day and underworld day. It is called "building divided by twelve straight lines" and "building divided by twelve passengers". Most of the proprieties and taboos in the yellow calendar are based on it in turn.