four-part

The four parts in singing are soprano,alto,tenor and bass.

唱个声部是女高音、女低音、男高音和男低音。

In fact, they divided Heaven into four parts and each part is composed by septuple Primary Stars.

西方七星奎、娄、胃、昂、毕、角、参形状如虎，称西宫为白虎。南方井、鬼、柳、星、张、翼、轸为鸟形，称朱雀。