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

唱歌的四是女高音、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.

西七星奎、娄、胃、昂、毕、角、参形状如虎，称西虎。南的井、鬼、柳、星、张、翼、轸联鸟形，称朱雀。