The referred "four gods" are those who guard east, west, south and north,the four corners of the earth Seiryuu, Byakko, Suzaku and Genbu. Each god divided up the sky into four equal quadrants and the twenty eight Seishuku withim them were separated into seven.
According to ancient Chinese astronomy, the sky was divided into four quadrants, each quadrant representing a season of the year. These quadrants are then each divided into 28 different segments, called "sheishuku". The quadrants themselves are associated with colored animals deities that serve as guardians. These are Suzaku The Red Bird, Seiryuu The Blue Dragon,Genbu The Black Tortoise or Warrior and Byakko The White Tiger. The unique circular formation of the quadrants and constellations has many different explanations.