What did Pope Innocent III mean by comparing papal authority to the Sun?

Pope Innocent III used the metaphor of the Sun and the Moon to illustrate the hierarchical relationship between the papacy and secular rulers. In this analogy, he represented papal authority as the Sun and the power of lay princes as the Moon.1

While Innocent acknowledged that both powers were established by God, he argued that the Moon derives its light from the Sun. By extension, he asserted that royal power acquires its greatness, dignity, and legitimacy from the authority of the pope. This striking image served to emphasize his vision of papal supremacy, reinforcing his claim that the pope held authority not merely as a representative of man, but as the representative of the true God on Earth.1