Why did the priests observe the movement of heavenly bodies?

The priests of ancient countries were considered the founders of astronomy. They daily observed the movements of celestial bodies, as a result of which they predicted the onset of floods and eclipses. Such predictions were necessary in the conduct of cattle breeding and agriculture. This knowledge is especially important for residents of countries with huge rivers, in order to know the moment of flooding and to hide from the waves of a raging river.
The astronomer priests had tremendous power over the people, even the kings listened to them.