Rivers were used to turn watermills and the Romans even used geothermal water for heating. Until the middle of the 18th century renewable sources of energy were the only forms of energy available, but then, with the advent of the Industrial Revolution, fossil fuels began to be exploited.
The Sidereal Zodiac is the position of the sun referenced against the star background, as a measure of the flow of time. The framework for the star background is the constellations the sun passes in front of. This is the one astronomers use.
The sidereal month is the actual time it takes the Moon to orbit the Earth, but the lunar month is how long it takes for us to notice the completion of the orbit (to return to a moon phase) due to the Earth also orbiting around the Sun.