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.
Using the Celestial Sphere as the reference is called Sidereal Time. A Sidereal Year would be the time it takes for the same reference star to be in the same position overhead at the Vernal Equinox A Sideral Year is slightly longer than a normal year (a Solar Year) it takes approximately 365.2465 days.