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.
A mean sidereal day is 23 hours, 56 minutes, 4.0916 seconds (7001239344699000000â 23.9344699 hours or 6999997269580000000â 0.99726958 mean solar days), the time it takes Earth to make one rotation relative to the vernal equinox.