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.
Sidereal Time. Sidereal time is equal to the hour angle of the catalog equinox and is a direct measure of the diurnal rotation of the Earth. Apparent sidereal time is defined by the intersection of the true equator of date with the ecliptic of date and is affected by the precession and nutation of the axis of the Earth. Mean sidereal time is measured against the mean equinox of date and is only affected by precession. The tabulated sidereal times are given in hours, minutes and seconds, rounded to the nearest 10 -4 second.