Abstract :
Ancient time determining the unit of time we call the day is pretty simple. It´s the interval between two successive sunrises. Several Mediterranean civilisations divided the day into 12 daylight hours and 12 night time hours. The year was also an important span; agriculture and many other social customs depend on knowing the recurrence of the equinoxes, when the period of daylight equals that of night, and the solstices, when the sun is highest or lowest in the sky at noon. Several ancient cultures, especially the Babylonian and Chinese, showed great sophistication in measuring longer intervals, such as those marking off lunar and solar eclipses. Even the advance of the equinoxes the slow, steady shift of the coming of the equinoxes caused by the slewing of Earth´s rotational axis, amounting to about one-twelfth of the sky every 2,000 years was known in antiquity.
