However, there are still small changes accumulating, and one day we shall have to By 1582 the vernal equinox had moved another ten days and Pope Gregory established a new calendar, and this change is the reason for having an extra day in every leap year. The Emperor Constantine established dates for theĬhristian holidays, but Easter is based on the date of the vernal equinox which varies every year because the equinox is an astronomical event. In 325 CE the spring (vernal) equinox had moved to March 21.

Calendars have had to be altered regularly.

The problem was taken up by astronomers in the Middle East and India who recognized that precession gradually altered the length of the year. In the Mediterranean, Hipparchus made the earliest calculations of precession in about 160 BCE. The Earth's axis completes a circuit about once every 26,000 years This movement produces a slow 'wobble' which means that the positions of the stars complete a cycle of about 26,000 years. Precession is due to the gradual movement of the Earth's rotational axis in a circle with respect to the fixed stars. Most comprehensive calendar was the Dayan Calendar compiled in the Tang Dynasty (616-907 CE) well ahead of any such development in Europe. In the fifth century CE the scholar Zu Chongzi created the first calendar which took precession into account, and the This problem is called Precession and was recorded by Chinese historians in the fourth and fifth centuries CE. Over such a long period of observation, Chinese astronomers became aware that theirĬalendar was not accurate, and by the second century CE it was recognised that the calendar became unreliable every 300 years. However, traditional Chinese records suggest the origin of a calendar of 366 days depending on the movements of the Sun and the Moon as early as 3,000 BCE. They show a 12 month year with the occasional occurrence of a 13th month. The earliest archaeological evidence of Chinese calendars appears about 2,000 BCE. Their base 60 fraction system which we still use today (degrees / hours, minutes and seconds) was much easier to calculate with than the fractions used in Egypt or Greece,Īnd remained the main calculation tool for astronomers until after the 16th century, when decimal notation began to take over. The Assyrian winged man-headed bull had the strength of a bull, the swiftness of a bird and human intelligence.įrom about 700 BCE the Babylonians began to develop a mathematical theory of astronomy, but the equally divided 12-constellation zodiac appears later about 500 BCE to correspond to their year of 12 months of 30 days each. The constellation Taurus, the bull, a symbol of strength and fertility, figures prominently in the mythology of nearly all early civilizations, from Babylon and India to northern Europe.

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