The reason behind this is that the seasonal and the astronomical actions do not repeat at a precise number of full days, a calendar in a year if had the exact number of days would over time shift according to the event it was supposed to follow. Only by adding an additional month or day in a year, overtime flow can be solved. A year which does not have an extra month or days or simply we can say that if it is not a leap year it is called as leap year.

February 29 is usually called a leap day as it happens after every four year. As the Earth Revolve around the sun in exactly 365 days so that’s why a day is added in a month or year as a corrective measure. The Julian calendar had too many leap days thus raising the number of days among the vernal equinox of March 21, during the council of Nicaea in AD 325 its scheduled date was noted. But when Gregorian calendar was introduced it allowed for relocation with the equinox, however, when the change was made many days were dropped.

Even today no calendar is perfect every year they are influenced by the seconds, minutes, hour, days and month. To make it more perfect or correct, new rules have to be followed in Gregorian calendar complicating the number of days in the calendar even much more.

However it will need some good modifications in thousands years or even more than that. But for the tropical year it is around 365.242199 days, because of the power of the other planets it differs every year.

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1. Chinese Calendar

Moreover Chinese calendar is also used for the purpose of astrology like determining the auspicious date for a wedding and any other good work to be done in near future. The phases of the moon can also be determined as it follows the cycle of the moon once in a month. This year in Chinese calendar is considered to be the year of Earth Rat starting from 7 February, 2008 to 25 January, 2009.

The earliest facts of the Chinese calendar is originated on the oracle bones in late second millennium BC of the Shang dynasty which give the impression that the lunisolar year consists of 12 months, with likely intercalary of thirteen, or at times even fourteen, added empirically to avoid the calendar flow.

For recording the day, Sexagenary cycle was already in use. In that period the year starts on the first new moon. The spring and the autumn chronicles provide the better way to understand the type of calendar used in the Zhou dynasty.

In a year there were usually 12 months which consists of 29 and 30 days alternatively but from time to time an additional was also added to come up to the flow between the calendar and the actual moon cycle and also at the end of the year intercalary months were also added randomly. Later on Gregorian calendar was adopted as an official on January 1912 but the general public was still using the traditional calendar.

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1. Leap Year