The current calendar recognized worldwide as the Gregorian calendar most likely had its origins in the lunar calendar of the Greeks and possibly even the Greeks had identified with earlier sources.
The lunar year is a poor reflection of the solar year however. The Romans however are responsible for the basic form and names of the months which have come down to us today and the calendar adopted by Julius Caesar survived as a standard for centuries before the adoption of the Gregorian calendar.
The Calendar of Romulus
Romans attributed the first calendar to Romulus, the legendary founder of the city of Rome. This calendar consisted of ten months with irregular number of days in each month and was not lunar. The months for Romulus's calendar were named for gods and goddesses, the order in which the month appeared in the calendar, and in the case of Aprilis (April) , meaning “opening”, the flowering of springtime. Martius (March) was associated with the vernal equinox.
These ten months constituted 304 days of the year. There were 61 days of winter between December, the last month of the year, and March, the first month of the year unassigned to any month.
The Calendar Becomes One Having Twelve Months
Numa Pompilius, one of the legendary kings of Rome, who followed Romulus added the months of Ianuarius (January) named after the god Janus, the god of the doorway, and February, named after the Latin term februum, which means purification, the purification ritual Februa held during this previously unnamed winter period.
With the addition of January and February and the reassignment of the number of days in the months the calendar became more representative of a lunar calendar encompassing 355 days. The oddity being that the months called September, October, November, and December no longer represented the seventh (Sept-), eighth (Oct-), ninth (Nov-) and tenth (Dece-) months of the year.
Reforms of Julius Caesar
The lunar year of 355 days would cause a significant “drift” between calendar dates and season. Thus, it became a custom to insert a intercalary month periodically to realign date to season. To the Romans this became a political issue. Officials were elected to terms of office based on calendar dates. Thus, the officials responsible for authorizing the intercalary month could either shorten or lengthen terms of office of officials based on their political leanings.
The reforms were designed to prevent such abuses. The number of days in the months were adjusted to reflect a 365 day year with the provision for an additional day to be added to unfortunate, as Romans considered even number unlucky, twenty-eight day February.
The Introduction of the Gregorian Calendar
The assumption made with the establishment of the Julian calendar was that the time between Vernal Equinoxes is 365.25 days. Whereas in fact the time differs by about 11 minutes less. The importance to the leaders of the Roman Catholic Church had to do with how the feast of Easter was computed. Easter is computed as the first Sunday following the first full moon after the vernal equinox. In 325 A.D. at the time of the First Council of Nicaea, the vernal equinox occurred on March 21st. At the time when Pope Gregory promulgated the bull establishing the new calendar in 1582, the vernal equinox was on March 11th .The situation would persist so that theoretically Easter would fall close to or on Christmas.
The Gregorian calendar made this ten day adjustment to the date of the year and incorporated a new way of determining leap years. Every four years was a leap year except for the century years where the century years were divisible by 400. Thus, 1600, 2000, and 2400 would be leap years but 1700, 1800, 1900, 2100 would not be.
Their was a great resistance to the adoption of the system due to the perception of the “loss of days”. The day following March 11th for example became March 21st. Yet over the next 150 years or so the Gregorian calendar became not only a religious standard but also an international civil standard. Amazingly this simple formula resulted in only an 11 second difference in computing the year 2000 and will not require a "readjustment" for thousands of years.
Reference:
- Duncan, D.E. (1999). Calendar Year. Humanity's Epic Struggle to Determine a True and Accurate Year. New York: Harper Perennial ISBN 0-380-79324-5.
Tony De Vita - My basic background was in mathematics. Having received a B.S. summa cum laude, from Wilkes College, Wilkes-Barre, Pa. My first job was ...
