From the Julian Calendar to the Gregorian Calendar
Before Christ Jesus was born, something must be well prepared, the calendar.
So, Gaius Julius Caesar tried to review the calender Romans had bee using till his leadership in the Roman Republic.
The Julian calendar, introduced by Julius Caesar in 46 BC (708 AUC), was a reform of the Roman calendar. It took effect in 45 BC (709 AUC). It was the predominant calendar in most of Europe, and in European settlements in the Americas and elsewhere, until it was refined and superseded by the Gregorian calendar. The difference in the average length of the year between Julian (365.25 days) and Gregorian (365.2425 days) is 0.002%.Then when the new era for Christians and mankind began around 1500, some people started to modify the calender, resulting in creation of the Gregorian calendar.
The ordinary year in the previous Roman calendar consisted of 12 months, for a total of 355 days. In addition, a 27-day intercalary month, the Mensis Intercalaris, was sometimes inserted between February and March. This intercalary month was formed by inserting 22 days after the first 23 or 24 days of February; the last five days of February, which counted down toward the start of March, became the last five days of Intercalaris. The net effect was to add 22 or 23 days to the year, forming an intercalary year of 377 or 378 days.[4]
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If too many intercalations were omitted, as happened after the Second Punic War and during the Civil Wars, the calendar would drift out of alignment with the tropical year. Moreover, because intercalations were often determined quite late, the average Roman citizen often did not know the date, particularly if he were some distance from the city. For these reasons, the last years of the pre-Julian calendar were later known as "years of confusion". The problems became particularly acute during the years of Julius Caesar's pontificate before the reform, 63–46 BC, when there were only five intercalary months (instead of eight), none of which were during the five Roman years before 46 BC.
Caesar's reform was intended to solve this problem permanently, by creating a calendar that remained aligned to the sun without any human intervention. This proved useful very soon after the new calendar came into effect. Varro used it in 37 BC to fix calendar dates for the start of the four seasons, which would have been impossible only 8 years earlier.[6] A century later, when Pliny dated the winter solstice to 25 December because the sun entered the 8th degree of Capricorn on that date,[7] this stability had become an ordinary fact of life.
http://en.wikipedia.org/wiki/Julian_calendar#Motivation
The Gregorian reform modified the Julian calendar's scheme of leap years as follows:
Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100, but these centurial years are leap years if they are exactly divisible by 400. For example, the years 1700, 1800, and 1900 are not leap years, but the year 2000 is.[6]
In addition to the change in the mean length of the calendar year from 365.25 days (365 days 6 hours) to 365.2425 days (365 days 5 hours 49 minutes 12 seconds), a reduction of 10 minutes 48 seconds per year, the Gregorian calendar reform also dealt with the accumulated difference between these lengths. Between AD 325 (when the First Council of Nicaea was held, and the vernal equinox occurred approximately 21 March), and the time of Pope Gregory's bull in 1582, the vernal equinox had moved backward in the calendar, so that in 1582 it occurred about 11 March, 10 days earlier than 21 March. The Gregorian calendar therefore began by skipping 10 calendar days, to restore 21 March as the date of the vernal equinox.
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The calendar was a reform in 1582 to the Julian calendar. It was introduced by Pope Gregory XIII, after whom the calendar was named, by papal bull Inter gravissimas dated 24 February 1582.[4] The motivation for the adjustment was to bring the date for the celebration of Easter to the time of the year in which the First Council of Nicaea had agreed upon in 325.
http://en.wikipedia.org/wiki/Gregorian_calendar#Gregorian_reform
However, without an influence of Copernicus, the Gregory calendar might not be successful
Nicolaus Copernicus (1473 – 1543) was a Renaissance mathematician and astronomer who formulated a model of the universe that placed the Sun rather than the Earth at its center.[a] The publication of this model in his book De revolutionibus orbium coelestium (On the Revolutions of the Celestial Spheres) just before his death in 1543 is considered a major event in the history of science, triggering the Copernican Revolution and making an important contribution to the Scientific Revolution.So, about 50 years before the birth of Christ Jesus, Julius Caesar had actually prepared a better calendar system for the glorious coming of the Son of God.
http://en.wikipedia.org/wiki/Nicolaus_Copernicus#Heliocentrism
And about 50 years after Columbus discovered the New World and open the new era for Christians and Judaists as well as mankind, Copernicus' work was published, leading to formulation of the better calender, the Gregorian calendar.
It looks like having matched a certain divine plan.
Conversely, we had better admit that the Christian/Judaist history had two great epochs: one from AD 1 to around 1500 and another from around 1500 to around 2000 or today.
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Mat 8:18 Now when Jesus saw great multitudes about him, he gave commandment to depart unto the other side.