It is a common misconception that AD years were set so that Jesus was born in 1 AD. 1 AD was set to meet two criteria: With recorded history at the time (in 532 AD), it was known that Jesus was alive on January 1st, 3BC.
So 1 AD was set to the next year that allowed 366-day years to occur in AD years exactly divisible by 4.
The Equinox is the point where the Sun crosses the Equator making day and night equal.
The Calendar Year is 365 days except if the year number is divisible by four evenly, this being a Leap year of 366 days.
In the Old Style this was March 25th and was changed to January 1st (New Style) in England in 1752 when changing from the Julian to Gregorian calendar.
New Years Day was changed to January 1st in Scotland in 1600.
1 AUC is the same as 753 BC in the Julian calendar.
It was not until 532 AD that the Pope, with significant influence, replaced Julian AUC years with Julian AD years.This calendar is so accurate that a further adjustment will not be required until 4100 or soon after. This system is said to have been introduced into England by St. This was corrected in 1582 when Pope Gregory ordained that October 4th would be followed by October 15th, making the 10 day correction, and that only every fourth centennial year should be a Leap Year.The following excellent and accurate article is reprinted from the Australian Es E-2c (Easy To See) Calendar 1998. The calendar as we know it has evolved from a Roman calendar established by Romulus, consisting of a year of 304 days divided into 10 months, commencing with March. was made to consist of 445 days to adjust for earlier faults and is known as the "Year of Confusion". This is known as the Gregorian calendar and is the one we now use.The method for calculating Easter date also mirrors calendar changes, so I have included that also.Many thanks must go to Ron Mallen for his tireless, meticulous and scientific process in researching this history.It started as a year of 10 lunar months, and soon changed to a lunar year of 12 months.