For stars sake just check out the calandrical history!! No A.D. isn't After Death!! The actual calander went through a evolution of its own.
In the year 46 BC, the Greek Sosigenes convinced Julius Caesar to reform the Roman calendar to a more manageable form. At this time, Julius also changed the number of days in the months to achieve a 365 day year. In order to "catch up" with the seasons, Julius Caesar also added 90 days to the year 46 BC between November and February (Vardi 1991, p. 238).
The Julian calendar consisted of cycles of three 365-day years followed by a 366-day leap year. Around 9 BC, it was found that the priests in charge of computing the calendar had been adding leap years every three years instead of the four decreed by Caesar (Vardi 1991, p. 239). As a result of this error, no more leap years were added until 8 AD. Leap years were therefore 45 BC, 42 BC, 39 BC, 36 BC, 33 BC, 30 BC, 27 BC, 24 BC, 21 BC, 18 BC, 15 BC, 12 BC, 9 BC, 8 AD, 12 AD, and every fourth year thereafter (Tøndering). The UNIX command cal incorrectly lists 4 AD as a leap year (Vardi 1991).
The Julian calendar was switched over to the Gregorian starting in 1582, at which point the 10 day difference between the actual time of year and traditional time of year on which calendrical events occurred became intolerable. The switchover was bitterly opposed by much of the populace, who feared it was attempt by landlords to cheat then out of a week and a half's rent. However, when Pope Gregory XIII decreed that the day after October 4, 1582 would be October 15, 1582, the Catholic countries of France, Spain, Portugal, and Italy complied. Various Catholic German countries (Germany was not yet unified), Belgium, the Netherlands, and Switzerland followed suit within a year or two, and Hungary followed in 1587.
Because of the Pope's decree, the reform of the Julian calendar came to be known as the Gregorian calendar. However, the rest of Europe did not follow suit for more than a century.
The Protestant German countries adopted the Gregorian reform in 1700. By this time, the calendar trailed the seasons by 11 days. England (and the American colonies) finally followed suit in 1752, and Wednesday, September 2, 1752 was immediately followed by Thursday, September 14, 1752. This traumatic change resulted in widespread riots and the populace demanding "Give us the eleven days back!"
Sweden followed England's lead in 1753. Russia, however, did not follow suit until 1918, when January 31, 1918 was immediately followed by February 14th. In fact, however, the USSR is not on the Gregorian calendar, but on a more accurate one of their own devising. The USSR calendar is designed to more closely approximate the true length of the tropical year, thus has one additional rule for when a year is a leap year. It will remain in synchronization with the Gregorian calendar for thousands more years, by which time one or both will have probably fallen into disuse. Similarly, Iranian calendar is also a more accurate version of the Gregorian calendar (Ross).
Formulas for computing the Julian date from the Gregorian dates are given in Danby (1988) and Sinnott (1991). Let denote the integer part (sometimes known in mathematical circles as the floor function ), let Y be the Gregorian year, M the month number (1=January, 2=February, etc.), D the day of the month, and UT the universal time. For all AD dates in the Gregorian calendar,
For the unable to see
Source here is the direct link.
http://scienceworld.wolfram.com/astronomy/
topics/CalendricalSystems.html