Easter dating method
But, in the early years of Christianity, Easter dating was not accuratly defined and it was celebrated on different dates in different parts of the world. All the brethren in the East who have hitherto followed the Jewish practice will henceforth observe the custom of the Romans and of yourselves and of all of us who from ancient times have kept Easter together with you.
Based on these rules, a hypothetical first full moon in spring was calculated, called the Paschal Full Moon (PFM).The Hebrew calendar is based on the Moon, and each month starts at new moon, i.e.on the evening when the crescent is first visible (well, nowadays a computed [accurate] estimate thereof is used).This 0.25 day causes the moment of the equinox to shift forward, and when 21 March is reached, the leap day more or less resets the astronomical equinox to 20 March.The long term behaviour of the moon was described using a 19 year cycle called the moon cycle or Metonic cycle.The most complicated of calendar holidays is Easter Sunday - a "movable feast" that can occur in March or April and is determined by a complex mathematical procedure.
Easter Sunday dates are listed for calendar years 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, and are also listed for the rest of the 21st century. Easter date is a complex calculation involving the full moon and the spring (vernal) equinox. Another algorithm to determine the date of Easter Sunday is presented by the Astronomical Society of South Australia - Ronald W. The table below is a list of Easter dates that can be generated using that mathematical procedure.
Based on the astronomical knowledge of that time, some simplifications were made: The begin of spring, also called the equinox, which literally means: "equal night" (i.e.
night equal to day (length) ) was fixed on 21 March .
A correct statement is: 'Easter is the first Sunday after the first ecclesiastical full moon that occurs on or after March 21'.
For details and additional information, please see: Holiday Calendar - When is Easter Sunday ??
To keep in synchronisation with the seasons, a leap month is added approximately once every 3 years.