Hello,
After the First Council of Nicaea in 325, it was decided that the calculation of the date of Easter would be based on a fixed rule[5]. Thus, Easter is celebrated on the Sunday after the 14th day of the first lunar month of spring, that is, the Sunday after the first full moon occurring during or after the spring equinox. In practice, it is simpler to go back to the origins: Easter corresponds to the first Sunday following the first full moon of spring. However, the date may vary depending on the longitude of the city where the observation is made. Catholics choose Rome.
In the end, all the churches accepted the Alexandrian method, which places the spring equinox in the Northern Hemisphere on March 21 (although the actual equinox may occur one or two days before or after that date).
A later-emerging issue is the difference in practices between Western and Orthodox churches. The former adopt the Gregorian calendar to calculate the date of Easter, while the latter still use the original Julian calendar. The Council of Bishops of the Orthodox Churches proposed a reform of the method for determining the date of Easter at a summit in Aleppo (Syria) in 1997. This reform would have eliminated the date differences between Western and Eastern churches[6]; it was to take effect in 2001, but it failed.
Calculating the date of Easter is quite complex; it is known as the computus. There are traditional tables, but also more mathematical algorithms to determine it. The first method developed by Carl Friedrich Gauss had a few errors: in 1954 (the formula gave April 25 instead of April 18) and in 1981 (April 26 instead of April 19). Many other mathematicians have since developed other formulas. See detailed calculations in the article on the calculation of the date of Easter.
Special circumstances [edit]
The two days of Easter (Sunday and Monday) are recognized as public holidays by most countries of Christian tradition, except in the United States, where Easter is celebrated only on Easter Sunday; however, Good Friday is a public holiday there. In France, for example, Easter Monday has been a public holiday since the law of March 8, 1886. In the French departments of Alsace, Guadeloupe, French Guiana, Martinique, and Moselle, Good Friday, which precedes Easter Sunday, is also a public holiday[7].
Marylena