{"id":32862,"date":"2022-01-17T21:01:48","date_gmt":"2022-01-17T21:01:48","guid":{"rendered":"https:\/\/www.roger-pearse.com\/weblog\/?p=32862"},"modified":"2022-01-17T21:01:48","modified_gmt":"2022-01-17T21:01:48","slug":"a-brief-yet-very-nice-description-of-the-calculation-of-the-date-of-easter-from-a-php-manual","status":"publish","type":"post","link":"https:\/\/roger-pearse.com\/weblog\/2022\/01\/17\/a-brief-yet-very-nice-description-of-the-calculation-of-the-date-of-easter-from-a-php-manual\/","title":{"rendered":"A brief yet very nice description of the calculation of the date of Easter from … a PHP manual!"},"content":{"rendered":"

Computer programs need to calculate the date of Easter sometimes.\u00a0 In the PHP programming language, there is a function, easter_date<\/strong>, which is used for the purpose.\u00a0 The manual page is here<\/a>, and is really rather good!<\/p>\n

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The date of Easter Day was defined by the Council of Nicaea in AD325 as the Sunday after the first full moon which falls on or after the Spring Equinox. The Equinox is assumed to always fall on 21st March, so the calculation reduces to determining the date of the full moon and the date of the following Sunday. The algorithm used here was introduced around the year 532 by Dionysius Exiguus. Under the Julian Calendar (for years before 1753) a simple 19-year cycle is used to track the phases of the Moon. Under the Gregorian Calendar (for years after 1753 – devised by Clavius and Lilius, and introduced by Pope Gregory XIII in October 1582, and into Britain and its then colonies in September 1752) two correction factors are added to make the cycle more accurate.<\/p>\n<\/blockquote>\n

Well, we’ve all seen very much worse explanations than that!<\/p>\n