Why is Easter so early this year?

If the last Christmas wreath only just went into storage and there are still a few boxes of conversation hearts on hand, don't worry about wondering how another holiday managed to sneak up on us unawares.

Easter has come early on the Western Christian calendar this year.

The religious holiday's March 27 date relies on the combined wisdom of the Jewish lunar calendar, Medieval calculations, and the changing seasons, which gives the spring feast unusual variability, Caroline Wyatt wrote for the BBC. Easter has not come this early since 2008, when it fell on March 23. Although the holiday can technically occur as early as March 22, its most frequent date is April 19.

"Astronomy is absolutely at the heart of setting the date for Easter," Dr. Marek Kukula, an astronomer at the Royal Observatory Greenwich told the BBC. "It depends on two astronomical things – the spring equinox and the full moon."

The basic formula is astronomical – the Sunday following the first full moon after the spring equinox – as established by Pope Gregory XIII, founder of the Gregorian calendar. A complex history has followed the Bible's statement that Christ rose on the Sunday after Passover, and it prevents science from answering entirely this question of faith.

"The vernal equinox is fixed on March 21, despite the fact that from the years 2008 through 2101, at European longitudes it actually will occur no later than March 20," Joe Rao wrote for Space.com. "Adding additional confusion is that there is also an 'ecclesiastical' full moon, determined from ecclesiastical tables, whose date does not necessarily coincide with the 'astronomical' full moon."

The precise date of the Easter holiday is one of Christianity's great debates. All Christian sects use the same basic formula, but the Eastern sects rely on the older, Julian calendar to set the date for equinox. This results in a date that is technically more accurate by the astronomical full moon and equinox at Jerusalem, but also later than Western Christianity.

Christian leaders around the world hope they can soon eliminate theological confusion in this area at least. A movement began in the mid-20th century to try and reconcile the calendars, according to an Anglican Primate report. The Second Vatican Council in 1963 promised its consent to whatever date the Christian churches could agree on, suggesting the second Sunday in April as a useful compromise.

The last year has seen some progress on the issue. Anglican church leaders announced in January that setting an international date for Easter had made the agenda for the Primate's Meeting, Ben Quinn reported for the Guardian. Pope Tawadros II of the Coptic Christian Church in Cairo asked Archbishop of Canterbury Justin Welby during a visit the previous year, and Pope Francis and Ecumenical Patriarch Bartholomew promised their support for Pope Tawadros' plan.

"Pope Tawadros has put forward the idea to churches in the eastern tradition and the western tradition that it be fixed somewhere around the second or third Sunday of April and we will certainly be joining in," Archbishop Welby told the Guardian.

If this effort succeeds, Easter will never come so close to the heels of Valentine's Day again. Welby urged patience, however.

"I think the first attempt to do this was in the 10th century, so it may take a little while," he said, according to the Anglican report.