Easter and Astronomy

Many of our holidays have a fixed date, such as Christmas on December 25th. Others have an easily determined relative date (such as Thanksgiving on the 4th Thursday in November).

Easter is a holiday with a floating date. That date is determined by 2 astronomical phenomena: the Vernal Equinox and the full moon. We can thank the First Council of Nicaea in 325, for wanting to preserve the connection to the astronomical phenomena that occurred at the time of Christ's resurrection in 30 A.D.

Determining the exact date for Easter can seem confusing at first, but it's not nearly as complicated as it seems.

Easter is celebrated on the first Sunday after the first full moon following the Vernal (Spring) Equinox. So breaking it down into 3 steps:

-- The Vernal Equinox this year was on Wednesday, March 20th.

-- The first Full Moon after this year's Vernal Equinox was Wednesday, March 27th.

-- The first Sunday after the March 27th Full Moon is Sunday, March 31st.

The earliest Easter can occur is on March 22nd. This last occurred in the year 1818, and won't happen again until 2285.

The latest Easter can occur is April 25th. The last time that happened was in 1948, and we won't see Easter on that date again until 2038.


For a detailed discussion of Gregorian/Julian calendars, leap years, Orthodox Easter, charts, and other related topics, visit the web site of the Astronomical Society of South Australia:

www.assa.org.au/edm#Method