Q: How do they determine which day Easter falls on each year?
A: According to an online The Old Farmer’s Almanac article, Easter is celebrated on the first Sunday following the full moon that occurs on or just after the spring equinox. Easter commemorates Jesus Christ’s resurrection from the dead after his crucifixion and does not have a fixed date.
Easter 2021 will be observed on Sunday, April 4. Eastern Orthodox Easter (most Eastern Orthodox churches use the Julian calendar to determine the dates of movable feasts such as Easter) will take place on Sunday, May 2.
“This Easter is just one week after March’s full Moon (Sunday, March 28), which is the first full Moon to occur after the spring equinox (March 20, 2021) and is therefore known in the Christian calendar as the ‘Paschal Full Moon,’” according to the online article.
“Over a 500-year period (from 1600 to 2099 AD), it just so happens that Easter will have most often been celebrated on either March 31 or April 16,” according to the article. “Many Eastern Orthodox churches follow the Julian calendar rather than the Gregorian. In this case, the observance of Easter can occur between April 4 and May 8.”
The Julian calendar was a dating system established by Julius Caesar about 46 BC. The Gregorian calendar, also known as the Western or Christian calendar, was introduced in 1582 by Pope Gregory XIII to more accurately calculate leap years based on the actual time it takes the Earth to circle once around the sun.