The NEWS! from the NAVAL OBSERVATORY, April 1988 had a good article about setting the date for Easter. The monthly newsletter always had such interesting information. If you ever wondered why the date for Easter changed over the years, their article answered your question.
They wrote: "Rules for fixing the date of Easter for the Church go back to the fourth Century AD, at the Council of Nicaea, where the church met to solve once and for all, some of its problems. Later on, in the 16th century, Pope Gregory XIII proclaimed that Easter would be ...the first Sunday following the Full Moon following the Spring Equinox. And just so there'd be no confusion, the date of the Full Moon, he said, would be derived from a set of ancient lunar tables, and the Spring Equinox he defined with a Papal Bull as being March 21st. The dates he ascribed for these events, however, do not always match the ones that are calculated astronomically. But no matter, the date of EAster is now easy to figure."
Since there is no fixed date for Easter, calendar makers may be confused at times. When Easter is celebrated, it is therefore not on one particular date. It is not celebrated on the exact date that Jesus Christ rose from the dead. Instead, as mentioned above, it is set by the date of the Spring Equinox and the Full Moon. It changes every year. Just as we celebrate Presidents Day to honor the birthdays of many presidents, it is a date which may or may not coincide with actual presidential birthdays. The day of celebrating Christmas, the 25th day of December, is also not the exact date of the birth of Jesus Christ. The celebration date of 25 December was set many years after Christ's death to coincide with a winter holiday celebrated by the Romans.
The original word Easter is derived from "Eostre." That is the name of a goddess for whom the Teutonic people had a festival every Spring.