The difference between the dates of Roman Catholic Easter and Eastern Orthodox Easter arises from the use of different calendars to calculate the date of the feast. The primary calendars involved are the Gregorian calendar and the Julian calendar.

1. Roman Catholic Easter (Western Christianity):

   • The Roman Catholic Church, along with most Western Christian denominations, follows the Gregorian calendar for calculating the date of Easter.
   • The Gregorian calendar, introduced by Pope Gregory XIII in 1582, is a more accurate solar calendar than the Julian calendar.
   • Easter in Western Christianity falls on the first Sunday after the first full moon on or after the vernal equinox (around March 21).

2. Eastern Orthodox Easter (Eastern Christianity):

   • The Eastern Orthodox Church, along with some other Eastern Christian churches, follows the Julian calendar for liturgical purposes.
   • The Julian calendar, introduced by Julius Caesar in 45 BCE, is less accurate than the Gregorian calendar, especially in its calculation of leap years.
   • Orthodox Easter is calculated using a similar method as in the West but using the Julian calendar for the vernal equinox and the full moon.
   • As a result, Eastern Orthodox Easter often falls later than Western Easter, and there can be instances where the two celebrations are on the same day or are separated by several weeks.

The difference in the calendar systems and their calculations means that the two branches of Christianity may celebrate Easter on different dates. Occasionally, there are years when the celebrations coincide, but this is not the norm.

Efforts to address the issue and establish a common date for Easter have been ongoing, but achieving consensus has proven challenging. Some discussions involve adopting a fixed date for Easter, while others explore methods for reconciling the differences in the calculation of the date. Despite these discussions, as of my last knowledge update in January 2022, no universal agreement had been reached on a common date for Easter across all Christian traditions.