1. Easter, also known as Resurrection Sunday, is a Christian festival celebrated on different dates each year. It commemorates the resurrection of Jesus Christ from the dead, as described in the New Testament of the Bible. Easter is considered the most important and oldest festival of the Christian Church.

2. The date of Easter varies each year and is determined by the lunar calendar. It falls on the first Sunday following the first full moon after the vernal equinox (the day in spring when the length of day and night are approximately equal). So, Easter can fall anytime between March 22 and April 25.

3. In Western Christianity, Easter is usually celebrated on the Sunday between March 22 and April 25. However, in Eastern Christianity, such as the Eastern Orthodox Church, Easter is determined using the Julian calendar and can fall later than in the Western Church. In some years, Easter is celebrated on different dates by both the Western and Eastern Christian churches.

4. To make the date of Easter consistent, the Gregorian calendar was introduced in 1582 by Pope Gregory XIII. This calendar accurately determines the date of the vernal equinox to ensure Easter falls around a similar time each year.

5. In summary, the date of Easter changes each year and can range from late March to late April. It falls on the first Sunday after the first full moon following the vernal equinox. The specific date of Easter varies in Western and Eastern Christianity due to different calendar systems. Overall, Easter is a significant religious festival celebrated by Christians worldwide to honor the resurrection of Jesus Christ.