After the Great Schism of 1054, the Catholic and Orthodox churches still believed Easter should be celebrated on the first Sunday after the first full moon to follow the vernal equinox.

• But the Catholic Church no longer found that Easter had to fall after Passover. It also switched from the Julian calendar to the Gregorian calendar, which was presented in 1582.
• The Orthodox Church still held to the original Nicean Council's formula for Easter as well as following the original calendar system of the Julian calendar.

The two churches now celebrated the same Easter holiday on two different days.

Before the invention of calendars and other modern methods of tracking years and seasons, people relied on the position of the sun in the sky and obvious signs in nature to indicate the passing of time.

When the equator and the hemispheres of the Earth became common knowledge, it was understood that the slightly tilted rotation of the earth causes different hemispheres to experience different seasons. The vernal equinox is the event that occurs in late March, which brings spring to the parts of the earth in the Northern Hemispheres.