Good Friday 

Good Friday is the "culprit" for the differences in church calendars

Pope Gregory XIII on 24 February 1582 issued a bull called inter gravissimas. This document established the Gregorian calendar. The origin of the need for reform of the Julian calendar was - the date of Good Friday and Easter.

Good Friday is measured as the Friday of the week of the first full moon after the vernal equinox. However, due to the nature of the Julian calendar, equinox in Grgurevo weather moved in ten days from the time of the Council of Nicaea in 325 CE. Therefore, Gregory eliminate ten days of the new calendar, and 4 October 1582 was followed by the fifteenth, which was restored Equinox 21st March next year.

Since the Orthodox Church did not accept the new calendar, the dates of the celebration today of Good Friday and Easter among churches rarely coincide.

source: http://elementarium.cpn.rs/teleskop/veliki-petak/

More about our customs:

Egg tapping
Egg decorating