The miracle occurs every year on the Orthodox Easter Saturday. There are many types of Orthodox Christians: Syrian, Armenian, Russian and Greek Orthodox as well as Copts. In the Holy Sepulchre Church alone there are 7 different Christian Denominations. The Orthodox Easter-date is fixed according to the Julian Calendar, and not the usual Western European Gregorian calendar, which means that their Easter normally falls on a different date than the Protestant and Catholic Easter.
Holy Fire - Photos and videos links ~ link
Holy Fire in Jerusalem - article from 1982 ~ link
Holy Fire - Holy Week and Pascha in Jerusalem - 1846 ~ link