A practical, if imperfect unity
In the northern hemisphere, the Week of Prayer for Christian Unity is celebrated from January 18-25, while the southern hemisphere observes the ecumenical event around the time of Pentecost.
In Jerusalem, it begins on the first Saturday after January 19. Thus, this year's Christian Unity Octave will be observed in the Holy City from January 25-February 2.
WHY IS THE DIFFERENCE?
It is to respect the Armenian Apostolic Church, which celebrates Christmas on the night of 18-19 January, according to the Julian calendar.