1. What is the year 1975 on the religious calendar of the Roman Catholic Church, and how often are such celebrations held?

1975 of our Common Era​—the year marked in the religious calendar of the Roman Catholic Church for celebration as a Holy Year, which really began on Christmas Eve, December 24, of the year 1974.

2. Current statistics show what as to the size of Christendom?

² The Roman Catholic Church entered the Holy Year for 1975 with an estimated Roman Catholic population of 551,949,000, making it the largest religious organization on earth today.