We can always expect the Solemnity of the Assumption of the Blessed Virgin Mary to come on Aug. 15 and the Optional Memorial of St. Patrick on March 17. But many feast days of the Church year are not settled on one particular date of the calendar. These are known as moveable feasts. Their dates are bumped ahead (or back) on the calendar depending — in most cases — on that most important moveable feast of all: Easter. See how much you know about them.