Fast approaching are the three minor Rogation Days (the Major Rogation fell on April 25) held on the Monday, Tuesday, and Wednesday immediately before Ascension Thursday. Like the Ember Days, these are days set aside to observe a change in the seasons. Rogation Days are tied to the spring planting.
As the Catholic Encyclopedia notes, Rogation Days are "Days of prayer, and formerly also of fasting, instituted by the Church to appease God's anger at man's transgressions, to ask protection in calamities, and to obtain a good and bountiful harvest."
Rogation is simply an English form of the Latin rogatio, which comes from the verb rogare, which means "to ask." The primary purpose of the Rogation Days is to ask God to bless the fields and the parish (the geographic area) that they fall in. The Major Rogation likely replaced the Roman feast of Robigalia, on which (the Catholic Encyclopedia notes) "the heathens held processions and supplications to their gods." Since the practice itself was laudatory, just misdirected, Christians adopted it as their own. By the time of Pope St. Gregory the Great (540-604), it was already considered an ancient custom.