Question: What are the Rogation days and the Ascension?
Answer: Saint Mamertus, Fifth century bishop of Vienne in Gaul (modern day France), suffering conquest by the Burgundians, instituted the three days of supplication known as the Rogations. The Monday, Tuesday, and Wednesday before the Ascension were observed in Vienne, and later throughout Gaul as days of fasting, abstinence, and penitential processions. The observance spread throughout Europe and was adopted for the Universal Church by Pope Leo III in 816. These observances are today known as the "lesser litanies," in contrast with the "greater litanies" on April 25. In both cases the Church often marks the event with the recitation of the Litany of the Saints and a special Mass asking God to protect us from adversity and to grant us the things necessary for life in this world in preparation for eternity.
The third Rogation Day, Wednesday, is also the Vigil of the Ascension. In large churches the Vigil Mass is offered after the Hour of Sext, and the Rogations are observed with the Litany and a second Mass after None. The Vigil itself is unusually festive, with no fasting or abstinence, and Mass being offered in White vestments.
Ascension Thursday commemorated the bodily translation of our Lord into heaven on the fortieth day after His resurrection dead on Easter. It is marked with joy tempered by sadness mitigated by hope -- it is a further demonstration of our Lord's victory over sin and death; our Lord has promised to send us the Holy Ghost to be with us in His stead; but it marks the end of our Lord's days on earth until the second coming -- except, of course, for His presence in the Most Blessed Sacrament of the Altar. The Ascension is a "Holy Day of Opportunity," followed by an octave -- an entire week commemorating the feast.