Ascension Day is celebrated on the 40th day of Easter, 39 days after Easter Sunday. The feast is intended to recall the statement that Jesus, with the Ascension, now sits "at the right hand of God", as it says in the New Testament.
It is the counterpart to the 40-day fasting period, which is also known as the Lenten period. The holiday has a religious origin, but was only established as a counterpart to Mother's Day in the 19th century.