The Fortieth Day and Why It Always Falls on a Thursday

Ascension Day falls thirty nine days after Easter by the count this rule records, which places it, counting Easter Sunday itself as day one, on the fortieth day of Eastertide, always a Thursday given Easter's own fixed position on a Sunday. The date's basis is a specific detail in the Acts of the Apostles, which states that the risen Jesus appeared to his followers over a period of forty days before his ascension into heaven, a span the Gospel of Luke, traditionally attributed to the same author as Acts, treats more compactly without the same explicit forty day interval.

The forty day figure carries an echo the Western liturgical tradition treats as deliberate rather than coincidental, paralleling the forty days Jesus is described fasting in the wilderness at the start of his ministry and the forty days of Lent that Western practice keeps before Easter, so the same number marks the season's opening penitential period and, symmetrically, the interval before the ascension that closes the Easter season's central narrative. Ascension Day's Thursday position, unusual for a major feast in traditions where Sunday observance is otherwise the norm, follows directly and unavoidably from the forty day count itself.