Easter isn’t just a Sunday — it’s a season. One day out of 365 is hardly sufficient to celebrate the great mystery of our faith — that Jesus Christ is risen from the dead. Accordingly, the season of Easter lasts seven weeks (a “week of weeks”), spanning the 50 days from the Sunday of the Resurrection to Pentecost Sunday and encompassing the festival of the Ascension of the Lord.

Excerpt taken from the Presbyterian Church USA website.