We celebrate Holy Week and the celebration of Easter is on different dates each year. The dates are not fixed to a specific day. It can be a moveable date.
From the very beginning of the Church, the feast of the Resurrection of Our Lord was celebrated about the Jewish feast of Passover. Since the events of Christ’s Passion and resurrection occurred in that context, Christians have always felt that they should celebrate his resurrection in the same way, rather than a fixed date on the calendar.
According to the norms established by the Council of Nicaea (325) and later adopted for Western Christianity at the Synod of Whitby, Easter Sunday falls each year on the first Sunday following the first full moon after the vernal equinox.
The calculation of Easter also does not depend on the timing of the astronomical vernal equinox, which differs from year to year. Instead, March 20 is considered the “liturgical” equinox, even in those parts of the world where March signals the beginning of autumn.
The first full moon following the vernal equinox changes every year. If it falls on a Sunday, Easter must move to the next full moon. The full moon of Holy Week can fall on any day from Monday to Holy Saturday.
If you ever look up at the sky during Holy Week, you will likely see a full moon.