Because of the way we celebrate Easter Sunday, it is easy to think of Easter as a day celebration. In fact, it is an entire season of celebration. In other words, Easter isn't a day but a season.
The reason for this is reflected in Scripture. We often think Jesus was raised from the dead and that was it. In Acts 1:3, we learn that Jesus remained with the Apostles post-Resurrection for 40 days until He ascended into Heaven. This is why the Ascension is always celebrated on the Thursday 40 days after the Sunday of the Resurrection.
But the Season of Easter goes further. We continue the celebration through the Day of Pentecost, the day Acts 2:1 tells us the Apostles received the Holy Spirit. The Day of Pentecost occurs 50 days after the start of Easter, and that is what the word Pentecost actually means, 50th. The celebration of Pentecost was always 50 days after Passover, as mentioned all the way back in Leviticus. Thus we know exactly when it would have been in relation to Jesus' post-Resurrection time with the Apostles.
Easter isn't just a day to celebrate the Resurrection. It's an entire season dedicated to what the Resurrection is all about. We remember that Jesus truly was raised and spent time with the Apostles after His death and before His Ascension. We also remember that Jesus sent the Holy Spirit to guide the Apostles and those of us who have followed the Way after them even to today.