Which day is the Sabbath day?

Saturday is the Sabbath as determined by the Old Testament. Very early Christians began to celebrate Sunday because it was the day Jesus rose from the dead.I am a Catholic priest. The Catholic church has celebrated Mass(Eucharist) on Sunday because it is closely linked to Christ's Resurection. The Mass today , as it is celebrated- is closely linked to Jesus death and resurection. Seventh Dday Adventists and Seventh Day Baptists do observe Saturday . Other Christian bodies do not and worship the Lord's Day as Cathoic's do-- on Sunday. I would never argue the point with those who believe it should be Saturday. If one feels strongly that the day to worship is Saturday- then do it. I ahve been a priest for over 25 yrs and no one has ever had a problem with Sunday-- so I do not beleive it is a problem with the vast majority of Christians.