LONDON (RNS) A top British scientist claims his biblical, historical and astronomical research shows Christians have been observing Jesus’ Last Supper on the wrong day of the week.

Cambridge University Professor Colin Humphreys says Jesus’ final meal with his disciples actually was eaten on the Wednesday before the Crucifixion — one day earlier than has been traditionally accepted.

The mix-up, Humphreys concludes in his new book, “The Mystery of the Last Supper,” may be because Jesus and disciples Matthew, Mark and Luke used one calendar, but fellow disciple John used another.

Humphreys notes the Gospels attributed to the first three claimed the last meal coincided with the Jewish Passover, whereas John’s Gospel says the meal took place “before” Passover.

Eminent biblical scholar F.F. Bruce once described that contradiction as “the thorniest problem in the New Testament,” but Humphreys said, “if we use science and the Gospels hand in hand, we can actually prove that there was no contradiction.”

Humphreys theorizes that Jesus employed an age-old Jewish calendar — perhaps dating back to the Exodus from Egypt — rather than the official lunar calendar popular at the time.

That, Humphreys said, would put the Passover and Last Supper meals on the Wednesday rather than Thursday, and means Jesus’ arrest, interrogation and trials were not all crammed into a single night but were instead spread over a longer period of time.

Humphreys based his project on earlier research he conducted with Oxford University astrophysicist Graeme Waddington 28 years ago, which established the date of the Crucifixion as Friday morning, April 3, 33 A.D.