The Synaxarion readings we use at my church during Holy Week have one feature that strikes me as very odd: they assign Roman calendar dates to the days of the week of Christ's death and resurrection. Last night at Bridegroom Matins, for example, the Synaxarion that I read to the congregation said that the day when Judas agreed to betray Jesus was Wednesday, which corresponded to 21 March. Counting forward, this implies that the Crucifixion occurred on the 23rd, and the Resurrection occurred on the 25th. I have been unable to track down the source of this chronology.
I am aware of two dates that were assigned to the Crucifixion by early Christians. The first was 6 April. Later on, for some reason, this date was displaced by 25 March. (It is no mere coincidence that these dates precede Theophany and Christmas, respectively, by nine months, but the dates of those feasts were based on the date of the Christ's death, not vice versa. I'll skip that tangent for now and save it for a separate post in December.)
Modern scholars have attempted to determine the date of the Crucifixion by reconstructing the Jewish lunar calendar for the range of years in which Christ might have died. Following Luke 3:1-2, which places the beginning of Christ's ministry with respect to the reigns of Tiberius Caesar, Pontius Pilate, Herod Antipas, Philip, and Lysanias, the range of plausible years can be narrowed to AD 29-36. In addition, St. Paul's conversion is usually dated to AD 34, which restricts the range further. Then it becomes a matter of extrapolating the lunar cycles backwards to the first century and seeing which years, if any, fit the chronology presented in the gospels. In performing these calculations, allowance must be made for the imprecision of Jewish reckoning. Sometimes the month might have begun a day after the new moon if the moon was not visible, and occasionally an error might be made in determining when to add an intercalary month (a 13th month to keep the lunar calendar in sync with the solar calendar) at the end of the year.
One complication is that the gospels present two different chronologies of Holy Week. The Synoptic gospels, which present the Last Supper as a Seder meal, imply that Jesus was crucified on the first day of Passover, 15 Nisan. John, however, tells us that Jesus was crucified on the day before Passover, 14 Nisan. So both chronologies must be considered.
The first person to do these calculations was Sir Isaac Newton, in 1733. Newton narrowed the dates down to 3 April 33 and 23 April 34. He then chose the latter date based on a correspondence between the grain-plucking episode from the gospels (Mark 2:23) and his understanding of the growing season for grain. However, his selection of AD 34 was based on rules of the Jewish calendar that were not yet in effect in the first century. Therefore, Newton's work was not taken very seriously.
Scholars of the 20th century returned to this question. They settled on two plausible dates: 7 April 30 and 3 April 33. Note that both dates correspond to 14 Nisan, and are thus consistent with John's chronology, not with the Synoptics.
For many years, AD 30 was the consensus favorite. I suspect there were two reasons for this. First, it had become accepted the Christ was born in 6-4 BC. Many people were attached to the notion that Christ had died at the age of 33. If he had died in AD 33, that would have made him nearly 36-38. Therefore the earlier Crucifixion date was favored. Second, based on the erroneous belief that Christ was born in AD 1, in conjunction with the idea that he died at age 33, it was popularly believed that Christ was crucified in AD 33. Scholars tend to enjoy the feeling of superiority that comes from dismissing such popular beliefs. (I'm not sure why they did not think, rather, to question the death-at-age-33 theory . . .)
In the last decade, however, the consensus has shifted with near unanimity to AD 33 as the year of the Crucifixion. In AD 30, Christ's ministry was still in its early stages. AD 33 has astronomy, history, and tradition going for it.
In addition, further astronomical research has found that there was a lunar eclipse on 3 April 33. This is consistent with Peter's quotation from Joel (Acts 2:20): "The sun shall be turned into darkness and the moon into blood." In addition, the late-second-century apocryphal Report of Pilate to the Emperor Claudius claims that at the Crucifixion "the moon appeared like blood." This was a common description of lunar eclipses in that era, and it might very well record a memory of an eclipse on the day of the Crucifixion. This is the icing on the cake for AD 33.
Unless something forces us to make a radical re-evaluation of the era in which Christ lived or the correspondence of the days of his death and resurrection to the Jewish Passover, the consensus in favor of 3 April 33 is unlikely to change. In the meantime, I will continue to try to get to the bottom of the dates in the Synaxarion.