Paul went back to Jerusalem fourteen years after his conversion, and various missions (at times with Barnabas) such as those in Acts 11:25–26 and 2 Corinthians 11:23–33 appear in the Book of Acts. The generally accepted scholarly estimate for the date of conversion of Paul is AD 33–36, placing the death of Jesus before this date range. Astronomical analysis Newton's method All four Gospels agree to within about a day that the crucifixion was at the time of Passover, and all four Gospels agree that Jesus died a few hours before the commencement of the Jewish Sabbath, i.e. he died before nightfall on a Friday (; ; ; ). In the official festival calendar of Judaea, as used by the priests of the temple, Passover time was specified precisely. The slaughtering of the lambs for Passover occurred between 3pm and 5pm on the 14th day of the Jewish month Nisan (corresponding to March/April). The Passover meal commenced at moonrise (necessarily a full moon) that evening, i.e., at the start of 15 Nisan (the Jewish day running from evening to evening) (; ). There is an apparent discrepancy of one day in the Gospel accounts of the crucifixion which has been the subject of considerable debate. In John's Gospel, it is stated that the day of Jesus' trial and execution was the day before Passover ( and ), Hence John places the crucifixion on 14 Nisan. Likewise the Apostle Paul, in his First Epistle to the Corinthians, implies Jesus died on a 14 Nisan ("sacrificed as a Passover lamb", ), and was resurrected on the Jewish festival of the first fruits, i.e. on a 16 Nisan (). The correct interpretation of the Synoptics is less clear. Thus some scholars believe that all 4 Gospels place the crucifixion on Friday, 14 Nisan, others believe that according to the Synoptics it occurred on Friday, 15 Nisan. The problem that then has to be solved is that of determining in which of the years of the reign of Pontius Pilate (AD 26–36) the 14th and 15th Nisan fell on a Friday. In a paper published posthumously in 1733, Isaac Newton considered only the range AD 31–36 and calculated that the Friday requirement is met only on Friday 3 April AD 33, and 23 April AD 34. The latter date can only have fallen on a Friday if an exceptional leap month had been introduced