The Jewish Passover celebrations began yesterday. The Passover commemorates God’s gift of saving their firstborn while the Egyptian firstborn were struck down in the plague. This Passover, in synagogues all over the world, the first born sons of Jews will recite thanks to God for saving their kind. It is an incredible tradition.

The Passover lasts seven days. At the end of those seven days in Biblical times the Romans crucified Jesus Christ. The Jews base the dates of Passover on their calendar which is lunisolar, or semi- lunar. They have an intercalary month which takes place seven times in 19 years; this is called the Metonic cycle, after the Greek astronomer Meton, who proposed it about 432 B.C. to express the relation between a lunar and solar year. The Jewish Diaspora traditionally added an extra day to their Passover just to be safe, in case the local calendar was wrong.

The early Christians based their calendar on the same lunisolar system which was integrated into the Julian Calendar, named after Julius Caesar and which ruled time from 45 B.C until 1582 A.D.. This calendar was not astronomically correct in that although it had a leap year, the actual variance was slightly less than the six hours per year that the Emperor calculated. So in fact as time progressed the calendar was being thrown out of pace.

The Gregorian calendar was adopted by the Western World in 1582, when by the political plotting and the use of the Julian Calendar Easter was falling too early in March. The principle of calculating this Spring Festival was, and still is, based, on the vernal equinox that occurs in March. Vernal implies spring (as it would be in the northern hemisphere) and the equinox is an astronomical description for that time of year when the sun is perpendicular to the equator. Easter is calculated on the first Sunday after full moon after the vernal equinox. The Orthodox Easter has to fall at the end of the Passover, which is historically correct. More importantly, the Gregorian calendar has fixed the vernal equinox on 21 March, when in fact it varies astronomically by a day each way. In addition, the Gregorian calendar uses an “ecclesiastical” full moon, and not the astronomical full moon in the calculation.

So this year the Orthodox Easter and the Catholic Easter should coincide by virtue of the moon and the vernal equinox, but in fact the Orthodox Easter is delayed by one week to fall at the end of the Passover.

Greece remained true to her stubborn nature in that she was the last to adopt the Gregorian calendar, as late as 1928, after the population exchange destroyed the Levant. The yellow beast, China, only adopted the Gregorian calendar in 1949.

It is a fascinating moveable feast, the Jewish Passover and the Christian Easter. The one Christian church follows the Jewish rite, while the other has chosen to rule the astronomical calendar with an average day, 21 March and an arbitrary full moon. The Jewish word for the Passover is pesach. The Greek word for Easter is pascha. Not too dissimilar in sound?