The Spring Equinox occurrs on the 20th March when night and day are of equal length, winter comes to an end and spring arrive.
The Jewish Passover is calculated according to lunar cycles and must fall on the night of the first full moon following the Spring Equinox. This was the 30th March.
The Resurrection of Christ is believed to have occurred three days after the Passover meal. But tradition has it that the Resurrection occurred on a Sunday. Christians therefore prefer to celebrate Easter on the first Sunday after the first full moon following the Spring Equinox. So Easter this year falls on the 4th April.
Sometimes, it should happen that Passover and Easter fall on the same day, when the first full moon after the Spring Equinox occurs on a Sunday.
The early Christians, however, wished to differentiate themselves from the Jews and agreed at the first universal Council of the Church at Nicea in 325 AD that if the first full moon after the Spring Equinox falls on a Sunday, Easter should be postponed to the following Sunday. Passover and Easter, therefore, can never fall on the same day.
In some years, both Western and Eastern Christians celebrate Easter on the same day, but this is not always the case because Eastern Christians hold to the letter of the Council of Nicea that states that the Spring Equinox occurs on the 21st March, though in the 17 centuries that have lapsed since the Council, the date of the Spring Equinox has slipped back through the year. This is the case even more than at first appears, since the Eastern calendar is that of Julius Caesar which is 13 days behind the Western calendar, introduced in the 16th Century by Pope Gregory the Great.
The shift in the Spring Equinox is due to a wobble in the Earth’s spin that takes 24 000 year to complete. The sun is currently in the constellation of Pisces during the Spring Equinox, but in Roman times it was in Aries, and in 600 years times it will be in Aquarius, which will bring in “the dawning of the Age of Aquarius”.
Or, to continue, “When the Moon is in the seventh house, and Jupiter aligns with Mars. Then peace will guide the planets, and love will steer the stars.”,
Have a happy Easter!
This blog first appeared as a story for the Cairo BCA Magazine in April, 2010, to promote astronomy in Sinai with an 8″ Meade LX90 Telescope.