I'm often asked, "Why are there two Easter celebrations?" There's a simple explanation, but complicated interpretations.

Here's a very quick History 101 primer: in Christianity, you have the Western Christian Churches (Catholic, Protestant and smaller denominations) and the Eastern Orthodox Churches (Greek, Russian, Lebanese, and many others). The formula for Easter, the first Sunday after the first full moon on or after the vernal equinox, is identical for both Western and Eastern Easters, but the churches base the dates on different calendars. Western churches use the Gregorian calendar, and the Orthodox churches use the older Julian calendar.

That much is clear cut, but the rest of it is Byzantine, no pun intended. The two churches do not agree on the definition of the vernal equinox and the full moon. The Eastern Church sets the date of Easter according to the actual, astronomical full moon and the actual equinox as observed along the meridian of Jerusalem, site of the Crucifixion and Resurrection.

The Western Church does not use the actual or astronomically correct date for the vernal equinox, but a fixed date, March 21. And by full moon, it doesn't mean the actual astronomical full moon, but the "ecclesiastical moon," which is based on tables created by the church. This allows the date of Easter to be calculated in advance rather than determined by actual astronomical observances.

The Eastern Church also maintains that Easter always falls after Passover, since the Crucifixion and Resurrection of Christ took place after he entered Jerusalem to celebrate Passover. In the Western Church, Easter sometimes precedes Passover by weeks.

Whether you observe Easter or Passover, or neither, may you and your loved ones have a blessed season.

Phil Paleologos is the host of The Phil Paleologos Show on 1420 WBSM New Bedford. He can be heard weekdays from 6 a.m. to 10 a.m. Contact him at phil@wbsm.com and follow him on Twitter @PhilPaleologos. The opinions expressed in this commentary are solely those of the author.