Religions adjust timetables to keep holidays in sync with Earth’s orbit

This is a leap year, with an extra day on the calendar next week to tidy up the minutes that piled up uncounted for the past four years. The mathematical housekeeping is necessary because it really takes the earth more than 365 days to orbit the sun.

That extra day affects the date that Christians will celebrate Easter this year.

Meanwhile, there's a whole leap month running on the Jewish calendar. It's a corrective measure that occurs every three years or so to put the 29-day monthly lunar calendar in sync with the solar calendar. A Jewish religious leader came up with this formula in the fourth century as a way to ensure that Passover is always celebrated in the spring, as it was in the first place.

Last year the serendipity of calendar computations set Christians and Jews to celebrate their holy days in the first week of April. This year Easter is really early, and the Passover is relatively late.

March 23 is a rare early date for Easter. The last calendar with a March 23 Easter on it was in 1913. The next time it will occur is 2160, according the Earth & Sky Web page.

The formula for setting the holy day was established at a fourth-century church summit, the first time geographic branches of the spreading religious movement got together to regularize what they believed and decide when to mark their greatest holy day, celebrating the resurrection of Christ.

The formula the Council of Nicea came up with: Easter will be the first Sunday after the first full moon after the spring equinox.

This year that's March 20 equinox plus March 21 full moon.

As we all know, the equinox occurs halfway between the shortest and longest days of the year; it's a day when night and day are equal. It happens again in the fall, important to druids but irrelevant in this story.

This year the spring equinox is early. It's usually calculated to be on March 21. But with an extra day on the leap year calendar, the timing was skewed.

Orthodox Christians have a long wait for Easter -- they will celebrate on April 27. They use the Julian calendar, which sets March 21 as the fixed date of the equinox. Plus, they have a centuries-old tradition of waiting until after Passover. Last year they celebrated Easter on the same date as Western Christians.

Jews will begin the seven-day observance of Passover on April 20, 17 days later than last year. One of the major holy days of the faith, it commemorates the liberation of the Hebrew people from slavery in Egypt. Passover, or Pesach, begins with the full moon on day 15 of Nisan, first month of the Hebrew lunar calendar.

Jews are accustomed to it being a movable feast. "We are living in a world that does not revolve around the Jewish calendar, so it does present a variety of challenges," said Rabbi Peter Schaktman, of Temple Emanu-El. Children might have school holidays linked to the Christian season, and "a lot of things go on hiatus during the Easter season, people are not available for meetings, offices are closed."

"Most of the Jewish holidays are tied to seasonal events. They have an agricultural meaning and a historical significance," Schaktman said. "What they demonstrate is the ongoing connection with the land of Israel. They are tied to the seasons in Israel."

It's intriguing to imagine what went on in the minds of the fourth-century leaders from both religions who used advanced math and astronomy to affect -- or should we say dictate -- how people would keep the faith centuries later.

And it's even more intriguing to fantasize about what Easter sunrise March 23, 2160, will bring.

Mary Adamski covers religion for the Star-Bulletin. Reach her at madamski@starbulletin.com.