Jesuit Astronomer Christopher Clavius Helps To Fix The Date Of Easter

Arkansas City prepares for Easter
By Foss Farrar
No specific date exists for Easter -- unlike just about any other holiday that comes to mind. Its date changes from year to year, based on complex calculations involving events of the heavenly bodies. This year's date of March 23 is about as early as Easter can occur, according to a local astronomy teacher and sources on the Internet. "The earliest it can occur is March 19; it's not going to do that again for a long time," said Cowley College astronomy instructor Todd Shepherd.

The last time Easter fell as early as March 23 was in 1913, and it won't fall that early again until 2160, Shepherd said on Friday. That's 152 years, more than a lifetime away, he added.

Complex calculations dating back many centuries are used to figure the date of Easter, said Shepherd. Back then, the Roman Catholic Church came up with a "Paschal full moons" estimate. "Their estimate did not necessarily match up with the actual full moon," he said. Shepherd said he doesn't bother to discuss details of all this to his students. Instead, he teaches a simple rule that he says works 99.1 percent of the time. "Easter falls on the first Sunday after the first full moon after the vernal equinox," Shepherd said. "That's as deep as I go because it gets very complicated." Thus, Easter's date depends on the relationship between a solar and a lunar event. And this year, the two events are occurring very close together, he said. The date of the vernal equinox -- the first day of spring -- can vary from March 19 to 22, he said. "This year, the first day of spring was on March 20; the first full moon following is this evening, March 21," he said. "So the Sunday after, Easter, will be March 23." The reason for all the computation by church authorities is that the Gregorian Calendar that serves as a standard for the world doesn't match up with the cycles of the moon, according to Internet sources."

The current Gregorian ecclesiastical rules that determine the date of Easter trace back to 325 CE at the First Council of Nicaea convened by the Roman Emperor Constantine," according to a Web site of the U.S. Naval Observatory.

"At that time the Roman world used the Julian Calendar." Julius Caesar put that calendar into place.

The Rev. Charles Seiwert, pastor of Sacred Heart Catholic Church, said he'd leave detailed explanations of how the Easter dates are figured to "a Jesuit astronomer." ( Christopher Clavius )

But he offered a simpler explanation: "It very much followed the Jewish holiday of Passover and the seder meal that accompanied it. The church followed that timing." He said he was pleased that even though Easter comes early this year, the weather in south-central Kansas looks nice for Sunday. "We are extremely fortunate we didn't have cold, snowy weather in mid-March -- or flooding, like the state next to us," Seiwert said. "That means people can get out easily on Sunday for sunrise services."

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