That’s why the Vatican of the day paid for the astronomical research that also confirmed Galileo, whom the church was persecuting at the time, had been right.
Fleisch will flesh out that story at 7 p.m. Sunday when he presents “The Church in Renaissance Astronomy.” The program in Room 319 of the Barbara Deer Kuss Science Center is free and open to the public.
Fleisch said he stumbled across the story in a bookstore in Cambridge, England, during his 2005 sabbatical leave.
There he found “The Sun and the Church,” a book that detailed church astronomers’ attempts to more precisely measure two things needed to predict when Easter would fall: the lengths of the solar year and the lunar month.
Astronomers knew the solar year was about 365¼ days long and the space between full moons was about 29.5 days.
“But they were having trouble with their decimals,” Fleisch said.
The precise numbers turned out to be 365.2433 days in the solar year and 29.5 days for the lunar month. To get closer to those precise numbers, Fleisch said, the church adapted some of its cathedrals to be astronomical observatories.
The first step was to bore a hole high in the cathedral that would project a thin ray of light to the floor below. On that floor, they then drew what’s called a meridian line.
Just as the equator is an imaginary line stretching around the center of the earth, a meridian is a line that circles the earth from top to bottom. Not by coincidence, meridian lines are used to divide the earth into time zones.
With a small segment of that north-south line on the cathedral floor, astronomers tracked and recorded where the sunlight fell on it year after year after year.
Each day, that same line told them when it was noon local time.
Fleisch said some cathedrals’ meridian lines were works of art — strips of bronze inlaid in white marble for up to 120 feet.
Through their studies, “they refined their estimate of how long a year was,” Fleisch said, and “put more decimals” into their calculations.
While on sabbatical in Europe, Fleisch visited two cathedral/observatories: Santa Maria degli Angeli in Rome and St. Sulpice in Paris.
He said the Roman site had an interesting wrinkle: The cathedral was built on the site of an old Roman bath, a symbol of what the church saw as the hedonistic culture it had replaced.
Because its foundations had long since settled into place, the building also made a reliable observing device. Cathedrals also were suited for observatories because of their height.
Fleisch said the Easter tracking project that began in the 1630s and continued for nearly 200 years produced astronomy “every bit as good as Galileo’s.”
The astronomers not only measured the length of the solar year to within one second — “and this was 1703,” Fleish said — but their work ultimately proved Galileo right in claiming that the sun, not the earth, was the center of the solar system.
Fleisch said in its search for Easter, the church was “supporting the development of astronomy in full.
“In those days, you didn’t have the National Science Foundation,” he said.
The astronomers also left what Fleisch calls “a little post card” for researchers that followed.
While researching Easter, they observed that he pole star (Polaris or the North Star) is not a fixed point in the sky, as so many had assumed.
“Every day it makes a little circle around the true pole,” Fleisch said.
Checking their observations, they “predicted where the pole would be (to the year) 2500,” Fleisch said. “This was astounding to me.”
“They put it in the floor of the church, and we can check it today,” he said.
Or on any Easter.
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