The Calendar (32 page)

But Copernicus did not know this. Nor did Ptolemy in AD 139 or the Arab astronomer al-Battani in 882, whose calculations Copernicus trusted and used to compare his own observations for the tropical year:

We too made observations of the autumn equinox at Frauenburg in the year of Our Lord 1515 on the 18th day before the Kalends of October. . . . The time between our equinox and that of al-Battani there were 633 Egyptian years and 153 days and 6 3/4 hours. . . But between the observation made by Ptolemy at Alexandria, there were 1376 Egyptian years 332 days 1/2 hour . . . Therefore during the 633 years between al-Battani and us there have fallen out 4 days 22 3/4 hours, or 1 day per 128 years; but during the 1376 years after Ptolemy approximately 12 days, i.e., 1 day per 115 years.

Naturally Copernicus was perplexed by the difference between Ptolemy’s and al-Battani’s numbers, not realizing that both of their measurements were wrong. This led to an erroneous conclusion blaming the discrepancies on irregular motions of the earth that he believed affected the tropical year as measured by the equinoxes.

Still, Copernicus came up with a remarkably accurate measurement of the tropical year: 365.2425 days, or 365 days, 5 hours, 49 minutes and 29 seconds: one of the closest estimates yet to the true value (at that time) of about 365.2422 days--365 days, 5 hours, 48 minutes and 46 seconds. He also provided measurements and data that would become important four decades after the publication of his tome as Pope Gregory’s calendar commission struggled to come up with an acceptable measurement of the year.

Given the confusion over the supposed ‘irregularity’ in the tropical year, Copernicus preferred to use the sidereal measurement, which he estimated to be 365 days, 6 hours, 9 minutes and 40 seconds, or 365.25671 days. This is about 30 seconds greater than the true value. ‘But also in the case of the astral or sidereal year an error can come about,’ he admits, ‘but nevertheless a very slight one and far less than the one which we have already described’ for the tropical year.

Copernicus laboured over his opus for over 30 years but remained reluctant to publish
De revolutionibus,
knowing his sun-centred hypothesis would not be well received by traditionalists both in the Church and in academia. Indeed, for millennia humankind had assumed the earth was the centre of the universe--a theory ‘proved’ by Ptolemy and every other major astronomer, ancient and modern. To say otherwise was laughable to people of that day, even if it came from a man such as Copernicus, who was widely revered as an expert on astronomy. It took considerable persuasion by Copernicus’s friends and admirers--led by his disciple and colleague Georg Joachim Rhaticus (1514-1576)--to talk the elderly Copernicus into finally publishing
De revolutionibus.

He did so shortly before he died at age 70, but not before Copernicus added a dedication to Pope Paul III, acknowledging that his views were controversial but begging the indulgence of the Church to consider the science behind his hypothesis.

According to a friend who stood by his deathbed, the old astronomer finally got to glimpse his published masterpiece on the very day he succumbed to a months-long illness, on 24 May 1543. ‘He had lost his memory and mental vigour many days before,’ wrote this friend in a letter to Rhiiticus, ‘and he saw his completed work only at his last breath upon the day that he died.’

Despite Copernicus’s fears, his book initially attracted little controversy. Very few people could understand it, and those who did went along with a preface added to the book without Copernicus’s permission that described its contents as mere conjecture rather than probable fact. An exception was the vehement reaction of Luther and the Protestants. As biblical purists, they viewed any deviation from the scriptures as subversive, and refuted Copernicus’s sun-centred planetary system with passages in the Bible that seemed to imply that the earth stands still while the sun moves. ‘The fool wants to overturn the whole science of astronomy,’ said Luther, ‘but, according to the Scripture, Joshua bade the sun and not the earth to stand still.’*

*Luther is referring to an Old Testament story in which the Jewish prophet Joshua during a battle commanded the sun to stay in the sky.

For seventy years the Roman Church remained silent about Copernicus. Then Galileo Galilei (1564-1642) began peering in the early 1600s through his new-fangled telescope at the planets and stars, leading him to publicly endorse Copernicus’s sun-centred hypothesis in 1613--a contention that two years later led to Galileo being denounced to the Inquisition as a heretic. He cleared himself of the charge, but created such a sensation that the Church officially investigated the Copernican theory early in 1616, with Church authorities ordered to examine the fundamental Copernican assertion denying ‘that the earth is the centre of the universe and is wholly stationary’, and ‘that the sun is not the centre of the universe, and is not stationary, but moves bodily and also with a diurnal motion’. On 24 February 1616, the Qualifiers of the Holy Office concluded that a sun-centred theory was ‘foolish and absurd in philosophy, and formally heretical, inasmuch as it expressly contradicts the teachings of many passages of Holy Scriptures’.

This came at a time when the Counter-Reformation had sharply focused the Catholics towards following strict dogma. This rigidity led the Church to make a profound error when the Inquisition in 1635 forced Galileo to abjure the heliocentric theory or face torture or possible execution. As it turned out, this was one of the last great attempts by the old order of the Middle Ages to subjugate science to dogma, and the sacred to the profane.

But this came later. In the years immediately following the publication of
De revolutionibus
astronomers reading it were less interested in the sun-versus-earth debate than in studying and using Copernicus’s observations and general theories on planetary motions--including his estimates of the length of the year and his measurements of lunar phases. Indeed, the work of Copernicus, combined with other astronomic charting of the era, set the stage for two virtually forgotten men--a mathematician from Bavaria and a physician from southern Italy--and a pope named Gregory, who would finally come up with a most elegant solution to fix the calendar, and even more importantly, to enact it.

13 Solving the Riddle of Time

The patriarch has also subscribed to our calendar and admitted that it is very good. I hope that it will soon be published, because the Pope is quite eager.
Christopher Clavius, 1581

None of the three men responsible for fixing the calendar was a conqueror, notorious lover, heretic or lone monk pondering the cosmos from a cell in a monastery. They were not even particularly flamboyant, and certainly not free thinkers in the spirit of a Bacon or even a Paul of Middelburg--all of which might account for their success.

They included an obscure physician from the toe of Italy who was the genius behind the reform, a Jesuit astronomer famous for being wrong about many of his most cherished theories, and a lawyer turned pope remembered as much for his failures as for his successes. Each contributed to the reform named for one of them, and each in the story of his role offers an explanation for why the calendar was finally fixed 1,627 years after Caesar launched it, and after so many centuries of false tries and frustrations.The doctor was Aloysius Lilius (Luigi Lilio in Italian). Born about 1510 to a family of modest means, little is known about Lilius--the
‘primus auctor’
of the Gregorian reform, according to a prominent member of the calendar commission. He is said to have studied medicine and astronomy at Naples, settled in Verona, and taught at the University of Perugia before returning late in life to his home town of Ciro, in south-eastern Italy, where he concocted the solution to the calendar conundrum and designed the reforms. Indeed, if the pope had offered a prize for solving this age-old problem--as the British later offered a prize of
£
20,000 to anyone who solved the ancient puzzle of determining longitude at sea--Aloysius Lilius could have rightly claimed it. But this forgotten man never had the chance. For before his solution could be presented in 1576 to the pope’s commission in Rome, Lilius took ill and died.*

*Some accounts say Lilius died in Rome.

After Lilius’s death, his brother Antonio, also a physician acquainted with astronomy, presented Aloysius’s plan to the calendar commission. They quickly embraced it as their leading proposal, admiring it for its simplicity, elegance and avoidance of controversy. Antonio stayed on in Rome as his brother’s representative. Later he was the recipient of what passed for a discoverer’s ‘prize’ in the sixteenth century: a 1583 bull from Pope Gregory that granted him the exclusive right to publish the reformed calendar and its new rules for a period of ten years. This potentially lucrative licence was later rescinded when Antonio failed to produce enough copies fast enough to meet the demand, a delay that nearly derailed the reform.

The second prime mover was the Jesuit astronomer Christopher Clavius (1538-1612), the man behind the scenes who championed Lilius’s ideas (after an initial scepticism) and shepherded the reform through the minefields of scientific and ecclesiastic controversy before and after 1582. Until he died in 1612, Clavius worked hard to defend and explain the new calendar, ensuring that it would spread beyond the handful of countries that initially accepted it.

As a prominent public figure in Rome during the late sixteenth and early seventeenth centuries, more is known about Christopher Clavius than about Lilius. Yet little exists to flesh out who he really was. In a portrait of Clavius rendered in 1606 he is dressed in a simple Jesuit robe and a four-cornered hat. A portly, satisfied-looking man with a pudgy, bearded face, he looks sympathetic, even kind--the sort of scholar who is serious but never stuffy, smart but not precocious; one that students are fond of, and one that politicians and prelates feel comfortable assigning to commissions.

To his contemporaries Clavius was a revered sage of maths and astronomy, acclaimed as ‘the Euclid of his times’ in part because he penned a widely used translation of the original Euclid, along with several other works considered important in his day. Even the era’s greatest scientific firebrand, Galileo Galilei, came to him for validation of his telescopic observations of the moon, sun and planets. Clavius hailed them as important to astronomy, but since he was a confirmed defender of Ptolemy he disagreed with Galileo’s interpretation that craters on the moon, Venus passing through its phases, and moons around Jupiter suggested Copernicus was correct. Clavius also has the distinction of having his face inscribed on a marble relief on the base of Gregory XIII’s imposing statue in St Peter’s (probably Clavius) which shows a priest handing the pope a copy of the calendar reform.

Yet Clavius today is nearly as obscure as Aloysius Lilius. In part this comes from the bad luck to have lived between Copernicus--Clavius was five years old when
De revolutionibus
was published--and the young Galileo, who burst onto the scene in Clavius’s final years. But more than anything, Christopher Clavius is obscure because he adhered to a world view that turned out to be wrong. This made him a hero to traditionalists while he was alive, but a fool to those who came later.

Clavius was surprisingly young when Pope Gregory named him to his new calendar commission, convened in the mid-1570s. Born on 25 March 1537, in the Bavarian town of Bamberg, Clavius’s life to us is a blank page until he joined the recently formed Society of Jesus--the Jesuits--in Rome on 12 April 1555. Studying in Rome and then at the University of Coimbra in Portugal, Clavius returned to Rome in the early 1560s to finish his education and then to teach at the Jesuits’ own Collegio Romano, where he became a professor of mathematics. But for a few short trips, he would remain in Rome until his death.

As a mathematician and astronomer, Clavius was a minor figure, notable mostly for his work on Euclid, algebraic notation and the calendar--and for his staunch defence of an earth-centred universe. Yet Clavius was flexible enough to constantly update his own theories to incorporate Copernican data and Galileo’s observations, attempting to squeeze it into an increasingly strained Ptolemaic interpretation.