The Calendar Read online

  Calls for calendar reform had been increasing, however, even as the difficulties of how to accomplish this became more complicated. For instance, should the proper date for the equinox be based on the year of Caesar’s reform, the time of Christ, the Council of Nicaea or the creation of the world? What was the correct meridian on which to base the Easter calculation: Rome? Jerusalem? And what happens when the equinox falls at the end of the day in Rome and lands on the next day in the Holy Land?

  A number of astronomers tried to deal with these questions by improving the charts measuring the equinoxes to make them more accurate. None got it right, though. Indeed, as the new charts circulated, the glaring errors in the calendar became more widely known, and a persistent source of embarrassment for the Church. The wide dissemination of printed calendars, such as the oft-copied ‘Shepherd’s Calendar’, first issued in 1493, added to a sense of urgency as more people than ever used the Church’s calendar for business, governing and personal planning.

  In 1514 Pope Leo X invited the period’s greatest expert on the calendar, the Dutch astronomer, physician and bishop Paul of Middelburg (c. 1450-1533), to head up a commission on reforming the calendar. A few years earlier, in 1497, Paul had written a strident tract to the pope demanding he reform the calendar. In 1513 he wrote another impassioned tract opening with letters appealing to Leo, the Holy Roman Emperor Maximillian I, the College of Cardinals and the Lateran Council.

  As head of Leo’s new commission, Paul started by criticizing past reformers, particularly those who wanted to drop days from the year to correct the calendar’s drift. He proposed fixing the calendar not by dropping days, but by changing the date of the vernal equinox to 10 March--which he wrongly estimated to be the proper date for his time. He suggested that in the future the equinox be allowed to drift through the calendar every 134 years--this (wrong) number coming from a set of astronomic charts considered highly accurate at the time: the Alfonsine Charts, completed in 1272 by astronomers at the Castilian court of King Alfonso X (1221-1284). Paul also proposed a slight rearrangement in the lunar calendar, including dropping a day every 304 years--and the naming of lunar months after the ancient Egyptian months, to avoid using Moslem or Jewish names. The proposals were to be considered in December 1514, with the changes to be made retroactive to 1 January, 1500, when the astrologically minded Paul noted a mean conjunction of the sun and moon had occurred along the Rome meridian at noon on the first day of this important jubilee year. Surely, said Paul, this was a sign from God concerning his desire to reform the calendar.

  Leo X ordered letters dispatched in 1514 from the papal curia to all important Christian monarchs asking for opinions on the proposal from their astronomers and other experts. But only a few responded, in part because they were not given much time before the decisive meeting that December.

  The British for one did not respond, though four letters from Leo X to Henry VIII survive in the British archives, all apparently unanswered. On 21 July 1514, Leo’s first letter describes the problem and laments that ‘Jews and heretics’ were laughing at the flawed Christian calendar. Leo asked Henry to send his best astronomer or theologian to Rome, or else a written version of their views on the calendar. A year later, on 1 June 1516, the pope’s second letter complains of the poor response to the first missive, which led to the cancellation of the planned December calendar conference. He asks Henry to respond in time for the next session of the council, scheduled for later that year. Two other letters that year repeat the pope’s request, which presumably went out also to other kings who failed to answer. This lack of interest apparently doomed Paul’s effort at reform.

  One papal letter that was not ignored prompted a response from a young German-Polish astronomer then living in Frauenburg on the Baltic coast of Poland--listed as a respondent by Paul under the name Nicolaus Copernicus Warmiensis. Known as Mikolaj Kopernik in Poland, we know him by his Latinized pen name of Nicolaus Copernicus (1473-1543).

  In his early forties when the papal letter arrived, Copernicus was a canon at Frauenburg’s cathedral in this often cold, stormy coastal town near the Gulf of Danzig in what was once East Prussia. A man with a long nose, wide eyes topped by arching eyebrows and a quiet demeanour--at least this is how he looks in his self-portrait--Copernicus had settled here after years of studying and teaching at universities in Krakow, Bologna and Padua, where he had earned degrees in law and medicine. In 1500 he had travelled to Rome for the jubilee. He also met and worked in these early years with a number of leading scholars, with whom he kept in contact for the rest of his life.

  Around 1506, when Copernicus returned to the Frauenburg area, he began the astronomic studies and observations that would occupy the rest of his life. By 1512 he had written a short, unpublished manuscript outlining his early thinking about his planetary theories.* Two years later, in 1514, the pope’s missive arrived, an event alluded to by Copernicus himself in his 1543 dedication for De revolutionibus, in which he also tells us his response to the pope’s inquiry:

  *This was finally published in 1530.

  For not many years ago under Leo X when the Lateran council was considering the question of reforming the Ecclesiastical Calendar, no decision was reached, for the sole reason that the magnitude of the year and the months and the movements of the sun and moon had not yet been measured with sufficient accuracy. From that point on I gave attention to making more exact observations of these things and was encouraged to do so by that most distinguished man, Paul [of Middelburg], Lord Bishop of Fossombrone, who had been present at those deliberations.

  After Paul’s commission sputtered out, the matter of the calendar was dropped again for over 60 years during yet another tremendous upheaval in the Church: the rise of Protestantism.

  It was born during the final year of the Lateran Council, in 1517, when Martin Luther (1483-1546) tacked a document on the door of the cathedral at Wittenberg in Germany, complaining about the sale of indulgences by the Church. Luther at first did not intend to start a revolution, though he followed his act of defiance by preaching what amounted to a direct challenge against Rome. Insisting that the Bible should be the sole authority in the Church, and that salvation lay solely in faith--the first denying the pope’s authority and the second contradicting core Catholic doctrine--Luther touched a powerful nerve of discontent. In the 1520s he broke off with Rome to head up a movement that swept through Europe, attracting as many as half of all Christians in the West by the mid-century.

  This in turn incited a backlash of conservatism in the Catholic Church, and an intense counter-reformative effort by the papacy and loyal Catholic monarchs to stamp out Protestantism. It included a new Inquisition launched by Pope Paul III in 1542 and the founding of the Jesuits in 1540, in part to create religious and theological stalwarts to argue against and fight the spread of Protestantism.

  During these years of upheaval Copernicus worked quietly in Frauenburg: writing, taking astronomical observations, fulfilling his duties as a cathedral canon and tending to the occasional patient as a medical doctor of some renown.

  Apparently he lived in rooms occupying a three-storey turret set in the cathedral’s thick surrounding walls, built in the fourteenth century as a defence against the pagan-leaning Slavs. Standing high above a small freshwater lagoon just off the Gulf of Danzig, the turret gave the canon an excellent view of the shoreline, the deep-blue Baltic, and the stars. He used relatively simple astronomical instruments--an astrolabe, an armillary sphere,* and various devices to measure the altitudes of celestial objects, including the sun. Copernicus later published some of these observations in De revolutionibus. He also jotted them over the years of quiet study in his tower rooms into the flyleaves and margins of books in his library. It was in these rooms that Copernicus worked and reworked the opus that became De revolutionibus--which included attempts to properly measure and calculate the length of the year.

  *This was a concentric series of metal rings, each representing a planet’s
orbit. Arranged in a sphere, they could be used to measure and calculate planetary movements.

  Copernicus tried to fulfil his promise to Leo X by making his own fresh calculations based in part on his own sightings, and by using those made by Greek and Arab astronomers over the centuries. Summing up his findings and thoughts in De revolutioiribus, he begins a section called ‘On the Magnitude and Difference of the Solar Year’ by first explaining the difference between the two types of ‘years’ measured by astronomers.

  First is the seasonal or tropical year, which is the time it takes for the seasons to cycle through and start again. This has been the ‘year’ we have referred to throughout this book and which is the basis for our season-based calendar year. It is determined by measuring the length of time between vernal equinoxes, when the planes of the equator and the sun’s ecliptic intersect in the spring. The other year is the ‘star’ year, also called the sidereal year, which measures the time it takes for the earth to revolve around the sun back to an exact starting point in space. The difference in these two ‘years’, we now know, is about twenty minutes, with the tropical year running faster each year than the sidereal year. Known as the precession of the equinoxes, the phenomenon of a slower tropical year was first discovered by Hipparchus in ancient Alexandria, though it took until Newton for astronomers to understand its cause: gravitational pulls and tugs from the sun and moon, against an earth that is not a perfect sphere--which cause the earth’s axis to wobble slightly.

  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 flamboyan
t, 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.