What is Time? Gregorian Calendar, These Fantastic Worlds
What is Time? The Gregorian Calendar

What is Time? The Gregorian Calendar

From 1540, two major developments brought long-lasting change to our notions of time. The calendar reforms of Pope Gregory gave us the Gregorian calendar we have today, and the ultimate acceptance of the heliocentric system (that the earth circulated the sun, not the other way round) provided a victory for science over the Catholic Church.

Copernicus’ Radical Idea

Polish astronomer and monk Nicolaus Copernicus (1473–1543) used his knowledge of recent mathematical advances in Western understanding to predict the motion of the planets more accurately. He concluded that the earth and the planets must revolve around the sun. He was reluctant to publish his findings for fear of the criticism his theories might generate from astronomers and from the Catholic Church. It was, however, over 70 years after his death that the Church first condemned his work.

Heliocentric System, Gregorian CalendarFor centuries this heliocentric system had been known to scholars in the East and to some in Europe, but the Church based its worship on the fact of God creating the earth and therefore explicitly making our planet the centre of the universe. This was supported by Christian philosophers who adopted ancient Greek Aristotelian and Ptolomeic concepts of the sun and the universe revolving around the almighty earth (the geocentric system). Any threat to this was deemed heretical. Galileo Galilei (1564–1642), the celebrated Italian astronomer and mathematician, initially supported Copernicus’s work, but was forced to recant in 1633 in one of the last great efforts of the Grand Inquisition to halt the march of scientific progress.

The Triumph of Science

After the discoveries of Copernicus, the German astronomer Johannes Kepler (1571–1630), with his important work on the elliptical planetary orbits, and Galileo’s telescopic observations generated much work on the motion of planets through to Isaac Newton (1642–1727), who established the fundamental concept of gravity and formed the basis of modern scientific observation.

Copernicus’s calculations in his De Revolutionibus demonstrated how far the West had finally assimilated the knowledge of the East. He showed, for instance, the solar year to be 365.2425 days long, only 35 seconds out by our current reckoning. At last, Europe finally recovered from the fall of Rome, some 1200 years before, having lost in the Dark Ages, the knowledge inherited from the ancient Egyptian, Greek, Sumerian and Indian civilisations. Observations of differences between the lunar, sidereal and solar year had become increasingly obvious, and could now be resolved.

Pope Gregory, Gregorian CalendarPope Gregory

So, the Church, in the form of Pope Gregory XIII (1502–85) acknowledged that the cumulative errors of Julian calendar (Easter, Christmas, Saint’s days) undermined its authority. Since the 1450s, printed calendars had been distributed to anyone who wished to use them, using the new technology of printing on paper, putting further pressure on the Church to be accurate. Pope Gregory set up a calendar commission, consulted widely with church and state authorities and eventually published his Papal Bull of 1582 which transformed the official calendar.

Core Gregorian Reforms

  • New Year’s Day was established as 1 January.
  • Ten days were to be lost, 5–14 October.
  • Leap days were to be inserted after 28 February every four years, except those divisible by 100, but not 400 (i.e. 1900 was not a leap year, but 2000 is).
  • Easter dates were recalculated against a complicated formula which compensated for differences between the solar, sidereal and lunar years, the different observations of which had originally prompted the gathering call for change.

Acceptance and Denial

It took nearly 400 years for the Gregorian calendar to be accepted throughout the Christian world, and the story of its acceptance reflects the continuing conflicts of faith within the Christianity and the political machinations of its secular partners.

Most Catholic countries adopted the reforms within the first year, although a further order had to be issued suspending days in February.

  • In the first wave were France, Italy, Spain, Portugal, Poland and Luxembourg, followed by Sweden, Bavaria and Austria.
  • The Netherlands, Belgium and Catholic Germany agreed in 1584, Hungary in 1587.
  • Other countries followed at a very different pace: United Kingdom 1752, Japan 1873, Egypt 1875, Eastern Europe 1912–19, including Russia in 1918.
  • China adopted it in 1912, but it took the overthrow of the Nationalist government by Mao Zedong in 1949 to enforce countrywide change.


In the first years, while Catholic states accepted the changes the Protestant countries, such as Britain and much of Germany, took much longer to agree to the need for change. This was because the Catholic pope was seen as trying to exert his authority over the whole Christian community after the splits of the Reformation.

This prolonged process of adoption and rejection led, in England, to two centuries of parallel calendar notations, with letters and documents recording ‘Old Style’ (OS) and ‘New Style’ (NS).

New Year’s Day was also erratically enforced throughout the Christian world with 1 March, 25 March and 25 December also being used. This all changed, though, by the time the last major European power, Britain, finally joined the Gregorian scheme in September 1752, bringing, with it the colonies, especially the increasingly influential North America.

The English Mob

Voltaire’s famous jibe, that ‘the English mob preferred their calendar to disagree with the sun, than agree with the Pope’ was entirely accurate. Although the English court, since the brief reign of the Catholic Mary, had been a cauldron of murderous prejudice both for and against Catholics, Queen Elizabeth I had been consulted during the reform process and all her senior astronomical and scientific advisers agreed with the calculations and the need to change. The newly formed Church of England however, did not, particularly because the most recent Papal Bull had excommunicated Queen Elizabeth for establishing the new Church in place of the papal, Catholic authority. The position was not helped by the attempted Spanish invasion of 1588 which had the blessing of the Catholic Church.

William Hogarth, Calendar (New Style) Act 1750

William Hogarth, 1750

Eventually, in 1750, the Calendar (New Style) Act was passed, invoking Roger Bacon’s influence on the reforms, instructing the loss of 3–13 September 1752, one day more than the original reform because the errors of the Julian calendar had pushed the date of Easter even further back.

It is difficult to imagine the strength of feeling, but there were riots in Bristol with people shouting for the return of their 11 days. There were quiet revolts too, of the bankers in the City of London: the changes meant that they would have had to pay their taxes 11 days earlier than the normal year end, which for centuries from the days of the early Saxons had been 25 March (Lady Day or the Feast of the Annunciation, the apparent date on which Jesus Christ was conceived and hence an appropriate start to the year). Prudently, they refused to lose the 11 days of interest on their money, paying on 5 April, creating the precedent which still gives us this date as the end of the financial year.

The Eastern Orthodox Church

Since the excommunications and consequential divisions of the eleventh century, co-operation between the two main limbs of Christianity – the Catholic and Eastern orthodoxy – was at best grimly courteous. At the time of Gregory’s papacy, the Eastern Orthodox Church remained at odds with the Catholic Church over its lack of support during the fall of Constantinople to the Ottomans in 1453.

1453 Siege of Constantinople

Eventually, in 1923, the Eastern orthodox faith adopted the majority of the reforms, but its calculation of leap years is based on a different system (bringing it slightly closer to the true solar year than the Gregorian) and their Easter dates retain the Julian calendar method, with the result that there can be a five-week difference in the Easter dates of the Catholic and Orthodox Christian countries.

Calendars and the Modern World

The struggle to adopt a calendar that reflects the world around us has been long and difficult, a 400 year journey of conflict between the spiritual, the political and the everyday. During that time the conflict between and within religions, and increasingly with science has intensified as technology accelerates our powers of observation and analysis.

The next post on Time will provide a quick summary of calendars before we move off to the more intimate subject of clocks!

Some other posts of interest.