The Calendar by David Ewing Duncan Fourth Estate 333pp, £12.99 in UK
As the old people in the country will still tell you, there is God's time and there is man-made time. As they see it, whether we put our clocks back or forward is irrelevant to their animals. They eat according to the hours of light and rest during darkness. And so it has been for thousands of years. Agricultural man measured time by the hours of day and night, the rise and fall of the sun. Time was a constant. Birth and death, youth and old age. Shakespeare even measured out the seven ages of an average man's life. Astronomers and mathematicians saw it differently. Time, for them, was measured by the movement of the heavenly bodies. The earliest star-gazers based their calendar on the different phases of the Moon; over 4,000 years ago, however, the Egyptians were the first to use the Sun to measure time, and it is from them that the calendar that we use is derived. Probably the most enduring result of Caesar's celebrated tryst with Cleopatra is that when he returned to Rome he brought with him Egyptian astronomers who had already worked out a year of 365 days and some odd hours, as the time it took the sun to circle the earth (as they believed). Based on this calculation, Caesar introduced the Julian Calendar which laid out the months of the year and the days of the week as we know them; indeed, Caesar's name is still commemorated in our month of July.
The Julian Calendar received the imprimatur of the early Christian Church at the Council of Nicea (325 AD) under the Emperor Constantine, and would remain the basis for calculating important feast days such as Easter and Christmas throughout the Middle Ages. In many ways it bedevilled the work of astronomers in so far as it gave a fixity to the Ptolemaic theory of the sun circling the earth, which would finally be broken by the Copernican revolution in the 16th century.
Not everyone, of course, accepted the orthodoxies of the day. The Arabs and Indians were much more advanced in mathematics and astronomy than the Europeans, and some had actually hit upon the Copernican theory of a sun-centred universe but without the telescope were unable to prove it. With their sundials and water clocks they had figured out that there was a difference between the man-made calendar and the actual time it takes the earth to rotate on its own axis and at the same time revolve around the sun. The reason for this was not known to them, as it is to us, namely that the earth wobbles and wiggles and "tilts" in an ecliptic plane as it rotates around the sun, with the result that its movements vary from year to year, providing us with the seasons.
In 1277 the English monk Roger Bacon wrote his friend Pope Clement IV that the "Kalendarium is intolerable in terms logic, horrible as astronomy and undesirable as mathematics". He had worked out calculations which would bring it back into closer proximity with the sidereal calendar, but since this could conflict with the keeping of the Easter feast, it was suppressed by his own order, and when he did get his suggestions to the Pope, he was close to death . The result was that his recommended reforms languished on the shelves for another three hundred years until 1581, when Pope Gregory XIII appointed a Commission which gave us the calendar as we now have it. The commission brought together the best mathematical and astronomical brains of the day; they resolved the anomalies by dropping ten days off the existing calendar, which went a long way towards bringing the two systems into line. Many countries, especially those under Protestant princes, were slow to accept the Gregorian Calendar. The English, under Queen Elizabeth I, respected the scholarship behind it but rejected it as coming from Rome. In fact, England waited another century before taking it on board. China only accepted it as recently as 1949. Ultimately, the deciding factor in gaining its full acceptance was the growth of trade and international transport, which required merchants to have an agreed framework in which to plan and transact their business. The Gregorian Calendar, says Duncan, is running fast against the true year by about 25.96 seconds a year. Since 1582 this has accumulated to about two hours, 59 minutes and 12 seconds and will equal an entire day about 72 generations from now - in 4909, assuming humans are still here and are using the calendar named for a Pope who died 3,330 years earlier.
These days, of course, we no longer measure time just by reference to the calendar clock. In the world of jet travel, satellite television and the technology to keep missiles on course, we use atomic time calibrated to such miniscule measures that were I to try and print it here, the figures would roll off the page. David Ewing Duncan has written a fascinating book, spelling out a highly complex subject with a minimum of jargon.
Bill Maxwell is a critic and travel writer.