A calendar’s purpose is to measure time. A day is the natural unit to use: a period of time with light, followed by another period of time with darkness.
The phases of the moon is another unit of measurement, with each quarter-phase being about seven days long; the full lunar cycle being about 29 1/2 days long.
A year is another unit of measurement. Although different definitions of a ‘year’ exist, the commonly accepted meaning of ‘year’ is the time between two successive returns of the sun to the equinox: this is what the seasons hinge upon, and is the most relevant to mankind in the day-to-day affairs. It takes just under 365 1/4 days for this cycle to transpire.
Types of calendars
Three main types of calendars exist—those based on the solar year, those based on the phases of the moon, and those that attempt to blend the phases of the moon with the solar year. The advantage of the solar calendar is that as the seasons depend on the movement of the sun, the solar calendar will coincide with the seasons; the disadvantage is that since the solar year is so long it is (was) difficult to precisely determine its length and also difficult to determine precisely where one was in the cycle without resorting to written records. The advantage of the lunar calendar is that the phases of the moon are short enough for easier reckoning of the time period; the disadvantage is that the moon phases bear no relation to the seasons. The solar-lunar calendars attempted to keep the advantages of both types of calendars.
A complication for all calendars is that the length of a day does not evenly divide into the true length of the solar year or the full cycle of the moon. Thus, there can be no single calendar that can serve year after year—over time calendars need to have days added or subtracted to keep the calendar and seasons synchronized.
Politics and the Calendar
Early Rome is believed to have used a lunar calendar. To keep the calendar in synchronization with the seasons, a full month was added from time to time as necessary. The sacred college of Rome, known as the Pontiffs, had the responsibility of keeping the calendar in synchronization. Unfortunately, the Pontiffs were not above politics, and would shorten or lengthen a year depending on whether office holders were favored or disfavored. When Julius Caesar became emperor—and thus the head of the sacred college—the calendar was badly out of synchronization with the seasons. A side-effect of this dislocation was that festivals were no longer celebrated in the proper season. To correct this problem, Caesar added three months instead of the usual one to the year 46 BC in order to bring the calendar (and the festivals) back in synchronization with the seasons.
Julian calendar
After bringing the calendar back in line with the seasons, Caesar changed the calendar from a lunar calendar to a solar calendar. His advisors recommended that the year be 365 days long, with a leap day added every 4 years to account for the approximately 1/4 day excess in the solar year. By removing the influence of the moon from the calendar and the resulting need to add months from time to time to keep the calendar in synchronization with the seasons, Caesar removed the influence of politics from the calendar and made the calendar nearly perfect.
A couple of interesting tidbits regarding the leap day: First, the leap day was added after February 24, and was considered to be a second February 24. Romans had the practice of counting days inclusively (remember this, because it comes into play a little later), and of referring to days near the end of a month as such-and-such many days before the first of the next month. February 24 worked out to be the 6th day before March 1 (Because Romans counted inclusively, they counted Feb 24, 25, 26, 27, 28, and March 1 in their total: 6 days. Nowadays we would just count 5 days—but when in Rome, do as the Romans do!) As a result, the leap day acquired the name ‘bisextile, ‘ or ‘double-sixth’ and is sometime today still referred to as such.
Second, because of the peculiar method Romans had of inclusive counting, there was a misunderstanding of how often to apply the leap day. Caesar said to apply it every 4 years, but by counting the beginning and ending year as the Romans would have counted them, leap days were accidently added every three years instead. (Confused? Take an example—say year 1 was a leap year. Then year 2 would not be; same with year 3. By the counting method you and I use, year 4 would not be a leap year either. However, the Romans said to themselves, hmmmmmm. Count year 1, 2, and 3. Now it is year 4; time for another leap year.) This mistake was discovered after 36 years. To correct the error, leap years were dropped from 9 BC to 3 AD, and from year 4 AD on, leap years under the Julian calendar have taken place every 4 years on schedule.
Gradual movement of seasons
The only problem with the Julian calendar is that the year is not exactly 365 1/4 days long. The year is 11 minutes 14 seconds shorter than this; which seems like not much, but over the centuries amounts to about 3 days every 384 years. This difference was enough to cause problems for the Catholic Church by the 16th century.
Gregorian Calendar Reform
First, some background: In 325 AD, the Council of Nicaea decided that the Easter celebration should be the same for all the Christian Church. The date was set as the “first Sunday after the first full moon which happens upon or next after the 21st of March; if the full moon happens upon a Sunday, Easter-day is the Sunday after” (Watkins, Time Counts, page 45). Although not stated explicitly, the 21st of March was the vernal equinox at this time.
By the 16th century, the vernal equinox had drifted to about March 11. This was serious business to the Catholic Church, as the Easter celebration would slowly migrate to late Spring, then Summer, and ….
Calls for the reform of the calendar had been happening for over a hundred years by the time Pope Gregory XIII took action in 1582. After consulting astronomers, scholars, and Catholics, and after obtaining their general approval, the Pope issued a statement providing that: A) To restore the vernal equinox to March 21 (as it was during the Council of Nicaea), 10 days—October 4 through the 14, 1582—were to be dropped from the calendar. B) To prevent the equinox from drifting away from March 21, years evenly divisible by 100 were not to be leap years, unless the year was also evenly divisible by 400. Thus, the Julian Calendar’s error of 3 days in every 384 years was almost perfectly corrected. The Gregorian calendar is thus accurate to about 1 day for every 4000 years.
Adoption of the Gregorian Calendar
Naturally, Catholics and Catholic countries generally adapted the Gregorian calendar right away, or within a few months. For example, most of Italy, Spain, and Portugal adapted the calendar by dropping October 4 through 14, 1582. Belgium dropped December 22 through 31, 1582. Hungary dropped October 22 through 31, 1582, and France dropped December 10 through 19, 1582. Great Britain, being a Protestant country held out for almost 170 years, making the switch by dropping September 3 through 13, 1752. Russia switched after the 1918 revolution. (Ever wonder why the “October Revolution” was celebrated in November? The end of October in the Julian calendar is the beginning of November in the Gregorian calendar…) Different adoption dates made for interesting conversions to the individuals living during these times, and for a puzzling situation to us now (How could someone reply, on the 10th of June, to a letter written on the 15th of June?!)
More Calendar Reform?
Calls for Calendar Reform continue; but they are muted calls. Since the early part of the 20th century and continuing until the late 1950s, the World Calendar Association put before the League of Nations and the United Nations proposals for a true perpetual calendar. When the United States refused to consider the proposals in the United Nations, the topic was tabled indefinitely.
The World Calendar is intended to correct the problems caused by the days of the week drifting across months, changing year to year, and the effects of holidays also moving. The problem is felt by businesses when planning payroll, by schools when planning the school year, by statisticians when trying to compare results from one quarter to the next.
Books on the World Calendar probably exist in your local public library. If you are interested, look them up under the subject ‘calendar’. The subject has not had much attention since the late 1950s but the idea is interesting nevertheless.
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Sources:
The Calendar: its history, structure and improvement by Alexander Philip, Cambridge 1921
Measures, Weights, & Moneys of All Nations by WSB Woolhouse, 7th edition, Crosby Lockwood and Son, London, 1890
The Improvement of the Gregorian calendar by Alexander Philip, EPDutton & Co, New York 1918
Time Counts: the story of the calendar by Harold Watkins, Philosophical Library Inc, New York 1954
The Book of Calendars, Frank Parise(1982) Facts On File
Other Books (that I wish I could have read, but no local library had them available):
Peter Archer: The Christian calendar and the Gregorian Reform (1941)
Issac Asimov: The Clock We Live On (1963)
JJ Bond: Handy Book of Rules and tables for verifying dates, 1869 (1st Edition), 1889 (4th edition)
William Hales: A New Analysis of Chronology, 1809
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Thank You to James Divine from West Richland, Washington who asked for more detail regarding the history of the calendar. I hope this essay meets with your approval.
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