Calendar reform

Calendar reform is any proposed reform of a calendar.

Historically, most calendar reforms have been made in order to synchronize the calendar in use with the astronomical year (either solar or sideral) and/or the synodic month in lunar or lunisolar calendars.

The Gregorian calendar is currently used by most of the world. It was the consequence of Pope Gregory XIII's reform of the Julian calendar, which was, itself, the reform under Julius Caesar of the existing Roman calendar.

Subsequent proposals have since been made to make the Gregorian calendar more useful.

Most reforms for calendars have been to make them more accurate. This has happened to various lunar and lunisolar calendars and also the Julian calendar when it was modified into the Gregorian calendar.

There have been 50 to 100 reforms of the traditional Chinese calendar over 2500 years, most of which were intended to better fit the calendar months to astronomical lunations and to more accurately add the extra month so that the regular months maintain their proper seasonal positions, even though each seasonal marker can occur anywhere within its month. There have been at least four similar reforms of the lunisolar version of the Hindu calendar, all intended to make the month a better match to the lunation and to make the year a better fit to the sidereal year. There have been reforms of the 'solar' version of the Hindu calendar which changed the distribution of the days in each month to better match the length of time that the Sun spends in each sidereal zodiacal sign. The same applies to the Buddhist calendar. The first millennium reform of the Hebrew calendar changed it from an observational calendar into a calculated calendar. The Islamic calendar was a reform of the preceding lunisolar calendar which utterly divorced it from the solar year.

At the time at which Julius Caesar took power in Rome, the Roman calendar had ceased to reflect the year accurately. The provision of adding an intercalary month to the year when needed had not been applied consistently, because it affected the length of terms of office.

The Julian reform lengthened the months (except February, owing to its religious significance) and provided for an intercalary day to be added every four years to February, creating a leap year.

This produced a noticeably more accurate calendar, but it was based on the calculation of a year as 365 days and 6 hours. In fact, the year is 11 minutes and 14 seconds less than that. This had the effect of adding three-quarters of an hour to a year, and the effect accumulated. By the sixteenth century, the vernal equinox fell on March 10.

Under Pope Gregory XIII, two reforms were effected: ten days were dropped from one year, to bring the calendar back into synchronization, and then to have century years, which are divisable by four, nevertheless not be leap years unless they are also divisible by 400. While this does not synchronize the years entirely, it would require 35 centuries to accumulate a day.

This reform slowly spread through the nations that used the Julian calendar, although the Russian church year still uses the Julian calendar. The times varied so widely that some countries had to drop more than ten: Great Britain, for instance, dropped eleven.

When noting dates occurring within the period, "Old Style" and "New Style" are used to distinguish which calendar was used by the person who recorded the date.

Reformers cite several problems with the Gregorian calendar:

• It is not perpetual. Each year starts on a different day of the week, and calendars expire every year.
• Months are not equal in length, requiring the mnemonic rhyme, "Thirty days hath September…" to remember which month is 28, 29, 30, or 31 days long.
• It is difficult to determine the weekday of any given day of the year.
• The year’s four quarters are not equal. Business quarters that are equal would make accounting easier.
• Its epoch (origin) is not religiously neutral. The same applies to month and weekday names in many languages.
• Each month has no connection with the Moon.

Many calendar reforms have offered solutions to make the calendar perpetual. These reforms would make it easy to work out the day of week of a particular date, and would make changing calendars each year unnecessary.

These make it easier to work out the day of week by having exactly 52 weeks in each year plus an extra day not belonging to any week and also having the leap day outside of any week.

For example, The World Calendar and the International Fixed Calendar are proposals that start each month on a Sunday. The remaining 364 days then form 52 weeks of 7 days. The World Calendar has every third month beginning on the same day of week.

Both of these calendars treat one or two days (the 365th day, and the 366th leap year day) each year as outside of any week or month in order to keep the calendar perpetual. In The World Calendar, these days are considered holidays and named Worlds Day and Leap Year Day. These "off-calendar", or "intercalary", days stand outside the seven-day week and caused some religious groups to strongly oppose adoption of The World Calendar. Such concerns helped prevent The World Calendar from being adopted in the 1940s and 1950s.

Supporters of The World Calendar, however, argue that the religious groups' opposition overlooked every individual's right to celebrate these holidays as extra days of worship, or Sabbaths. This option, they reason, maintains the seven-day worship cycle for those who share that concern, while allowing benefits of a perpetual calendar to be shared by all.

Some calendar reform ideas, such as the Pax Calendar, Bonavian Civil Calendar, New Earth Calendar, Symmetry454 calendar and the Common-Civil-Calendar-and-Time Calendar, were created to solve this problem by having years of either 364 days (52 weeks) or 371 days (53 weeks), thus preserving the 7-day week.

These calendars add a leap week of seven days to the calendar every five or six years to keep the calendar roughly in step with the tropical year.

The Bonvaian Civil and Symmetry454 calendars have months of 28 and 35 days, and a leap week in December, when needed. The Common-Civil-Calendar-and-Time Calendar has months of 30 and 31 days, but includes an occasional 7-day leap week named “Newton”.

The 53-week calendar, used in government and in business for fiscal years, is a variant of this concept. Each year of this calendar can be up to 371 days long.

Still other proposals, like the 30x11 Calendar, abandon attempts to make the calendar perpetual, instead opting for eleven 30-day months and one "long month" of December at 35 days, or 36 days in leap years.

Some calendar reformers seek to equalize the length of each month in the year. This is accomplished by creating a calendar that has 13 months of 28-days each, making 364 days.

An early 13-month proposal was the 1849 Positivist calendar, created by Auguste Comte. It was based on a 364-day year which included one or two "blank" days. Each of the 13 months had 28 days and exactly four weeks, and each started on a Monday. The International Fixed Calendar is a more modern descendant of this calendar.

Another example of the use of "blank" days is the 13 moon calendar, which views the uncounted 365th and 366th days as "days out of time".

Some proposals, such as the Sol Calendar, add one or two days to the calendar each year to account for the annual solar cycle, while others keep these days off the calendar entirely, to make the calendar perpetual.

Around 1930 Colligan invented the Pax Calendar, which avoids off-calendar days by adding a 7-day leap week to the perpetual 364-day year for 71 out of 400 years. The New Earth Calendar does likewise by adding a leap week once every 5 years with exceptions.

The Hermetic Lunar Week Calendar is a lunisolar calendar proposal which has 12 or 13 lunar months of 29 or 30 days a year, and begins each year near the vernal equinox.

The Simple Lunisolar Calendar uses 12 or 13 lunar months of 30 or 29 days with fixed lengths, and begins each year between Gregorian December 3 and January 1.

The Rectified Hebrew calendar uses a more accurate leap month cycle of 4366 months every 353 years, intended to replace the 19-year cycle of the modern Hebrew calendar.

The Irvember Calendar simply has the same names for the months as the Gregorian calendar but adds an extra month called Irvember after December. Each year starts 78 years before the vernal equinox or near to that. It uses the same leap rule as the Rectified Hebrew Calendar: 130 leap years per 353 year cycle.

Calendar proposals that introduce a thirteenth month or change the Julian-Gregorian system of months often also propose new names for these months. New names have also been proposed for days out of the week cycle (e.g. 365th and leap) and weeks out of the month cycle. In The World Calendar, for example, the last day of the year is "Worldsday".

Proposals to change the traditional month and weekday names are less frequent. The Gregorian calendar obtains its names mostly from gods of now obsolete religions (e.g. Thursday from Nordic Thor or March from Roman Mars) or leaders of vanished empires (July and August from the first Cæsars), or ordinals that got out of synchronization (September through December, originally seventh through tenth, now ninth through twelfth).

Calendar reformers, therefore, seek to correct what they see as deficiencies by focusing on more homogeneous sets of individuals, who usually share common traits.

Comte's Postitivst calendar, for example, proposed naming the 13 months in his calendar after figures from religion, literature, philosophy and science: Moses, Homer, Aristotle, Archimedes, Caesar, Saint Paul, Charlemagne, Dante, Gutenberg, Shakespeare, Descartes.

Similarly, the Hermetic Lunar Week Calendar uses 12 or 13 lunar months named after 13 pioneers in contributers to research for physioactive plants and chemicals: Artaud; Benjamin; Clark; De Quincy; Ellis; Furst; Grof; Hofmann; Izumi; Janiger; Kesey; Lilly; and leap month McKenna.

The Simple Lunisolar Calendar names its months after the letters of the Greek alphabet: Alpha; Beta; Gamma; Delta; Epsilon; Zeta; Eta; Theta; Iota; Kappa; Lambda; Mu; and leap month Nu.

• Calculating the day of the week

There have been many specific calendar proposals to replace the Gregorian Calendar:

The following count one or more days outside the standard seven-day week:

• Positivist Calendar
• The World Calendar
• International Fixed Calendar

The following are leap week calendars:

• Pax Calendar
• Bonavian Civil Calendar
• Common-Civil-Calendar-and-Time: C&T
• New Earth Calendar
• Symmetry454

The following simplify the months without making each year begin on the same day of the week:

• Sol Calendar
• The 30x11 Calendar

The following track the moon as well as the sun:

• Hermetic Lunar Week Calendar
• The Simple Lunisolar Calendar
• Rectified Hebrew calendar
• Irvember Calendar

There have also been proposals to revise the way years are numbered:

• Holocene calendar
• Jomon Era

• Steel, Duncan (2000). Marking Time: The Epic Quest to Invent the Perfect Calendar. New York: Wiley. ISBN 0471298271.

• Calendar Reform by Rick McCarty
• Calendar Zone Reform Calendars
• A New Calendar - options for calendar reform
• Leap week calendars in which each year has either 364 or 371 days
• C&T calendar home page
• Slashdot discussion of Dick Henry's C&T
• The PETIN-METON Calendar
• Johns Hopkins press release on C&T
• Bob McClennon's Refomed Weekly Calendar (Leap week rule has a drafting error)
• The Symmetry454 Calendar home page
• The 30x11 Calendar home page
• Tranquility Calendar (13-month calendar)
• The 13-Moon Change movement
• The 13-Month Sol Calendar
• The New Earth Calendar (13-month calendar)
• The Synaptic Calendar (13-month calendar)
• Catholic Encyclopedia "Reform of the Calendar" Historical information