Perennial calendar

Last updated

A perennial calendar is a calendar that applies to any year, keeping the same dates, weekdays and other features.

Contents

Perennial calendar systems differ from most widely used calendars which are annual calendars. Annual calendars include features particular to the year represented, and expire at the year's end. A perennial calendar differs also from a perpetual calendar, which is a tool or reference to compute the weekdays of dates for any given year, or for representing a wide range of annual calendars.

For example, most representations of the Gregorian calendar year include weekdays and are therefore annual calendars, because the weekdays of its dates vary from year to year. For this reason, proposals to perennialize the Gregorian calendar typically introduce one or another scheme for fixing its dates on the same weekdays every year.

History and background

The term perennial calendar appeared as early as 1824, in the title of Thomas Ignatius Maria Forster's Perennial calendar and companion to the almanack. [1] In that work he compiled "the events of every day in the year, as connected with history, chronology, botany, natural history, astronomy, popular customs and antiquities, with useful rules of health, observations on the weather, explanations of the feasts and festivals of the church and other miscellaneous useful information". The data listed there for each date in the calendar apply in every year, and supplement data to be found in annual almanacs. Often printed in perennial-calendar format also are book blanks for diaries, ledgers and logs, for use in any year. Entries on the blank pages of these books are organized by calendar dates, without reference to weekdays or year numbers.

Calendar reform

A goal of modern calendar reform has been to achieve universal acceptance of a perennial calendar, with dates fixed always on the same weekdays, so the same calendar table serves year after year. Advantages claimed for a perennial over an annualized calendar like the Gregorian are simplicity and regularity. Scheduling is simplified for institutions and industries with extended production cycles. School terms and breaks, for example, can fall annually on the same dates. Month-based ordinal dating ("Fourth Thursday in November", "Last Monday in May") will be obsolete. Two methods favored for perennializing the calendar are the introduction of so-called "blank days" and of a periodic "leap week".

Blank-day calendars

Blank-day calendars remove a day or two (the latter for leap years) from the weekday cycle, resulting in a year length of 364 weekdays. Since this number is evenly divisible by 7, every year can begin on the same weekday. In the twelve-month plan of The World Calendar, for example, the Gregorian year-end date of December 31 is sequestered from the cycle of the week and celebrated as "Worldsday". December 30 falls on a Saturday, Worldsday follows next, and then January 1 begins every new year on a Sunday. The extra day in leap year is treated similarly. Blank-day calendars with thirteen months have also been developed. Among them are: The Georgian calendar, by Hirossa Ap-Iccim (=Rev. Hugh Jones) (1745); [2] The Positivist calendar, by Auguste Comte (1849); and the International Fixed Calendar, by Moses B. Cotsworth (1902), [3] and championed by George Eastman. [4] Blank-day reform proposals face a religious objection, however. Sabbatarians, who are obliged to regard every seventh day as a day of rest and worship, must observe their holy day on a different weekday each year.

Leap-week calendars

Leap week calendar plans often restrict common years to 364 days, or 52 weeks, and expand leap years to 371 days, or 53 weeks. The added week may extend an existing month, or it may stand alone as an inserted seven-day month.

The leap-week calendar may have been conceived originally by Rev. George M. Searle (1839-1918), around 1905. In 1930, James A. Colligan, S.J. proposed a thirteen-month reform, the Pax Calendar. By 1955, Cecil L. Woods proposed the twelve-month Jubilee Calendar which inserts an extra week called "Jubilee" before January in specified years. [5] The Hanke–Henry Permanent Calendar (2003) inserts an extra year-end month of seven days called "Xtra", and the Symmetry454 calendar (circa 2004) lengthens the month of December by one week on leap years.

Easter in leap-week calendars

The Christian celebration of Easter is historically calculated to occur on the first Sunday after the first ecclesiastical full moon falling on or after 21 March. In leap-week calendars, March 21 is less likely to match astronomical spring equinox than in the Gregorian calendar. [6] The Symmetry454 calendar proposes Sunday, April 7 as a permanently fixed date for Easter, based on the median date of the Sunday after the day of the astronomical lunar opposition that is on or after the day of the astronomical northward equinox, calculated for the meridian of Jerusalem. [7] In 1963 the Second Ecumenical Council of the Vatican declared:

"[The Vatican] would not object if the feast of Easter were assigned to a particular Sunday of the Gregorian Calendar... [and] does not oppose efforts designed to introduce a perpetual calendar into civil society."

— Second Ecumenical Council of the Vatican, CONSTITUTION ON THE SACRED LITURGY SACROSANCTUM CONCILIUM SOLEMNLY PROMULGATED BY HIS HOLINESS POPE PAUL VI ON DECEMBER 4, 1963 [8]

Determining leap weeks

In the Pax Calendar, the extra week is added in every year having its last number, or its last two numbers, divisible by 6, and in every year ending with the number 99, and every centennial year not divisible by 400. The Hanke-Henry Permanent Calendar's leap week occurs every year that either begins or ends in a Thursday on the corresponding Gregorian calendar. The Symmetry454 calendar's leap week formula was chosen over others based on 10 criteria, including smoothest distribution of weeks, minimal "jitter" and predicted accuracy of 4-5 millennia. [9]

Objections

Objections to leap weeks include the inconvenience of a periodic extra week for billing and payment cycles, and for dividing the leap year into halves and quarters. Another objection is that anniversaries, such as birthdays, are more likely on average to occur on a leap week than a leap day.

Other options

Besides blank-day and leap-week reforms only a few other options for achieving a perennial calendar have been suggested. The Long-Sabbath Calendar, by Rick McCarty (1996), extends to 36 hours the last Saturday of the year and the subsequent first Sunday of the new year. Seventy-two hours are thereby covered with two weekdays instead of the usual three, which shortens the year to 364 calendar days without interrupting the weekday cycle. Another option would trim every year to exactly 364 days, allowing the calendar months to drift relative to the seasons. January would move from mid-winter to mid-summer, in the northern hemisphere, after approximately 150 years. The calendar year can be reckoned to drift though all the seasons once every 294 calendar years equal to 293 years of 365.2423208191 days.

See also

Related Research Articles

Intercalation or embolism in timekeeping is the insertion of a leap day, week, or month into some calendar years to make the calendar follow the seasons or moon phases. Lunisolar calendars may require intercalations of both days and months.

The International Fixed Calendar is a proposed calendar reform designed by Moses B. Cotsworth, first presented in 1902. The solar calendar divides the year into 13 months of 28 days each. A type of perennial calendar, every date is fixed to the same weekday every year. Though it was never officially adopted at the country level, the entrepreneur George Eastman instituted its use at the Eastman Kodak Company in 1928, where it was used until 1989. While it is sometimes described as the 13-month calendar or the equal-month calendar, various alternative calendar designs share these features.

Reform of the date of Easter refers to proposals to change the date for the annual celebration of Easter. These proposals include setting a fixed date or agreeing between Eastern and Western Christendom a common basis for calculating the date of Easter so that all Christians celebrate the Festival on the same day. As of 2023, no such agreement has been reached.

The World Calendar is a proposed reform of the Gregorian calendar created by Elisabeth Achelis of Brooklyn, New York in 1930.

<span class="mw-page-title-main">Date of Easter</span> Calculation of its date

As a moveable feast, the date of Easter is determined in each year through a calculation known as computus. Easter is celebrated on the first Sunday after the Paschal full moon, which is the first full moon on or after 21 March. Determining this date in advance requires a correlation between the lunar months and the solar year, while also accounting for the month, date, and weekday of the Julian or Gregorian calendar. The complexity of the algorithm arises because of the desire to associate the date of Easter with the date of the Jewish feast of Passover which, Christians believe, is when Jesus was crucified.

Calendar reform or calendrical reform is any significant revision of a calendar system. The term sometimes is used instead for a proposal to switch to a different calendar design.

A leap year starting on Saturday is any year with 366 days that begins on Saturday, 1 January, and ends on Sunday, 31 December. Its dominical letters hence are BA. The most recent year of such kind was 2000 and the next one will be 2028 in the Gregorian calendar or, likewise 2012 and 2040 in the obsolescent Julian calendar. In the Gregorian calendar, years divisible by 400 are always leap years starting on Saturday. The most recent such occurrence was 2000 and the next one will be 2400, see below for more.

The positivist calendar was a calendar reform proposal by Auguste Comte (1798–1857) in 1849. Revising the earlier work of Marco Mastrofini, or an even earlier proposal by "Hirossa Ap-Iccim", Comte developed a solar calendar with 13 months of 28 days, and an additional festival day commemorating the dead, totalling 365 days.

The determination of the day of the week for any date may be performed with a variety of algorithms. In addition, perpetual calendars require no calculation by the user, and are essentially lookup tables. A typical application is to calculate the day of the week on which someone was born or a specific event occurred.

A leap week calendar is a calendar system with a whole number of weeks in a year, and with every year starting on the same weekday. Most leap week calendars are proposed reforms to the civil calendar, in order to achieve a perennial calendar. Some, however, such as the ISO week date calendar, are simply conveniences for specific purposes.

<span class="mw-page-title-main">Perpetual calendar</span> Calendar designed to look up the day of the week for a given date

A perpetual calendar is a calendar valid for many years, usually designed to look up the day of the week for a given date in the past or future.

<span class="mw-page-title-main">George Mary Searle</span> American astronomer (1839–1918)

George Mary Searle was an American astronomer and Catholic priest.

<span class="mw-page-title-main">Doomsday rule</span> Way of calculating the day of the week of a given date

The Doomsday rule, Doomsday algorithm or Doomsday method is an algorithm of determination of the day of the week for a given date. It provides a perpetual calendar because the Gregorian calendar moves in cycles of 400 years. The algorithm for mental calculation was devised by John Conway in 1973, drawing inspiration from Lewis Carroll's perpetual calendar algorithm. It takes advantage of each year having a certain day of the week upon which certain easy-to-remember dates, called the doomsdays, fall; for example, the last day of February, 4/4, 6/6, 8/8, 10/10, and 12/12 all occur on the same day of the week in any year.

The Symmetry454 calendar (Sym454) is a proposal for calendar reform created by Irv Bromberg of the University of Toronto, Canada. It is a perennial solar calendar that conserves the traditional month pattern and 7-day week, has symmetrical equal quarters in 82% of the years in its 293-year cycle, and starts every month on Monday.

The Pax calendar was invented by James A. Colligan, SJ in 1930, as a perennializing reform of the annualized Gregorian calendar.

The ISO week date system is effectively a leap week calendar system that is part of the ISO 8601 date and time standard issued by the International Organization for Standardization (ISO) since 1988 and, before that, it was defined in ISO (R) 2015 since 1971. It is used (mainly) in government and business for fiscal years, as well as in timekeeping. This was previously known as "Industrial date coding". The system specifies a week year atop the Gregorian calendar by defining a notation for ordinal weeks of the year.

An annual calendar is a representation of the year that expires with the year represented, or that must be altered annually to remain current. The term takes different but related meanings across two contexts. One is for static (synchronic) calendars, such as wall calendars or calendar systems. The other is for dynamic (diachronic) calendars, such as digital calendars or timepieces. Static representations of the Gregorian calendar year are annual, because the weekdays of Gregorian dates vary from year to year. The calendar representing one year will not serve for the next year. With perennial calendars, the same representation of the year serves for every year. Perpetual calendars, in this context, are computation devices for determining the weekdays of dates in any given year, or for representing a wide range of annual calendars.

The Gregorian calendar is the calendar used in most parts of the world. It went into effect in October 1582 following the papal bull Inter gravissimas issued by Pope Gregory XIII, which introduced it as a modification of, and replacement for, the Julian calendar. The principal change was to space leap years differently so as to make the average calendar year 365.2425 days long, more closely approximating the 365.2422-day 'tropical' or 'solar' year that is determined by the Earth's revolution around the Sun.

Armelin's calendar was developed around 1887 by French astronomer Gaston Armelin, who developed a twelve-month calendar in which the year of 364 days was divided into four equal quarters of 91 days.

The Hanke–Henry Permanent Calendar (HHPC) is a proposal for calendar reform. It is one of many examples of leap week calendars, calendars that maintain synchronization with the solar year by intercalating entire weeks rather than single days. It is a modification of a previous proposal, Common-Civil-Calendar-and-Time (CCC&T). With the Hanke–Henry Permanent Calendar, every calendar date always falls on the same day of the week. A major feature of the calendar system is the abolition of time zones.

References

  1. ↑ Thomas Ignatius M. Forster, Perennial calendar and companion to the almanack (London: Harding, Mavor and Lepard, 1824)
  2. ↑ Hirossa Ap-Iccim, "An Essay on the British Computation of Time, Coins, Weights, and Measures, and a Proposal for a New Georgian Æra, not to Err a Day in 10,000 Years", The Gentleman’s Magazine, 15 (1745): 377-379
  3. ↑ Moses B. Cotsworth, The rational almanac: tracing the evolution of modern almanacs from ancient ideas of time, and suggesting improvements (Acomb, England:Cotsworth, 1905)
  4. ↑ Frank Parker Stockbridge, "New Calendar by 1933 -- Eastman", Popular Science Monthly (June 1929): 32
  5. ↑ Elisabeth Achelis, "OCCASIONAL LEAP-WEEKS NOT PRACTICAL", The Journal of Calendar Reform, 25 (Dec. 1955-Jan. 1956): 187-190
  6. ↑ Edward L. Cohen, "Adoption and Reform of the Gregorian Calendar", in Deanna Haunsperger, Stephen Kennedy, eds., The edge of the universe: celebrating 10 years of Math horizons (Washington, D.C.: Mathematical Association of America, 2006), pp. 129-134
  7. ↑ Bromberg, Irv. "The Symmetry010 Calendar". Symmetry454 and Symmetry010 Calendars, Kalendis Calculator, and more. Retrieved 6 August 2016.
  8. ↑ Montini, Giovanni. "CONSTITUTION ON THE SACRED LITURGY SACROSANCTUM CONCILIUM SOLEMNLY PROMULGATED BY HIS HOLINESS POPE PAUL VI ON DECEMBER 4, 1963". Sacrosanctum concilium - La Santa Sede. Second Ecumenical Council of the Vatican. Retrieved 6 August 2016.
  9. ↑ Bromberg, Irv. "Solar Calendar Leap Rules". Symmetry454 and Symmetry010 Calendars, Kalendis Calculator, and more. Retrieved 7 August 2016.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.