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.
Principles
The prime objective of a calendar is to unambiguously identify any day in past, present and future by a specific date in order to record or organize social, religious, commercial or administrative events. Recurring periods that contain multiple days, like weeks, months and even years, are secondary, convenient features of a calendar. Most cultures adopt a primary dating system, but different cultures have always needed to align multiple calendars with each other, because they coexisted in the same space (e.g. secular and religious groups with different demands) or had established trading relations.
Once specified, a ''calendar design'' cannot be altered without becoming a new design. If a proposed design is sufficiently close to the legacy one, i.e. compatible with it, a ''reform'' of the local ''calendar system'' is possible without disruption. Examples of this include the changes to the Chinese calendar due to problems between regions in China and practical changes in religious calendars such as the Islamic calendar where the start of the month is now derived from astronomical data rather than sightings by religious leaders.
Some design changes, however, will yield date identifiers different from the previous design for some days, often in the distant past or future.
The calendar system must clarify whether dates are changed to the new design retroactively (using a ''proleptic calendar'') or whether the design in use then and there shall be respected. Calendar schisms happen if not all cultures that adopted a common calendar system before perform a calendar reform at the same time. If date identifiers are similar but different, confusion and mistakes are unavoidable.
Most calendars have several rules which could be altered by reform:
* Whether and how days are grouped into subdivisions such as
months and
week
A week is a unit of time equal to seven days. It is the standard time period used for short cycles of days in most parts of the world. The days are often used to indicate common work days and rest days, as well as days of worship. Weeks are of ...
s, and days outside those subdivisions, if any.
* Which years are
leap year
A leap year (also known as an intercalary year or bissextile year) is a calendar year that contains an additional day (or, in the case of a lunisolar calendar, a month) added to keep the calendar year synchronized with the astronomical year or ...
s and
common years and how they differ.
* Numbering of years, selection of the
epoch
In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured.
The moment of epoch is usually decided by ...
, and the issue of
year zero
A year zero does not exist in the Anno Domini (AD) calendar year system commonly used to number years in the Gregorian calendar (nor in its predecessor, the Julian calendar); in this system, the year is followed directly by year . However, the ...
.
* Start of the year (such as the
December solstice, January 1, March 1,
March equinox
The March equinox or northward equinox is the equinox on the Earth when the subsolar point appears to leave the Southern Hemisphere and cross the celestial equator, heading northward as seen from Earth. The March equinox is known as the ve ...
,
Lady Day
In the Western liturgical year, Lady Day is the traditional name in some English-speaking countries of the Feast of the Annunciation, which is celebrated on 25 March, and commemorates the visit of the archangel Gabriel to the Virgin Mary, durin ...
).
* If a week is retained, the start, length, and names of its days.
* Start of the day (midnight, sunrise, noon, or sunset).
* If months are retained, number, lengths, and names of months.
* Special days and periods (such as leap day or intercalary day).
* Alignment with social cycles.
* Alignment with astronomical cycles.
* Alignment with biological cycles.
* Literal notation of dates.
Historical reforms
Historically, most calendar reforms have been made in order to synchronize the calendar with the astronomical year (either
solar or
sidereal) and/or the
synodic month
In lunar calendars, a lunar month is the time between two successive syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month.
Variations
In Shona, Middle Eastern, and Euro ...
in
lunar
Lunar most commonly means "of or relating to the Moon".
Lunar may also refer to:
Arts and entertainment
* ''Lunar'' (series), a series of video games
* "Lunar" (song), by David Guetta
* "Lunar", a song by Priestess from the 2009 album ''Prior t ...
or
lunisolar calendar
A lunisolar calendar is a calendar in many cultures, combining lunar calendars and solar calendars. The date of Lunisolar calendars therefore indicates both the Moon phase and the time of the solar year, that is the position of the Sun in the ...
s. 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 altered to the Gregorian calendar.
The fundamental problems of the calendar are that the astronomical year has neither a whole number of days nor a whole number of lunar months; neither does the lunar month have a whole number of days: in each case there are fractions "left over". (In some physical circumstances the rotations and revolutions of a planet and its satellite(s) can be phase-locked —for example the same side of the moon always faces us— but this has not operated to lock together the lengths of the Earth's year, day and month.) Such remainders could accumulate from one period to the next, thereby driving the cycles out of synchronization.
A typical solution to force synchronization is
intercalation. This means occasionally adding an extra day (or month) into the cycle. An alternative approach is to ignore the mismatch and simply let the cycles continue to drift apart. The general approaches include:
* The lunar calendar, which fits days into the cycle of lunar months, adding an extra day when needed, while ignoring the annual solar cycle of the seasons.
* The solar calendar, which fits artificial months into the year, adding an extra day into one month when needed, while ignoring the lunar cycle of new/full moons.
* The lunisolar calendar, which keeps both the lunar and solar cycles, adding an extra month into the year when needed.
An obvious disadvantage of the lunisolar method of inserting a whole extra month is the large irregularity of the length of the year from one to the next. The simplicity of a lunar calendar has always been outweighed by its inability to track the seasons, and a solar calendar is used in conjunction to remedy this defect. Identifying the lunar cycle month requires straightforward observation of the Moon on a clear night. However, identifying seasonal cycles requires much more methodical observation of stars or a device to track solar day-to-day progression, such as that established at places like
Stonehenge. After centuries of empirical observations, the theoretical aspects of calendar construction could become more refined, enabling predictions that identified the need for reform.
Reform of lunar and lunisolar calendars
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
The Hindu calendar, Panchanga () or Panjika is one of various lunisolar calendars that are traditionally used in the Indian subcontinent and Southeast Asia, with further regional variations for social and Hindu religious purposes. They adopt a ...
, 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 Buddhist calendar is a set of lunisolar calendars primarily used in Cambodia, Laos, Myanmar, India, Sri Lanka, and Thailand as well as in Malaysia, Singapore and Vietnam by Chinese populations for religious or official occasions. While t ...
. The first millennium reform of the
Hebrew calendar
The Hebrew calendar ( he, הַלּוּחַ הָעִבְרִי, translit=HaLuah HaIvri), also called the Jewish calendar, is a lunisolar calendar used today for Jewish religious observance, and as an official calendar of the state of Israel. ...
changed it from an observational calendar into a calculated calendar. The
Islamic calendar
The Hijri calendar ( ar, ٱلتَّقْوِيم ٱلْهِجْرِيّ, translit=al-taqwīm al-hijrī), also known in English as the Muslim calendar and Islamic calendar, is a lunar calendar consisting of 12 lunar months in a year of 354 ...
was a reform of the preceding lunisolar calendar which completely divorced it from the solar year.
Another reform was performed in
Seljuk Persia by
Omar Khayyam
Ghiyāth al-Dīn Abū al-Fatḥ ʿUmar ibn Ibrāhīm Nīsābūrī (18 May 1048 – 4 December 1131), commonly known as Omar Khayyam ( fa, عمر خیّام), was a polymath, known for his contributions to mathematics, astronomy, philosophy, an ...
and others, developing the precisely computed
Jalali calendar
The Jalali calendar is a solar calendar, was compiled during the reign of Jalaluddin Malik-Shah I of Seljuk by the order of Nizam al-Mulk and the place of observation were the cities of Isfahan (the capital of the Seljuks), Rey, and Nishapur ...
.
Julian and Gregorian reforms
When
Julius Caesar
Gaius Julius Caesar (; ; 12 July 100 BC – 15 March 44 BC), was a Roman general and statesman. A member of the First Triumvirate, Caesar led the Roman armies in the Gallic Wars before defeating his political rival Pompey in a civil war, ...
took power in Rome, the
Roman calendar
The Roman calendar was the calendar used by the Roman Kingdom and Roman Republic. The term often includes the Julian calendar established by the reforms of the dictator Julius Caesar and emperor Augustus in the late 1stcenturyBC and sometim ...
had ceased to reflect the year accurately.
The
Julian reform made 46 BC 445 days long and replaced the intercalary month with an intercalary day to be inserted within February every four years. This produced a noticeably more accurate calendar, but it had an average year length of 365 days and 6 hours (365.25 d). This had the effect of adding about three-quarters of an hour every four years. The effect accumulated from inception in 45 BC until by the 16th century the northward equinox was falling on March 10 or 11.
Under
Pope Gregory XIII
Pope Gregory XIII ( la, Gregorius XIII; it, Gregorio XIII; 7 January 1502 – 10 April 1585), born Ugo Boncompagni, was head of the Catholic Church and ruler of the Papal States from 13 May 1572 to his death in April 1585. He is best known for ...
, the
leap year rule was altered: century years would not be leap years if not evenly divisible by 400. The years 1600, 2000, 2400 and 2800 are leap years, while 1700, 1800, 1900, 2100, 2200, 2300, 2500, 2600, 2700, 2900 and 3000 would be common years despite being divisible by 4. This rule makes the mean year 365.2425 days long. While this does not synchronize the years entirely, it would require a few thousand years to accumulate a day.
So that the northward equinox would have the same date in the new Gregorian calendar as it had when the Council of Nicaea made recommendations in AD 325 (), ten days were dropped so that became in 1582.
![Julian to Gregorian Date Change](https://upload.wikimedia.org/wikipedia/commons/6/69/Julian_to_Gregorian_Date_Change.png)
This reform took a few centuries to spread through the nations that used the Julian calendar, although the Russian church year still uses the Julian calendar. Those nations that adopted this calendar on or after 1700 had to drop more than ten days: Great Britain, for instance, dropped 11.
In 1923,
Milutin Milanković
Milutin Milanković (sometimes anglicised as Milankovitch; sr-Cyrl, Милутин Миланковић ; 28 May 1879 – 12 December 1958) was a Serbian mathematician, astronomer, climatologist, geophysicist, civil engineer and popularizer of ...
proposed to a
synod of some
Eastern Orthodox Church
The Eastern Orthodox Church, also called the Orthodox Church, is the second-largest Christian church, with approximately 220 million baptized members. It operates as a communion of autocephalous churches, each governed by its bishops vi ...
es at
Constantinople
la, Constantinopolis ota, قسطنطينيه
, alternate_name = Byzantion (earlier Greek name), Nova Roma ("New Rome"), Miklagard/Miklagarth (Old Norse), Tsargrad ( Slavic), Qustantiniya ( Arabic), Basileuousa ("Queen of Cities"), Megalopolis ( ...
that only those centennial years (those ending in 00) that leave a remainder of 200 or 600 upon division by 900 would be leap years, decreasing the average year length to 365.24 days. These remainders were chosen to delay as much as possible the first year (after 1923) that this calendar would disagree with the Gregorian calendar, until 2800. It was adopted by some Eastern Orthodox Churches under the names
Revised Julian calendar
The Revised Julian calendar, or less formally the new calendar, is a calendar proposed in 1923 by the Serbian scientist Milutin Milanković as a more accurate alternative to both Julian and Gregorian calendars. At the time, the Julian calendar ...
or New calendar, but was rejected by others.
Proposals
The
Gregorian calendar
The Gregorian calendar is the calendar used in most parts of the world. It was introduced in October 1582 by Pope Gregory XIII as a modification of, and replacement for, the Julian calendar. The principal change was to space leap years dif ...
is currently used by most of the world. There is also an international standard describing the calendar,
ISO 8601
ISO 8601 is an international standard covering the worldwide exchange and communication of date and time-related data. It is maintained by the Geneva-based International Organization for Standardization (ISO) and was first published in 1988, w ...
, with some differences from traditional conceptions in many cultures.
Since the papal reform in 1582, several proposals have been offered to make the Gregorian calendar more useful or regular. Very few reforms have gained official acceptance. The rather different
decimal French Republican Calendar was one such official reform, but was abolished twelve years later by
Napoleon
Napoleon Bonaparte ; it, Napoleone Bonaparte, ; co, Napulione Buonaparte. (born Napoleone Buonaparte; 15 August 1769 – 5 May 1821), later known by his regnal name Napoleon I, was a French military commander and political leader who ...
. After
World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...
, the newly formed United Nations continued efforts of its predecessor, the
League of Nations
The League of Nations (french: link=no, Société des Nations ) was the first worldwide intergovernmental organisation whose principal mission was to maintain world peace. It was founded on 10 January 1920 by the Paris Peace Conference that ...
, to establish the proposed
World Calendar
The World Calendar is a proposed reform of the Gregorian calendar created by Elisabeth Achelis of Brooklyn, New York in 1930.
Features
The World Calendar is a 12-month, perennial calendar with equal quarters.
Each quarter begins on a Sunday ...
but postponed the issue after a veto from the
government of the United States
The federal government of the United States (U.S. federal government or U.S. government) is the national government of the United States, a federal republic located primarily in North America, composed of 50 states, a city within a feder ...
, which was mainly based upon concerns of religious groups about the proposed days that would be outside the seven-day week cycle ("blank days") and thus disrupt having a sabbath every seven days. Independently the
World Council of Churches
The World Council of Churches (WCC) is a worldwide Christian inter-church organization founded in 1948 to work for the cause of ecumenism. Its full members today include the Assyrian Church of the East, the Oriental Orthodox Churches, most ju ...
still tries to find a common rule for the date of Easter, which might be eased by a new common calendar.
Reformers cite several problems with the Gregorian calendar:
* It is not
perennial
A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also wid ...
. Each year starts on a different day of the week and calendars expire every year.
* It is difficult to determine the weekday of any given day of the year or month.
* Months are not equal in length, nor regularly distributed across the year, and so some people rely on
mnemonic
A mnemonic ( ) device, or memory device, is any learning technique that aids information retention or retrieval (remembering) in the human memory for better understanding.
Mnemonics make use of elaborative encoding, retrieval cues, and imag ...
s (e.g., "
Thirty days hath September" or
knuckle counting) to remember the lengths of months.
* The year's four quarters (of three full months each) are not equal (being of 90/91, 91, 92 and 92 days respectively).
Business quarters that are equal would make accounting easier.
* Its epoch, i.e. start of the year count, is religious. The same applies to month and
weekday
The weekdays and weekend are the complementary parts of the week devoted to labour and rest, respectively. The legal weekdays (British English), or workweek (American English), is the part of the seven-day week devoted to working. In most of t ...
names in many languages.
* Each month has no connection with the
lunar phases.
* Solstices and equinoxes do not coincide with either the beginning of the Gregorian months or the midpoint of the months.
* The calendar does not have a
year zero
A year zero does not exist in the Anno Domini (AD) calendar year system commonly used to number years in the Gregorian calendar (nor in its predecessor, the Julian calendar); in this system, the year is followed directly by year . However, the ...
: the year after
1 BC was
1 AD
__NOTOC__
AD 1 or 1 CE is the epoch year for the Anno Domini (AD) Christian calendar era and also the 1st year of the Common Era (CE) and the 1st millennium and of the 1st century of the Christian and the common era. It was a common year sta ...
, with nothing in between them.
It is hard or even impossible to solve all these issues in just one calendar.
Most plans evolve around the solar year of a little more than 365 days. This number does not divide well by seven or twelve, which are the traditional numbers of days per week and months per year respectively. The nearby numbers 360, 364 and 366 are divisible in better ways. There are also lunar-centric proposals.
Perennial calendars
Many calendar reforms have offered solutions to make the Gregorian calendar perennial. These reforms would make it easy to work out the day of the week of a particular
date
Date or dates may refer to:
*Date (fruit), the fruit of the date palm (''Phoenix dactylifera'')
Social activity
*Dating, a form of courtship involving social activity, with the aim of assessing a potential partner
** Group dating
*Play date, a ...
, and would make changing calendars each year unnecessary. There are, roughly speaking, two options to achieve this goal:
leap week calendar
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. So ...
s and
intercalary days
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.
...
. Leap week 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. They have years of either 364 days (52 weeks) or 371 days (53 weeks), thus preserving the 7-day week.
Proposals mainly differ in their selection of a leap rule, placing of the leap item (usually middle or end of the year), in the start day of the week and year, in the number (12 or 13) and size of months and in connected naming; some are compatible to the
week date of ISO 8601.
The
World Calendar
The World Calendar is a proposed reform of the Gregorian calendar created by Elisabeth Achelis of Brooklyn, New York in 1930.
Features
The World Calendar is a 12-month, perennial calendar with equal quarters.
Each quarter begins on a Sunday ...
, favored by the UN in the 1950s, and the
International Fixed Calendar
The International Fixed Calendar (also known as the IFC, Cotsworth plan, the Cotsworth calendar and the Eastman plan) is a proposed calendar reform designed by Moses B. Cotsworth, first presented in 1902. The solar calendar divides the year into ...
, quite popular among economists between the World Wars, are proposals that start each year on a Sunday. The 364 days within the week system form 52 weeks of 7 days. The World Calendar has every quarter beginning on the same day of the week. In the World Calendar, the 365th and 366th day are considered holidays and named Worlds Day and Leap Year Day. These "off-calendar" 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. 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, maintained the seven-day worship cycle for those who share that concern, while allowing benefits of a perennial calendar to be shared by all.
Some calendar reform ideas, such as the
Pax Calendar
The Pax calendar was invented by James A. Colligan, SJ in 1930 as a perennializing reform of the annualized Gregorian calendar.
Design
The common year is divided into 13 months of 28 days each, whose names are the same as in the Gregorian cal ...
,
Symmetry454
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 ...
calendar and the
Hanke-Henry Permanent 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. The 53-week calendar, used in government and in business for
fiscal year
A fiscal year (or financial year, or sometimes budget year) is used in government accounting, which varies between countries, and for budget purposes. It is also used for financial reporting by businesses and other organizations. Laws in many ...
s, is a variant of this concept. Each year of this calendar can be up to 371 days long.
Some calendars have quarters of regularly patterned uneven months e.g., a 35-day (five-week) month and a pair of 28-day (four-week) months, with a leap week appended to the final month when needed. The Common Civil Calendar and Time calendar has months of 30 and 31 days, but inserts a leap week in the middle of the year, when needed, whereas its successor, the Hanke-Henry Permanent Calendar, moves the extra week to the end of the year.
In the
World Season Calendar
yi, יצחק אזימאװ
, birth_date =
, birth_place = Petrovichi, Russian SFSR
, spouse =
, relatives =
, children = 2
, death_date =
, death_place = Manhattan, New York City, U.S.
, nationality = Russian (1920–1922)Soviet (192 ...
, months are discarded altogether; instead, the year is divided into four seasons of 13 weeks each. An extra day (two days during leap year) is added to the calendar that is not assigned a day of the week in order to perennialize the calendar. The same calendar of 91 days is used for each season of every year.
10-month calendars
A decimal calendar is a calendar which includes
units of time
A unit of time is any particular time interval, used as a standard way of measuring or expressing duration. The base unit of time in the International System of Units (SI) and by extension most of the Western world, is the second, defined as ab ...
based on the
decimal system.
The
French Republican Calendar was introduced (along with
decimal time
Decimal time is the representation of the time of day using units which are decimally related. This term is often used specifically to refer to the time system used in France for a few years beginning in 1792 during the French Revolution, whi ...
) in 1793.
It consisted of twelve months, each divided into three ''décades'' of ten days, with five or six intercalary days called ''
sansculottides
The Sansculottides (; also Epagomènes; french: Sans-culottides, Sanculottides, jours complémentaires, jours épagomènes) are holidays following the last month of the year on the French Republican calendar which was used following the French Re ...
''.
[ The calendar was abolished by ]Napoleon
Napoleon Bonaparte ; it, Napoleone Bonaparte, ; co, Napulione Buonaparte. (born Napoleone Buonaparte; 15 August 1769 – 5 May 1821), later known by his regnal name Napoleon I, was a French military commander and political leader who ...
on January 1, 1806.[
]
12-month calendars
The lengths of the months inherited from the old Roman calendar
The Roman calendar was the calendar used by the Roman Kingdom and Roman Republic. The term often includes the Julian calendar established by the reforms of the dictator Julius Caesar and emperor Augustus in the late 1stcenturyBC and sometim ...
as reformed by Julius Caesar do not follow any apparent logic systematically. Many reform proposals seek to make the pattern more uniform.
When keeping the traditional dozen months and the close approximation of a solar year, this usually yields four equal quarters of three months each where one month is longer than the other two. World Calendar
The World Calendar is a proposed reform of the Gregorian calendar created by Elisabeth Achelis of Brooklyn, New York in 1930.
Features
The World Calendar is a 12-month, perennial calendar with equal quarters.
Each quarter begins on a Sunday ...
and Hanke–Henry Permanent Calendar
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. I ...
follow this with 31:30:30 and 30:30:31 days per month, respectively. On the other hand, Symmetry454
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 ...
uses 4:5:4 weeks per month. They all result in 364 systematically distributed days and hence have to add either one extra and one leap day or a leap week.
13-month calendars
Some calendar reformers seek to equalize the length of each month in the year. This is often accomplished by creating a calendar that has 13 months of 4 weeks (28 days) each, making 364 days. The earliest known proposal of this type was the Georgian Calendar (1745) by Rev. Hugh Jones.
The Positivist calendar 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" ( Hugh Jones), Comte developed a solar calendar with 1 ...
(1849), created by Auguste Comte, 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
The International Fixed Calendar (also known as the IFC, Cotsworth plan, the Cotsworth calendar and the Eastman plan) is a proposed calendar reform designed by Moses B. Cotsworth, first presented in 1902. The solar calendar divides the year into ...
is a more modern descendant of this calendar.
Around 1930, one James Colligan invented the Pax Calendar
The Pax calendar was invented by James A. Colligan, SJ in 1930 as a perennializing reform of the annualized Gregorian calendar.
Design
The common year is divided into 13 months of 28 days each, whose names are the same as in the Gregorian cal ...
, which avoids off-calendar days by adding a 7-day leap week
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. S ...
to the 364-day common year for 71 out of 400 years.
Lunisolar calendars
Lunisolar calendars usually have 12 or 13 months of 29 or 30 days.
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 Meyer-Palmen Solilunar Calendar has 12 lunar months with 29 or 30 days plus a leap month called Meton
Meton of Athens ( el, Μέτων ὁ Ἀθηναῖος; ''gen''.: Μέτωνος) was a Ancient Greece, Greek mathematician, astronomer, list of geometers, geometer, and engineer who lived in Athens in the 5th century BC. He is best known for ...
every 3 or 2 years with 30 or 31 days. 60 years together are called a cycle. It uses a leap cycle which has equal number of days, weeks, months, years and cycles. 2498258 days, 356894 weeks, 84599 months, 6840 years and 114 cycles nearly all equal each other. It is called an era, although time isn't divided into it in this calendar.
Some propose to improve leap rules of existing calendars, such as the Hebrew calendar
The Hebrew calendar ( he, הַלּוּחַ הָעִבְרִי, translit=HaLuah HaIvri), also called the Jewish calendar, is a lunisolar calendar used today for Jewish religious observance, and as an official calendar of the state of Israel. ...
. The Rectified Hebrew calendar uses a more accurate leap cycle of 4366 months per 353-year cycle, with 130 leap years per cycle, and a progressively shorter ''molad
''Molad'' (מולד, plural ''Moladot'', מולדות) is a Hebrew word meaning "birth" that also generically refers to the time at which the New Moon is "born". The word is ambiguous, however, because depending on the context, it could refer to th ...
'' interval, intended to replace the 19-year leap cycle and the constant ''molad'' interval of the traditional fixed arithmetic Hebrew calendar, respectively.
Naming
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.
Proposals to change the traditional month and weekday names are less frequent. The Gregorian calendar obtains its names mostly from gods of historical religions (e.g., Thursday from Nordic Thor
Thor (; from non, Þórr ) is a prominent god in Germanic paganism. In Norse mythology, he is a hammer-wielding god associated with lightning, thunder, storms, sacred groves and trees, strength, the protection of humankind, hallowing, an ...
or March from Roman Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
) or leaders of vanished empires (July and August from the first Caesars), or ordinals that got out of synchronization (September through December, originally seventh through tenth, now ninth through twelfth).
Examples
Comte's Positivist calendar, for example, proposed naming the 13 months in his calendar after figures from religion, literature, philosophy and science. Similarly, the Hermetic Lunar Week Calendar uses 12 or 13 lunar months named after 13 contributors to research on psychoactive plant
Psychoactive plants are plants, or preparations thereof, that upon ingestion induce psychotropic effects. As stated in a reference work:
Psychoactivity may include sedative, stimulant, euphoric, deliriant, and hallucinogenic effects.
Sever ...
s and chemicals.
Specific proposals
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:
* International Fixed Calendar
The International Fixed Calendar (also known as the IFC, Cotsworth plan, the Cotsworth calendar and the Eastman plan) is a proposed calendar reform designed by Moses B. Cotsworth, first presented in 1902. The solar calendar divides the year into ...
* Invariable Calendar
* Positivist calendar 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" ( Hugh Jones), Comte developed a solar calendar with 1 ...
* World Calendar
The World Calendar is a proposed reform of the Gregorian calendar created by Elisabeth Achelis of Brooklyn, New York in 1930.
Features
The World Calendar is a 12-month, perennial calendar with equal quarters.
Each quarter begins on a Sunday ...
* World Season Calendar
yi, יצחק אזימאװ
, birth_date =
, birth_place = Petrovichi, Russian SFSR
, spouse =
, relatives =
, children = 2
, death_date =
, death_place = Manhattan, New York City, U.S.
, nationality = Russian (1920–1922)Soviet (192 ...
The following are leap week calendars:
* Hanke-Henry Permanent Calendar
* Pax Calendar
The Pax calendar was invented by James A. Colligan, SJ in 1930 as a perennializing reform of the annualized Gregorian calendar.
Design
The common year is divided into 13 months of 28 days each, whose names are the same as in the Gregorian cal ...
* Symmetry454
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 ...
There have also been proposals to revise the way years are numbered:
* Anno Lucis
Anno Lucis (“in the Year of Light”) is a dating system used in Masonic ceremonial or commemorative proceedings, which is equivalent to the Gregorian year plus 4000. It is similar to ''Anno Mundi''.
Description
For example, a date Anno Domini ...
* Holocene calendar
The Holocene calendar, also known as the Holocene Era or Human Era (HE), is a year numbering system that adds exactly 10,000 years to the currently dominant ( AD/ BC or CE/BCE) numbering scheme, placing its first year near the beginning of the ...
Reform of the Islamic calendar:
* Since the beginning of the 21st century, there is a trend within the Muslim communities of North America and Europe to substitute a lunar calendar based on calculations for the traditional Islamic method of monthly observation of the new moon to declare the beginning of the new month in each country separately.Khalid Chraibi, The Reform of the Islamic Calendar: The Terms of the Debate, Tabsir.net, September 2012
See also
* Abolition of time zones
The abolition of time zones involves replacing time zones with Coordinated Universal Time (UTC) as a local time.
History
For most of part of history, the position of the sun was used for timekeeping. During the 19th century, most towns kept t ...
* Determination of the day of the week
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 ...
* Decimal calendar
* Hanke–Henry Permanent Calendar
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. I ...
* List of calendars
This is a list of calendars. Included are historical calendars as well as proposed ones. Historical calendars are often grouped into larger categories by cultural sphere or historical period; thus O'Neil (1976) distinguishes the groupings Egypti ...
* Metric time
Metric time is the measure of time intervals using the metric system. The modern SI system defines the second as the base unit of time, and forms multiples and submultiples with metric prefixes such as kiloseconds and milliseconds. Other unit ...
;Precursors of the Gregorian reform
* Johannes de Sacrobosco
Johannes de Sacrobosco, also written Ioannes de Sacro Bosco, later called John of Holywood or John of Holybush ( 1195 – 1256), was a scholar, monk, and astronomer who taught at the University of Paris.
He wrote a short introduction to the Hi ...
, ''De Anni Ratione'' ("On reckoning the years"), c. 1235
* Roger Bacon, ''Opus Majus
The ''Opus Majus'' (Latin for "Greater Work") is the most important work of Roger Bacon. It was written in Medieval Latin, at the request of Pope Clement IV, to explain the work that Bacon had undertaken. The 878-page treatise ranges over all ...
'' ("Greater Work"), c. 1267
References
Further reading
* Segura, Wenceslao (2012)
''La reforma del calendario''
External links
(very brief mention in New York Times op-ed page) ()
in which each year has either 364 or 371 days
Historical information
{{Calendars
Proposed calendars
Reform