Calendars throughout History: An Overview of Calendar Systems around the World

This section provides information on calendars in various parts of the world and within major religious traditions. Following a general historical overview, these calendars will be discussed in the order in which they were developed or established.

Calendars throughout History: An Overview

The calendar is so ordinary, and yet so important, that one can hardly imagine a time when it did not exist. It is a fundamental commodity of life. Its significance is so great that in some cultures the institution and maintenance of dating systems have sacred status, and they fall under the jurisdiction of religious authorities.
Around the globe, through centuries of human history, a wide range of different calendars have been used to order time in a systematic manner—a need that all human civilizations share. Today, the Western Gregorian calendar serves as an international standard for business and diplomatic purposes. On the world’s stage, this is a recent development, and people of various religions, nations, and societies still employ many other calendars to mark the passing of time. The characteristics of these calendars are as diverse as the societies that developed them. All calendars, however, serve the common purpose of enabling people to work together to accomplish specific goals.
In the broadest sense, a calendar consists of the set of rules that a society uses to determine which days are ordinary and which are days are holy, or holidays.
Thousands of years ago, before the beginning of the written historical record, people lived in small tribal societies based on hunting and gathering. Activities were likely coordinated by word of mouth, and time-keeping methods were fairly uncomplicated. People probably used days as indications of time, and perhaps they even recognized periods similar to months through observing changes in the moon’s appearance. They would have observed seasonal and annual patterns, but without a formal system of reckoning them. Almost certainly, their needs did not demand anything as complex as a decade or century.
Over the course of time, people began living in agricultural communities with larger populations and diversified work forces. This shift required that people become more interdependent. For example, if farmers and city dwellers were going to conduct business efficiently, they must come to the marketplace at the same time. As a result, the need for a tool to arrange societal events became apparent.

Ancient Egyptians and Babylonians Systematize Their Calendars

The first two cultures that influenced the development of the Western Gregorian calendar were the Babylonians and Egyptians. Both shared similar characteristics—an agricultural base, a large population spread over a significant expanse of land, and a need to gather together at regular intervals to observe religious festivals. The responsibility for forming a central time-reckoning system so that people would know when to arrive at these festivals was placed in the hands of the respective religious communities.
To develop their calendars, both groups followed similar approaches. They divided time into three major divisions—what we now recognize as days, months, and years—and then went about calculating the exact duration of each category. The questions faced by the ancient Babylonians and Egyptians were the same questions all subsequent calendar makers have had to address:
How long is a day?
How long is a month?
How long is a year?
These values may seem obvious to a modern observer, but it took centuries of ongoing observations, measurements, and calculations to set them.

The Day

The basic building block of all calendars is the day. The length of the day is set by the amount of time in which the earth completes one rotation on its axis. During the fifth century B.C.E. (Before Common Era, which is equivalent to the term B.C.), the Babylonians divided this duration of time into 24 segments that we now know as hours. However, because accurate measurement of seconds and even minutes was not possible until the 16th century C.E. (Common Era, equivalent to A.D.), the length of those hours has not always been fixed.
The day was given scientific regularity only with the development of accurate clocks, the demand for which was a byproduct of the interest in maritime navigation that came with the Renaissance.

The Month

A lunar month, the period of a complete cycle of the phases of the moon, lasts approximately 29.5 days, is easy for all to recognize, short enough to be counted without using large numbers, matches closely with the female menstrual cycle and, given its relation to the tidal cycle, also matches the duration of cyclic behavior in some marine animals. Its simplicity and minimal ease of observation (if one discounts cloudy skies) led to its great significance, and it was widely used as the basis for calendars in many cultures. The length of each month varied according to the culture. For example, the Babylonians alternated between 29- and 30-day months, while the Egyptians fixed them at 30 days.
The Seasons and the Year
But the problem inherent in the use of a lunar calendar is that the cycles of the sun, not the moon, determine the seasons, the predictability of which is essential to the success of agriculture. The seasons could be determined by solar observation, either by measuring the cycle of the midday shadow cast by a stick placed vertically in the ground, or by sophisticated astronomical calculations. Either system resulted in a solar year of approximately 365 days, incompatible with the 12 lunar months, each with 29.5 days, that resulted in a 354-day year.
Civilizations attempted to reconcile lunar months with the solar year in varied ways. The most influential ancient effort was that of the Egyptian astronomers. Working from precise mathematical observations and borrowing from Babylonian astronomy, they drew up the Roman calendar that Julius Caesar introduced.
Perhaps the most difficult issue faced by calendar makers was establishing the length of the year. Although measuring a complete cycle of seasons may not seem complicated, it created significant problems for many calendar systems.
Each season in a cycle was marked by weather changes. Some seasons were warm, others cold; some had high levels of precipitation, others low. This cycling of the seasons originally defined the year—a period of time important to agrarian cultures that depended heavily on the ability to predict optimal planting and harvesting times.
Each season contained several new moons or months. The cycling of the moon and the cycling of weather patterns were not synchronized. This led to different systems for measuring a year’s length.

Babylonians and Egyptians Disagree

In the fifth century B.C.E., the Babylonians and Egyptians both arrived at a specific number of days in the year, but their conclusions were different. The Babylonians claimed that the year was 360 days long while the Egyptians more accurately estimated the year at 365 days. The discrepancy between the two lengths of the year is puzzling.
One possibility for the difference is that the Babylonians simply miscalculated. This is unlikely, however, in light of their sophisticated astronomical and mathematical systems. Another explanation is that they rounded their figure from 365 to 360 to facilitate the interaction of the year with their base-12 numerical system.
The problem with the Babylonians’ five-day omission was that the months would not stay in line with the seasons of the year. Each year the beginning of each month would occur at least five days earlier in relation to the position of the sun. Eventually, the months would be completely dissociated with the seasons in which they originally occurred. To correct this problem, the Babylonians periodically added months to the calendar, a process termed intercalation, which can also be used to add “leap” days or weeks.
The Babylonians were not the only people to face the problem of keeping the months coordinated with the seasons. Even though the Egyptians calculated the length of the year more accurately, they too realized that their determination was not exactly perfect.

The Solar System Affects the Length of the Year

Precise division of a year into months or days is impossible because the seasons, the phases of the moon, and the ever-cycling periods of daylight and nighttime are determined by the earth’s relationship to the sun and the moon. The movements of these heavenly bodies do not neatly coincide with the mathematical systems of any human civilization.
The quest to discover the secrets of how the universe fits together has motivated astronomers throughout history. In the second century C.E., Ptolemy, a Greek astronomer, formulated the theory that the earth was the center of the universe and that the sun, stars, moon, and other planets revolved around it. In the 15th century C.E., the Polish astronomer Copernicus advocated the notion that the earth rotated on an axis and, along with the other heavenly bodies in the solar system, revolved around the sun. Shortly after the Copernican assertion, Galileo presented supporting evidence based on observations he had made using his invention, the telescope.

The Gap between the Lunar and Solar Cycles

We now understand that an 11.25-day difference exists between the 354-day lunar cycle on which the months are based and the 365.25-day solar cycle that determines the seasons. Calendar systems have applied three main strategies in their search for a solution to this discrepancy.
The first, called a lunar calendar, ignores the seasons and allows the lunar (moon) cycle to be the basis of the year, as the Islamic calendar does. A second is called a lunisolar calendar. It involves an elaborate system of calculations to add days or months to the lunar year until it coincides with the solar year. The Jewish calendar is one example. The third system, which originated with the Egyptians, is the pure solar calendar. It allows the sun to determine not only the seasons but the length of the months as well.

Chinese Calendar

The Chinese calendar, widely used in Asian countries, is based on the oldest system of time measurement still in use, with its origin believed to be 2953 B.C.E. Part of the reason that the Chinese calendar has survived intact for so long is that, until the middle of the 20th century, the document was considered sacred. Any changes to the calen­dar were tightly controlled by imperial authorities, and the penalty for illegally tampering with the time-keeping system was death. Until the rise of Communism in China during the 20th century, the official calendar was pre­sented to the emperor, governors, and other dignitaries in an annual ceremony. Since 1912, the Gregorian calendar has been in use for civic purposes.
The Chinese New Year takes place on the new moon nearest to the point that is defined in the West as the 15th degree of the zodiacal sign of Aquarius. Each of 12 months in the Chinese year is 29 or 30 days long and is divided into two parts, each of which is two weeks long. The Chinese calendar, like all lunisolar systems, requires periodic adjustment to keep the lunar and solar cycles integrated, therefore an intercalary month is added when necessary.
The names of each of the 24 two-week periods sometimes correspond to festivals that occur during the period. Beginning with the New Year, which takes place in late January or early February, these periods are known by the following names: Spring Begins (New Year), the Rain Water, the Excited Insects, the Vernal Equinox, the Clear and Bright, the Grain Rains, the Summer Begins, the Grain Fills, the Grain in Ear, the Summer Solstice, the Slight Heat, the Great Heat, the Autumn Begins, the Limit of Heat, the White Dew, the Autumnal Equinox, the Cold Dew, the Hoar Frost Descends, the Winter Begins, the Little Snow, the Heavy Snow, the Winter Solstice, the Little Cold, and the Great Cold.

Calendars of India

Throughout its history, India has used a plethora of calendars and dating systems, which have included two basic types: a civil calendar that changed with each new regime and a religious calendar maintained by the Hindus. Although each geographical region had its own Hindu calendar, most of the calendars shared some elements that they gleaned from a common heritage.

India’s Original Calendar

India’s first time-reckoning system emerged before 1000 B.C.E. It was based on astronomical observations and con­sisted of a solar year of 360 days comprising 12 lunar months. The discrepancy between the length of the solar and lunar years was corrected by intercalating a month every 60 months.
In 1200 C.E., the Muslims brought the use of their calendar to India for administrative purposes, and in 1757 the British introduced the Gregorian calendar. Even so, each separate state maintained a calendar that its citizens used in their daily interactions. Throughout India’s colonial days, the entrenchment of these local calendars created havoc for the central government because any given date would yield up to six different interpretations through­out the country. The difficulties continued as an indigenous government took control in 1947.

The Saka Era Calendar

When India became a unified and independent nation, the differences among regional calendars included more than 30 methods for determining the beginning of the era, the year, and the month. These variations in the Hindu calendar were the culmination of nearly 3,000 years of history.
In 1952, the Calendar Reform Committee was established and charged with task of devising a unified system that would adhere to modern astronomical calculations and accommodate the calculation of dates for religious festi­vals. As a result of the committee’s work, the National Calendar of India was adopted in 1957.
The National Calendar of India is a 12-month lunisolar calendar with traditional Hindu month names. Some months are 30 days in length; others are 31 days. The year is 365 days long, with an extra day added to the end of the first month every four years (coinciding with leap years in the Gregorian calendar).
The National Calendar of India counts years from the inception of the Saka Era (S.E.)—the spring equinox in 79 C.E. In the year in which it was adopted, the first day of the first month (Caitra) was Caitra 1, 1879 S.E., which corre­sponded to March 22, 1957 C.E. Using the Gregorian calendar for comparison, the year 1926 in the Saka Era began on March 22, 2004 C.E.
Dates for religious festivals, which depend on lunar and solar movements, are calculated annually by the India Meteorological Department, although regional variations still exist. For administrative purposes, the Indian gov­ernment currently follows the Gregorian calendar.

Hindu Calendar

Although each geographical region of India has had its own calendar, all are based on an ancient calendar, the ear­liest time measurement system in India, found in texts thought to date from as early as 1000 B.C. Of the multitudi­nous regional Hindu calendars, used only for religious holidays, the majority divide an approximate solar year of 360 days into 12 months. Each day is 1/30th of a month, with the intercalation of a leap month every 60 months. Time measurements based on observations of the constellations are used along with the calendar. Each month is divided into two fortnights: krsna (waning or dark half) and sukla (waxing or bright half). In southern India, the month begins with the new moon. In other parts of the country, the full moon is considered to be the beginning of the month. Many references to the Hindu calendar (depending on the source) are given as follows: month, fort­night (either S=waxing or K=waning), and number of the day in that fortnight, e.g., Rama Navami: Caitra S. 9.
The names of the Hindu months (with variant spellings) are given below, with the Burmese name for the month in brackets:
Caitra or Chaitra [Tagu]: March-April
Vaisakha [Kasone]: April-May
Jyeshta or Jyaistha [Nayhone]: May-June
Ashadha or Asadha [Waso]: June-July
Sravana [Wagaung]: July-August
Bhadrapada [Tawthalin]: August-September
Asvina [Thadingyut]: September-October
Kartika or Karttika [Tazaungmone]: October-November
Margasirsa or Margashirsha [Nadaw]: November-December
Pausa or Pausha [Pyatho]: December-January
Magha [Tabodwei]: January-February
Phalguna [Tabaung]: February-March

Jain Calendar

The Indian calendars generally have lunar months, but the duration of an average year is a sidereal year. The dates of most all the Jain festivals are calculated using such a lunisolar calendar. In northern India, the beginning of the month occurs at the full moon. This means that the first fortnight is waning. People in southern India typically mark the beginning of the month at the new moon and the first fortnight is waxing. Jains begin the new year in the autumn with the Diwali festival commemorating the liberation (achievement of Nirvana) of their founder, Nat­aputta Mahavira. The Hindu new year generally occurs in the spring; however, in Gujarat, the Hindu new year also starts with Diwali.)
Mahavira’s achievement of Nirvana (at his death) in 527 B.C.E. also serves as the epoch for the Jain calendar. Diwali 2004 C.E., for example, begins the year 2531 V.N.S. (Vira Nirvana Samvat).

Cyclical Eras

The Jain concept of how time cycles through progressive and regressive eras also differs from the Hindus’. Jains believe that a complete cycle of time consists of twelve separate units. Of these, six represent deteriorating condi­tions and six represent improving conditions. The third and fourth units of both half-cycles represent times when neither extreme predominates. Only during these units can the Tirthankaras be born.
Currently, the earth is experiencing the fifth unit in the declining part of the time cycle. Risabha, the first Tirthankara of the current age, is said to have been born during the third unit; Mahavira was born at the close of the fourth. Each of the last two units in the declining half-cycle has a duration of 21,000 years.
The months of the Jain calendar are given below. The names of the Jain months are nearly the same as those of the Hindu months, but the Jain new year begins in Kartika, rather than in Caitra.
Kartika: October-November
Margasira: November-December
Pausa: December-January
Magha: January-February
Phalguna: February-March
Caitra: March-April
Vaisakha: April-May
Jyestha: May-June
Asadha: June-July
Sravana: July-August
Bhadrapada: August-September
Asvina: September-October

Buddhist Calendar

The Buddhist calendar, which originated in India, varies among different geographic locations, as does the Hindu calendar, with which it shares many common elements. Buddhism spread outside India after the Buddha’s death in 483 B.C.E. The method for determining the date of the new year is not uniform among Buddhist sects. Therava­da Buddhists (those primarily in Sri Lanka, Laos, Burma/Myanmar, Thailand, and Cambodia), using a Hindu cal­endar as their basis, calculate the months by the moon and the new year by the sun’s position in relation to the twelve segments of the heavens, each named for a sign of the zodiac. The solar new year begins when the sun enters Aries, usually between April 13th and 18th. The lunar months alternate between twenty-nine and thirty days in length. The first lunar month is usually sometime in December, except for the Burmese Buddhist calendar, which begins in April (see Hindu Calendar above for Burmese names). Periodically, the seventh month has an intercalary day, and an intercalary month is added every few years. Cambodia, Laos, and Thailand refer to the months by number. Tibetan Buddhists, whose calendar has been heavily influenced by the Chinese calendar, begin their new year at the full moon nearest to the midpoint of Aquarius. Mahayana Buddhists (those primarily in Tibet, Mongolia, China, Korea, and Japan) base their holidays on Buddhist, Chinese, or Gregorian calendars.

Sikh Calendar

The Sikh calendar dates from the religion’s inception in the 15th century C.E. It is a lunar calendar that is based on the moon’s movement from one zodiac sign into the next rather than on the phase of the moon. The dates of some festivals, however, derive from the phase of the moon. The beginning of a new month is called the Sangrand. It is announced in the Sikh house of worship (gurdwara) but it is not a festival day.
Sikh festivals are marked on a special calendar called the Sikh Gurpurab Calendar. A gurpurab is a date commem­orating births, deaths (and martyrdoms), or other important events associated with the lives of the 10 Sikh human Gurus or with the Sikh scriptures, the Guru Granth Sahib. The Gurpurab Calendar also notes the anniversary dates of historic incidents important to the Sikh faith.
The Sikh Gurpurab Calendar begins with the month of Chait (March/April), showing its inspiration from the Hindu calendar. The Sikh New Year celebration, however, falls on the first day of the second month, Basakh.
The Sikh have used several calendars since their religious tradition began in the 15th century. Over time, the lunar calendar, called the Bikrami calendar, was used predominantly. The Bikrami calendar consisted of 12 months aver­aging 29.5 days. This yields a year that is approximately 11 days shorter than the solar year. To keep the lunar cal­endar in line with the solar seasons, the Sikh calendar intercalated an extra lunar month whenever two new moons occur within the same solar month. The 13th lunar month then took the name of the solar month in which it fell. The names of the regular 12 lunar months are listed in the Guru Granth Sahib.
The solar component of the Bikrami calendar, however, did not correspond exactly to the natural solar year—every 70 years a discrepancy equal to one day accrued. To resolve this problem, two calendars were developed to accu­rately match the natural solar year: the Nanakshai Calendar, which is based on Guru Nanak’s birth, and the Khal­sa Calendar, which is based on the founding of the Khalsa. In 1999 C.E., the Sikhs adopted the Nanakshai Calen­dar. Although the choice generated some controversy, it is now used to observe all Sikh religious holidays, and has grown increasingly popular, especially among Sikh communities outside India.
The Nanakshai calendar is devised in a manner that maintains consistency with the western Gregorian calendar so that holidays always fall on the same day of the year. It begins with the month of Chait (Chait 1 falls on March 14) and contains five months of 31 days and seven months of 30 days. The last month usually contains 30 days, but in leap years, an extra day is added.
The Nanakshai calendar counts years from Guru Nanak’s birth in 1469 C.E. The year 536 Nanakshai began in the year 2004 C.E.
The months of the Nanakshai calendar, along with variant spellings, are given below.
Chait or Chet: March-April
Basakh or Vaisakhi: April-May
Jaith or Jeth: May-June
Har or Harh: June-July
Sawan: July-August
Bhadro or Bhadon: August-September
Asun or Asu: September-October
Katik: October-November
Magar or Maghar: November-December
Poh: December-January
Magh: January-February
Phagan or Phagun: February-March

Mayan and Aztec Calendars

The Mayan and Aztec civilizations both used what is commonly referred to as the Mesoamerican calendar. This ancient calendar may have derived from the Olmec civilization, which thrived between 1300 and 400 B.C.E. in what is now southeastern Mexico, along the Gulf. The Mesoamerican calendrical system, which probably originated between 1000–900 B.C.E., employed not just one calendar, but a system of two interconnecting calendars: a 260-day calendar and a 365-day calendar. These two calendars ran alongside each other. Every 52 years, a named day from the 260-day calendar would be the same as a named day from the 365-day calendar (there are 18,980 days in 52 years, and 18,980 is the least common multiple of both 365 and 260). This 52-year cycle was observed by both the Mayans and the Aztecs.
Mayan civilization, in what is now southeastern Mexico, Belize, and portions of Guatemala and Honduras, flour­ished between about 300–900 C.E., a period known as the Classical Mayan era. The Mayans used the 260-day calen­dar—known as the tzolkin—for sacred purposes, and the 365-day solar-based calendar—called the haab—for agricul­tural purposes. The Mayan calendar system employed glyphs, small pictorial inscriptions, to represent such time periods as a day, a month, and a year, as well as to represent specific months of the year and specific days in the months. Each day was named for a god who was thought to be manifest as that day. The days’ numbers were writ­ten using a combination of dots and bars. The 260-day Mayan calendar was divided into 13 months of 20 named days. The 365-day calendar was divided into 18 months of 20 named days plus a brief month of five days, called Uayeb, or “ominous days.” The 52-year Mayan cycle is known as the Calendar Round. The 260-day system is thought to be the only one of its kind in the world. Scholars are not certain what the significance of 260 is, though some have noted that the average duration of human pregnancy is approximately 260 days long. In addition, the Mayans had a highly developed knowledge of astronomy, and 260 was a number significant in calculating the appearance of Venus—the planet identified with the Mayan god Kukulcán, known as Quetzalcoatl to the Toltec people, who flour­ished in Mesoamerica (and dominated the Mayans) from the 10th century to the middle of the 12th century.
Mayans also developed the Long Count, an extensive system of time-reckoning which attempted to encompass the time of the world from its creation to its end. The Mayans are thought to have developed the Long Count between 400 B.C.E. and 100 A.D. From this system, they dated the current creation to have occurred in 3114 B.C.E.(or 3113 B.C.E., by some contemporary calculations). This Long Count, according to some scholars, will end in Decem­ber 2011 (or 2012).
The Aztecs—they called themselves Mexica—dominated Mesoamerica after the Toltec empire collapsed, from the early 1300s up until the Spanish began colonization in the early 1600s. Like the Mayans, the Aztecs used the 260­day calendar divided into 13 months of 20 days; they called it tonalpohualli, or “count of day.” Their 365-day cal­endar also consisted of 18 months of 20 days plus a period of five days, which the Aztecs believed to be unlucky. The Aztecs also named their days after deities, but, unlike the Mayan system, Aztec numerical notation consisted only of dots. Aztecs probably did not use a Long Count. At the end of their 52-year cycle—which they called xiuh­molpilli, or “year bundle”—the Aztecs celebrated the new beginning with a great renewal ceremony (see NEW FIRE CEREMONY).
Today, the 365-day civil calendar predominates throughout the region, though some contemporary Mayans also continue to use the 260-day calendar to observe sacred festivals.

Babylonian Calendar

Babylonian, Sumerian, and Assyrian astronomers living in the Mesopotamian Valley hundreds of years B.C.E. developed calendars that would influence the later Roman Julian and Gregorian calendars. These calendars were based on the phases of the moon and were closely related to the religious life of the cultures that developed them. The influence of the Mesopotamian civilizations on the global art of calendar making was far-reaching because many of the techniques they developed were adopted by future societies.
Of the various cultures that thrived in the Mesopotamian valley, the Babylonians seem to have most significantly influenced calendar making. Many details of the evolution of the Babylonian calendar have been lost over the cen­turies, but it is known that the calendar was lunar in nature, had a system of intercalation, had months divided into seven-day units, and had days with twenty-four hours.
Because these early calendar makers were pioneers in the field, they were among the first to be confronted with the discrepancy between the lunar and solar cycles—a problem that had the potential to render any calendar sys­tem ineffective. To reconcile the two natural courses, the Babylonians worked out a schedule whereby an extra month was periodically intercalated. The process of intercalation, termed iti dirig, seems to have been rather arbi­trary at first, but by 380 B.C.E. a formal system was adopted adding an extra month in the third, sixth, eighth, eleventh, seventeenth, and nineteenth years. Many other cultures, including the Greeks, developed similar inter­calation schemes which may have drawn their inspiration from the Babylonian model.
Although the origin of the week has been a subject of much research and debate among scholars since the time of Plutarch (46-119 C.E.), most agree that the Babylonians are the primary source for the week in the Western civil cal­endar. Many researchers also conclude that the Babylonians devised the week as a part of their religious practices. They have observed that years, months, and days all reflect natural cycles, but the week does not. This observa­tion has led to some questions: Why does the week have seven days? Why are the days named after celestial bod­ies? Why are the days not arranged according to the order of the planets in the solar system? Many proposed solu­tions to these quandaries have surfaced over the course of time.
Details of the Babylonian calendar are few, but some are known. It appears that the major festival was the New Year celebration which took place in the spring of the year during the Babylonian month of Nisanu. On the first day of the festival, a ritual marriage was performed between the king and the high priestess, who symbolized the sovereignty of the land. On this day, the Babylonian creation myth (called Enuma elish from its opening words, “When on high”) was read aloud. On the fifth day, Rites of Atonement were observed. During the Rites the king, as a representative of the people, endured a ritual of abasement to atone for the sins of the people against the gods. On the seventh day, the Festival of the Sun, or spring equinox, took place.

Zoroastrian Calendars

Zoroastrianism originated in Iran. The religion’s founder Zoroaster, thought to have lived around 1200 B.C.E., con­verted a tribal Iranian prince, Vishtaspa. By the time of the Sasanian dynasty (226-651 B.C.E.), Zoroastrianism was the Persian state religion. After the Muslim conquest of Persia in the middle of the seventh century, many Zoroas­trians migrated to India, particularly the western state of Gujarat, where they became known as the “Parsi” (mean­ing “Persian”) community.
The Zoroastrian calendar derived from the ancient Babylonian calendar, except that the former’s days and months were dedicated to spiritual beings. In the mid-18th century, some Parsis adopted the Iranian calendar and called it the qadimi calendar, giving rise to the Zoroastrian sect known as Kadmi. Others remained with the traditional religion and calendar, though it was a month behind the Kadmi calendar, and were referred to as Shenshais, often rendered Shahanshahis. In 1906, the Fasli sect was founded. It advocated the use of a calendar closer to the Gre­gorian one, in which the new year would always begin at the vernal equinox and which would add an extra day every four years.
All three Zoroastrian calendars have the same twelve 30-day months with five intercalary days called Gatha com­ing at the end of the twelfth month. The differences are in how each reconciles the lunar year with the natural solar year. As a result, a single date on each Zoroastrian calendar corresponds to three different Gregorian dates. For example, in 2002, the first day of the first month (Frawardin 1) fell on March 21 according to the Fasli calendar, on July 22 according to the Kadmi calendar, and on August 21 according to the Shahanshai calendar.
The Zoroastrian month names and approximate English meanings are:
Frawardin or Fravardin (Humanity) March-April*
Ardwahist or Ardibehest (Truth and Righteousness) April-May
Hordad or Khordad (Perfection) May-June
Tir (Sirius, the Dog Star) June-July
Amurdad or Amardad (Immortality) July-August
Shahrewar or Sherever (Benevolent Dominion) August-September
Mihr or Meher (Fair Dealing) September-October
Aban or Avan (Water or Purity) October-November
Adar or Adur (Fire) November-December
Dae or Deh (Creator) December-January
Vohuman or Bahman (Good Mind) January-February
Spendarmad or Aspandarmad (Holy Devotion) February-March
* Gregorian month ranges corresponding to the Fasli calendar

Roman Julian Calendar

Julius Caesar ordered the change of the reformed Roman lunar calendar to a solar-based one in 46 B.C.E. The inter­calation of ninety days corrected a growing discrepancy between the seasons and the months in which they had traditionally fallen. Prior to this intercalation, the Roman civic year had come to be about three months “ahead” of the seasons, so spring began in June. The year 46 B.C.E. was assigned 445 days to make the adjustment; it was called ultimus annus confusionis, “the last year of the muddled reckoning.” The new calendar, based on the Egypt­ian solar calendar, provided for a year of 365 days with an additional day in February every fourth year. The addi-tion of this leap year and day gives the Julian year an average length of 365.25 days—very close to the actual solar cycle. The Julian calendar (O.S., or Old Style) remained in civic use in the West for more than 1,600 years, is still the basis of the “Old Calendarist” Orthodox Christian liturgical calendar, and is used by all Orthodox Christian churches to determine the date of Easter.

Jewish Calendar

In 358 C.E., Hillel II introduced a permanent calendar based on mathematical and astronomical calculations, eliminat­ing the need for eyewitness sightings of the new moon with which the new month begins. Due to doubts as to when the new moon appeared, biblical law stated that those living outside Israel would observe two days rather than one for each festival, except for Yom Kippur, the Day of Atonement. The Talmud required that this custom continue even after the calendar was formulated. The Jewish era begins with the date of Creation, traditionally set in 3761 B.C.E.
Only slight modifications were made to Hillel’s calendar, and it has remained unchanged since the tenth century. A day is reckoned from sundown to sundown, a week contains seven days, a month is either twenty-nine or thir­ty days long, and a year has twelve lunar months plus about eleven days, or 353, 354, or 355 days. To reconcile the calendar with the annual solar cycle, a thirteenth month of thirty days is intercalated in the third, sixth, eighth, eleventh, fourteenth, seventeenth, and nineteenth years of a nineteen-year cycle; a leap year may contain from 383 to 385 days. The civil calendar begins with the month of Tishri, the first day of which is Rosh Hashanah, the New Year. The cycle of the religious calendar begins on Nisan 15, Passover (Pesach).
The names of the months of the Jewish calendar were borrowed from the Babylonians. The pre-exilic books of the Bible usually refer to the months according to their numerical order, beginning with Tishri, but there are four months mentioned with different names: Nisan/Abib, Iyyar/Ziv, Tishri/Ethanim, and Heshvan/Bul:
Nisan: mid-March to mid-April
Iyyar: mid-April to mid-May
Sivan: mid-May to mid-June
Tammuz: mid-June to mid-July
Av: mid-July to mid-August
Elul: mid-August to mid-September
Tishri: mid-September to mid-October
Heshvan: mid-October to mid-November
Kislev: mid-November to mid-December
Tevet: mid-December to mid-January
Shevat: mid-January to mid-February
Adar: mid-February to mid-March
*The intercalary month of Adar II is inserted before Adar as needed.

Islamic Calendar

The Islamic calendar, called hijri or Hegirian, is still strictly lunar-based. Moreover, the actual beginning of a month depends on the sighting of the new moon. Traditionally, if the sky is overcast and the new moon is not visible, the previous month runs another thirty days before the new month begins. However, the practical beginning of a month is according to astronomical calculations of lunar cycles. The Islamic era begins July 16, 622 C.E., the date of the hegira or flight into exile of the Prophet Muhammad from Mecca to Medina.
There are twelve Islamic lunar months, some of twenty-nine, others of thirty days; these yield 354 days in the Islamic year. The fixed holidays set in the Islamic calendar thus move “backward” about ten days each year in rela­tion to the Gregorian calendar. In roughly thirty-six years, Ramadan, the Islamic holy month of fasting, moves back through the entire solar year. The Islamic day runs from sundown to sundown.
Other calendars were developed in Islamic countries for the sake of agriculture, which depends on a solar calen­dar. The Coptic calendar, a variation of the Julian, was used until recently, but is now limited primarily to Egypt and the Sudan, countries with large Coptic populations. The Turkish fiscal calendar, also Julian-based, was used in the Ottoman Empire. Nowadays, the Gregorian calendar is followed nearly everywhere for civic purposes, and the Islamic calendar determines only the days of religious observance. Saudi Arabia is one exception, and, at least officially, employs the Islamic calendar as the calendar of reference.
The names of the Islamic months are an ancient reflection of the seasons of the solar year:
Muharram: the sacred month
Safar: the month which is void
Rabi al-Awwal: the first spring
Rabi ath-Thani: the second spring
Jumada-l-Ula: the first month of dryness
Jumada-th-Thaniyyah: the second month of dryness
Rajab: the revered month
Shaban: the month of division
Ramadan: the month of great heat
Shawwal: the month of hunting
Dhu al-Qadah: the month of rest
Dhu al-Hijjah: the month of pilgrimage

Gregorian Calendar

By the late 16th century, the difference between the Julian calendar and the seasons had grown to ten days because the Julian year, averaging 365.25 days, was slightly longer than the actual length of a solar year, which, by mod­ern calculation, is known to be 365.242199 days long. Fixed holy days began to occur in the “wrong” season, both for the church and for farmers, who used certain holy days to determine planting and harvesting. Pope Gregory XIII ordered the reform that deleted ten days from the year 1582; in that year, October 15 was the day after Octo­ber 5. This change, coupled with the elimination of leap days in “century” years unless evenly divisible by 400 (e.g., 1600, 2000), corrected the calendar so that today only occasional “leap seconds” are needed to keep months and seasons synchronized. At first adopted only in Roman Catholic countries, the Gregorian calendar (N.S., or New Style) gradually came to be accepted throughout the West, and today has become the calendar used by most of the world, at least for business and government.

Christian Liturgical Calendars

Clearly visible within the Christian liturgical calendar are elements of both the Hebrew and Greek time-keeping systems. Most immediately recognizable, however, are the influences of the Jewish calendar. The movable feasts within Christianity, such as Easter and Pentecost, have connections to Hebrew celebrations.
Many branches of Christianity follow similar calendars to mark the holy days of the year. The calendar focuses attention on special incidents in Jesus’s life and also provides for the remembrance of many saints and historical events. It includes two types of dates: movable feasts, which are typically established based on their relationship to the Feast of the Resurrection (Easter), and fixed holidays.

Old and New Calendars

Throughout the centuries the Julian Calendar has been in use in both the Christian East and West. The introduc­tion of the Gregorian Calendar fueled the ever-accelerating animosity between the two Churches. Even though many in the East recognized the inadequacies of the Julian Calendar, leading some to go so far as to devise new calendars for themselves, it nevertheless remained in use throughout the Byzantine period and beyond.
With the introduction of the Gregorian Calendar, Pope Gregory tried to convince the Orthodox to adopt it, but the latter refused because it would alter the dating of Easter. Canon 7 of the Council of Nicea (325) set clear regula­tions for the dating of Easter. To adopt the Gregorian Calendar would mean having Easter coincide with the Jew­ish Passover, something clearly against the canonical stipulations.
Orthodox Churches continued to use the Julian Calendar until May of 1923 when the Ecumenical Patriarch Mele­tios IV convened an “Inter-Orthodox Congress” in Constantinople. Not all Orthodox Churches were represented. Though invited, the Churches of Alexandria, Antioch, and Jerusalem did not attend. The Church of Bulgaria was never asked. Only the Orthodox Churches of Cyprus, Greece, Romania, and Serbia participated. Even then, no unanimous decision was reached regarding the calendar of choice. It has been only in recent years that the Church­es of Alexandria, Antioch, Constantinople, Cyprus, Greece, Poland, Romania, and, in 1968, Bulgaria, voted to adopt the new Gregorian Calendar. The Churches of Jerusalem, Russia, and Serbia continue to adhere to the old Julian Calendar.

Western Liturgical Calendar

The western Christian liturgical year begins in late November with a season called Advent. Four weeks long, Advent provides a time during which Christians prepare for Jesus’s birth. Advent is followed by Christmas and the Christmas season during which Jesus’s birth is celebrated. Epiphany, in early January commemorates Jesus’s appearance to the Gentiles (non-Jews). Lent is a season of introspection and penance in preparation for Easter. It concludes with Holy Week, when events in the last week of Jesus’s life are highlighted. The Easter season begins on Resurrection Sunday and lasts until Ascension Day, commemorating Jesus’s ascension into heaven. The season of Pentecost begins with the celebration of the coming of the Holy Spirit. The longest season of the year, Trinity, completes the cycle.
The revised Roman Catholic calendar of 1969 changed some of the days on which certain saints were honored. Once universally honored days became only locally honored. According to Catholic law, followers are obligated to participate in Mass weekly on either a Saturday evening or Sunday morning and on six other days identified as holy days of obligation: Christmas, Solemnity of Mary, Ascension, Assumption of the Blessed Virgin, All Saints Day, and Immaculate Conception.

Orthodox Liturgical Calendars

In the Orthodox Church, two different calendars determine holidays and feast days. One, attributed to the Roman Emperor Julius Caesar, bears his name. The latter emerged in the 16th century as an effort to correct the discrep­ancy between calendar time and calculated astronomical time. It added 13 days back into the year and was named for Pope Gregory XIII, who commissioned the work.
There are five main elements to the Orthodox liturgical calendar: the daily cycle, the weekly cycle, the Paschal cycle, the cycle of fixed feasts, and the cycle of eight tones.
In contrast to practice in many other Christian Churches of starting the liturgical year with the first Sunday in Advent, the Orthodox liturgical year begins on September 1. In the Ecumenical Patriarchate this is observed as the Day of the Environment, with the role in the salvation of the world of the Theotokos, the mother of God, being emphasized. The Nativity of the Virgin Mary on September 8 and her Dormition on August 15 come at opposite ends of the liturgical year. Other than those included among the twelve great feasts, the other Marian feast day is December 9, the Conception of the Virgin by St. Anne.
March 25, the Annunciation, is another major feast of the Theotokos, but it is also a feast of the Conception of Christ and begins a series of feasts of the Lord. The Nativity of the Lord, as well as the Visit of the Magi, is observed in the Orthodox Church on December 25. The Circumcision of Jesus falls on January 1, the feast of Saint Basil the Great. For the Orthodox Christian, Epiphany, or Theophany as it is sometimes known, is January 6 and commem­orates Christ’s baptism. The feast of the Transfiguration is held on August 6.
The Paschal cycle begins four weeks before Lent, on the Sunday of the Pharisee and the Publican. Lent itself begins on Pure Monday and ends on Lazarus Saturday, the day before Palm Sunday. The Passion, the Mystical Supper, the Agony, Betrayal, Trial, Sufferings, Death, Burial and Glorious Resurrection, the Assumption into Heaven of the Lord, and the Sending of His Holy Spirit upon the Apostles are all celebrated in the feasts of the Paschal cycle. The cycle ends with Pentecost Sunday, the feast of the Holy Trinity, and the Sunday of All Saints.
In addition to the special feast days of the Lord or of Mary, every day on the Orthodox Calendar commemorates some saint. These may be saints venerated by all of Christendom, Latin Church saints from early centuries, saints particular to a specific locale, or the Righteous, or Dikaios, of the Old Law. Somewhat anachronistically, the Mac­cabees are commemorated as though they were Christian martyrs. The Maccabees were the family of Mattathias who, in 167 B.C.E., led the Jewish revolt against Antiochus IV Epiphanes. Even some Latin Church saints from after the Great Schism are recognized, and some Latin feasts, such as Corpus Christi, are observed.
In the medieval period of the Church, all music was organized on the basis of a system of eight tones. These tones continue to have not only musical significance but a calendrical significance as well. Beginning the first Sunday after Easter, St. Thomas Sunday, each successive week uses the texts and music of the next of the eight tones for its offices. Each day of the week has its distinctive hymns and verses for each of these eight tones. The book which contains the texts for each day’s services for all eight tones is called the Parakletike.

Baha’i Calendar

The Baha’i calendar, called the Badí (meaning “wondrous”), consists of 19 months, each with 19 days. Four inter­calary days—called AYYAM-I-HA, the Days of Ha—occur after the 18th month in regular years, while five are insert­ed in leap years. Nineteen multiplied by 19 equals 361, plus four intercalary days equals 365. But the number 19 was chosen for more than its mathematical convenience. The Baha’i religion’s first prophet, Mirza Ali Mohammad (also known as the BAB), devised a calendar for the new religion. He had 18 followers, thus these 19 original Babis are remembered in the calendar’s structure.
The 19-Day Feast takes place on the first day of each month and constitutes the regular Baha’i worship gathering. Each Feast follows the same three-part format: prayer, congregational business, and fellowship with a shared meal.
The Baha’i year begins on the vernal equinox, March 21. Baha’i years are numbered. Year 1 was 1844, the year of the Bab’s Declaration. Each Baha’i month is named for an attribute of God:
Bahá (Splendor) March 21
Jalál (Glory) April 9
Jamál (Beauty) April 28
Azamat (Grandeur) May 17
Núr (Light) June 5
Rahmat (Mercy) June 24
Kalimát (Words) July 13
Kamál (Perfection) August 1
Asmá (Names) August 20
‘Izzat (Might) September 8
Mashiyyat (Will) September 27
‘Ilm (Knowledge) October 16
Qudrat (Power) November 4
Qawl (Speech) November 23
Masá’il (Questions) December 12
Sharaf (Honor) December 31
Sultán (Sovereignty) January 19
Mulk (Dominion) February 7
Ayyam-i-Ha (Days of Ha; intercalary days): February 26-March 1 (February 26-March 2 in leap years)
‘Alá’ (Loftiness) March 2 (month of fasting)
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