Here is the full Calendar Systems around the World: Julian calendar, Gregorian calendar, Jewish, Islamic calendar, Hindu, Buddhist, Chinese, Mayan and Aztec, Baha’i, and Zoroastrian calendar. The names, meaning and brief history of origins of days and month of each.

What is a Calendar?

A calendar is a means of reckoning time through the application of divisions—days, weeks, months, and years. Some of these divisions, such as months, originate in observations of phenomena in nature. Others, such as weeks, are quite arbitrary. In primitive times, people reckoned by cycles of the moon (months), but when a more convenient, shorter period was needed days were grouped, e.g., intervals between market days probably led to the use of the seven-day week. The originally Jewish seven-day week became a standard throughout Western civilization starting from the third century B.C.

The Day

The day is a fairly natural division, despite the variation in the length of sunlight through the year. The Babylonians introduced divisions of the day into twenty-four hours, but the length of hours varied through the year. 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, was the day given scientific regularity.

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, with 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, e.g., the Babylonians alternated between twenty-nine and thirty-day months, the Egyptians fixed them at thirty days, etc.

The Seasons

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 twelve 29.5-day lunar months that resulted in a 354-day year. Civilisations 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, who drew up the Roman calendar that Julius Caesar introduced.

Julian Calendar

Julius Caesar ordered the change of the reformed Roman lunar calendar to a solar-based one in 46 B.C. The intercalation of ninety days corrected a discrepancy that had been growing 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. 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 addition 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.

Gregorian Calendar

By the late sixteenth 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 synchronised. 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.

Jewish Calendar

In 358, 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 of 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. Only slight modifications were made to Hillel’s calendar, and it has remained unchanged since the tenth century. Aday 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 preexilic 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
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  • 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, 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 use in 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, uses 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
  • 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 twelve months. Each day is 1/30th of a month, with the intercalation of a leap month every sixty 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
  • Buddhist Calendar

    The Buddhist calendar originated in India and varies among different geographic locations, as does the Hindu calendar, with which it shares many common elements. 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. 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.

    Chinese Calendar

    The Chinese calendar, widely used in Asian countries, is based on the oldest system of time measurement still in use, with its epoch believed to be 2953 B.C.Part of the reason that the Chinese calendar has survived intact for so long is that, until the middle of the twentieth 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 twentieth 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 which is defined in the West as the fifteenth degree of the zodiacal sign of Aquarius. Each of twelve months in the Chinese year is twenty-nine or thirty 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 twenty-four two-week periods sometimes correspond to festivals which 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.

    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.in what is now southeastern Mexico, along the Gulf. The Mesoamerican calendrical system probably originated between 1000–900 B.C. and 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 A.D., 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.and 100 A.D.From this system, they dated the current creation to have occurred in 3114 B.C. (or 3113 B.C., by some contemporary calculations). This Long Count, according to some scholars, will end in December 2011 (or 2012). The Aztecs (they called themselves Mexica) were dominant in 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 260-day 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. 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.

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    Baha’i Calendar

    The Baha’i calendar, called the Badí (meaning “wondrous”), is made up of nineteen months, each with nineteen days. Four intercalary days — called A YYAM-I-HA, the Days of Ha—occur after the eighteenth month in regular years, while five are inserted in leap years. Nineteen multiplied by nineteen equals 361, plus four intercalary days equals 365. But the number nineteen 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 eighteen followers, thus these nineteen original Babis are remembered in the calendar’s structure. The Nineteen-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)
  • Zoroastrian Calendars

    Zoroastrianism originated in Iran. The religion’s founder Zoroaster is thought to have lived around 1200 B.C. He converted a tribal Iranian prince Vishtaspa and by the time of the Sasanian dynasty (226-651 A.D.), Zoroastrianism was the Persian state religion. In response to 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-eighteenth 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, which 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
  • NOTE: Gregorian month ranges corresponding to the Fasli calendar