Solar calendar

A solar calendar is a calendar whose dates indicate the season or almost equivalently the apparent position of the Sun relative to the stars. The Gregorian calendar, widely accepted as standard in the world, is an example of a solar calendar. The main other type of calendar is a lunar calendar, whose months correspond to cycles of Moon phases. The months of the Gregorian calendar do not correspond to cycles of Moon phase.


The oldest solar calendars include the Julian calendar and the Coptic calendar. They both have a year of 365 days, which is extended to 366 once every four years, without exception, so have a mean year of 365.25 days. As solar calendars became more accurate, they evolved into two types.

Tropical solar calendars

If the position of the Earth in its orbit around the Sun is reckoned with respect to the equinox, the point at which the orbit crosses the celestial equator, then its dates accurately indicate the seasons, that is, they are synchronized with the declination of the Sun. Such a calendar is called a tropical solar calendar.

The duration of the mean calendar year of such a calendar approximates some form of the tropical year, usually either the mean tropical year or the vernal equinox year.

The following are tropical solar calendars:

Every one of these calendars has a year of 365 days, which is occasionally extended by adding an extra day to form a leap year, a method called "intercalation", the inserted day being "intercalary".

The Baha'i calendar always begins the year on the vernal equinox and sets its intercalary days so that the following year also begins on the vernal equinox. The moment of the vernal equinox in the northern hemisphere is determined as at Tehran "by means of astronomical computations from reliable sources".[1] °

Sidereal solar calendars

If the position of the Earth (see above) is reckoned with respect to the fixed stars, then the dates indicate the zodiacal constellation near which the Sun can be found. A calendar of this type is called a sidereal solar calendar.

The mean calendar year of such a calendar approximates the sidereal year.

Indian calendars like the Hindu calendar, Tamil calendar, Bengali calendar (non-revised) and Malayalam calendar are sidereal solar calendars. The Thai solar calendar, when based on the Hindu solar calendar was also a sidereal calendar. They are calculated on the basis of the apparent motion of the Sun through the twelve zodiacal signs rather than the tropical movement of the Earth.

Non-solar calendars

The Islamic calendar, which is a purely lunar calendar and has a year, whose start drifts through the seasons and so is not a solar calendar. The Maya Tzolkin calendar, which follows a 260-day cycle, has no year, so is not a solar calendar. Also any calendar calendars synchronized only to the synodic period of Venus would not be solar.

Lunisolar calendars

Lunisolar calendars may be regarded as solar calendars, although their dates additionally indicate the Moon phase. Because a typical lunisolar calendar has a year made up of a whole number of lunar months, it can't indicate the position of Earth on its revolution around the Sun as well as a pure solar calendar can.

List of solar calendars

See also


  1. ^ The Universal House of Justice (2014-07-10). "To the Bahá'ís of the World". Retrieved 2014-07-10.

External links

Aries (astrology)

Aries (♈) (meaning "ram") is the first astrological sign in the zodiac, spanning the first 30 degrees of celestial longitude (0°≤ λ <30°). Under the tropical zodiac, the Sun transits this sign from approximately March 20 to April 21 each year. This time duration is exactly the first month of the Solar Hijri calendar (Hamal/Farvardin/Wray). The symbol of the ram is based on the Chrysomallus, the flying ram that provided the Golden Fleece.According to the tropical system of astrology, the Sun enters the sign of Aries when it reaches the March equinox, which occurs on average on March 21 (by design). Because the Earth takes approximately 365.24 days to go around the Sun, the precise time of the equinox is not the same each year, and generally will occur about six hours later from one year to the next until reset by a leap year. February 29 of a leap year causes that year's vernal equinox to fall about eighteen hours earlier compared with the previous year. From 1800 to 2050 inclusive the vernal equinox date has (or will) range(d) from March 19 at 22:34 UT1 in 2048 to March 21 at 19:15 UT1 in 1903.Under the sidereal zodiac, the sun currently transits Aries from April 15 to 14 May (approximately).

Aries is the first fire sign in the zodiac, the other fire signs being Leo and Sagittarius. Individuals born between these dates, depending on which system of astrology they subscribe to, may be called Arians or Ariens.The equivalent in the Hindu solar calendar is Meṣa.


Ashwin or Ashvin or Ashwan (; Nepali: आश्विन , असोज, Bengali: আশ্বিন; Hindi: अश्विन; Malay/Indonesian: Aswin; Thai: Asawin), also known as Aswayuja, is the seventh month of the lunisolar Hindu calendar, the Vikram Samvat, which is the official solar calendar of Nepal and the parts of India. It is the sixth month in the solar Bengali calendar and seventh in the lunar Indian national calendar of the Deccan Plateau. It falls in the season of Shôrot, (Hindi Sharad) or Autumn. In Vedic Jyotish, Ashwin begins with the Sun's enter in Virgo.

It overlaps September and October of the Gregorian calendar and is the month preceding Diwali or Tihar the festival of lights. In lunar religious calendars, Ashwin begins on the new moon after the autumn equinox.

Assyrian calendar

The Assyrian calendar is a solar calendar used by modern Assyrians. The year begins with the first sight of Spring. 4750 BC was set as its first year in the 1950s, based on a series of articles published in the Assyrian nationalist magazine Gilgamesh, edited by the brothers Addi Alkhas and Jean Alkhas and Nimrod Simono. The Assyrian new year is still celebrated every year with festivals and gatherings. As of April 2019 AD, it is the 6769th year of the Assyrian calendar, and this calendar is used among many Assyrian communities.

It begins 4,750 years before the Gregorian calendar. For example, it is set out like this: 2019+4750 = Assyrian year 6769.

The Assyrian month names are also used in the Arabic Gregorian solar calendar in the Levant and Mesopotamia (Iraq, Jordan, Lebanon, Palestine, Syria).

Bengali calendars

The Bengali Calendar or Bangla Calendar (Bengali: বঙ্গাব্দ, lit. 'Baṅgābda') is a luni-solar calendar used in the Bengal region of the Indian subcontinent. A revised version of the calendar is the national and official calendar in Bangladesh and an earlier version of the calendar is followed in the Indian states of West Bengal, Tripura and Assam. The New Year in the Bengali calendar is known as Pohela Boishakh.

The Bengali era is called Bengali Sambat (BS) or the Bengali year (বাংলা সন Bangla Sôn, বাংলা সাল Bangla sal, or Bangabda) has a zero year that starts in 593/594 CE. It is 594 less than the AD or CE year in the Gregorian calendar if it is before Pôhela Bôishakh, or 593 less if after Pôhela Bôishakh.

The revised version of the Bengali calendar was officially adopted in Bangladesh in 1987. Among the Bengali community in India, the traditional Bengali Hindu calendar continues to be in use, and it sets the Hindu festivals.

Buddhist calendar

The Buddhist calendar is a set of lunisolar calendars primarily used in mainland Southeast Asian countries of Cambodia, Laos, Myanmar and Thailand as well as in Sri Lanka and Chinese populations of Malaysia and Singapore for religious or official occasions. While the calendars share a common lineage, they also have minor but important variations such as intercalation schedules, month names and numbering, use of cycles, etc. In Thailand, the name Buddhist Era is a year numbering system shared by the traditional Thai lunisolar calendar and by the Thai solar calendar.

The Southeast Asian lunisolar calendars are largely based on an older version of the Hindu calendar, which uses the sidereal year as the solar year. One major difference is that the Southeast Asian systems, unlike their Indian cousins, do not use apparent reckoning to stay in sync with the sidereal year. Instead, they employ their versions of the Metonic cycle. However, since the Metonic cycle is not very accurate for sidereal years, the Southeast Asian calendar is slowly drifting out of sync with the sidereal, approximately one day every 100 years. Yet no coordinated structural reforms of the lunisolar calendar have been undertaken.

Today, the traditional Buddhist lunisolar calendar is used mainly for Theravada Buddhist festivals, and no longer has the official calendar status anywhere. The Thai Buddhist Era, a renumbered Gregorian calendar, is the official calendar in Thailand.


Chaitra is a month of the Hindu calendar.

In the standard Hindu calendar and India's national civil calendar, Chaitra is the first month of the year. It is the last month in the Bengali calendar, where it is called Choitro. Chaitra or Chait is also the last month in the Nepali calendar (the Vikram Samvat), where it commences in mid-March. Chithirai is the first month in the Tamil calendar. In Sindhi calendar, this month is referred to as Chet and is marked by celebration of the Cheti Chand (birth of Jhulelal, an incarnation of Vishnu). In the Vaishnava calendar, Vishnu governs this month.

In the more traditional reckoning, the first month commences in March or April of the Gregorian Calendar, depending upon whether the Purushottam Maas (extra month for alignment of lunar or solar calendar) was observed in the year. There is no fixed date in Gregorian calendar for 1st day of Chaitra, i.e., the beginning of the Hindu New Year.

Indian New Year's days

There are numerous days throughout the year celebrated as New Year's Day in the different regions of India. Observance is determined by whether the lunar calendar is being following or the solar calendar. Those regions which follow the Solar calendar, the new year falls on Sankranti of the first month of the calendar, i.e., Vaishakha. Generally, this day falls during 14th or 15th of the month of April. Those following Lunar calendar consider the month of Chaitra (corresponding to March-April) as the first month of the year, so the new year is celebrated on the first day of this month. Similarly, few regions in India consider the period between consecutive Sankarantis as one month and few others take the period between consecutive Purnimas as a month.

Lunar calendar

A lunar calendar is a calendar based upon the monthly cycles of the Moon's phases (synodic months), in contrast to solar calendars, whose annual cycles are based only directly upon the solar year. The most commonly used calendar, the Gregorian calendar, is a solar calendar system that originally evolved out of a lunar calendar system. A purely lunar calendar is also distinguished from a lunisolar calendar, whose lunar months are brought into alignment with the solar year through some process of intercalation. The details of when months begin varies from calendar to calendar, with some using new, full, or crescent moons and others employing detailed calculations.

Since each lunation is approximately ​29 1⁄2 days (29 days, 12 hours, 44 minutes, 3 seconds, or 29.530588 days), it is common for the months of a lunar calendar to alternate between 29 and 30 days. Since the period of twelve such lunations, a lunar year, is only 354 days, 8 hours, 48 minutes, 34 seconds (354.367056 days), purely lunar calendars lose around 11 days per year relative to the Gregorian calendar. In purely lunar calendars like the Islamic calendar, the lack of intercalation causes the lunar months to cycle through all the seasons of the Gregorian year over the course of a 33 lunar-year cycle.

Although the Gregorian calendar is in common and legal use in most countries, traditional lunar and lunisolar calendars continue to be used throughout the Old World to determine religious festivals and national holidays. Examples of such holidays include Ramadan (Islamic calendar); Easter; the Chinese, Japanese, Korean, Vietnamese, and Mongolian New Year (Chinese, Japanese, Korean, Vietnamese, and Mongolian calendars); the Nepali New Year (Nepali calendar); the Mid-Autumn Festival and Chuseok (Chinese and Korean calendars); Loi Krathong (Thai calendar); Sunuwar calendar; Vesak/Buddha's Birthday (Buddhist calendar); Diwali (Hindu calendars); and Rosh Hashanah (Hebrew calendar).

Lunisolar calendar

A lunisolar calendar is a calendar in many cultures whose date indicates both the Moon phase and the time of the solar year. If the solar year is defined as a tropical year, then a lunisolar calendar will give an indication of the season; if it is taken as a sidereal year, then the calendar will predict the constellation near which the full moon may occur. As with all calendars which divide the year into months there is an additional requirement that the year have a whole number of months. In this case ordinary years consist of twelve months but every second or third year is an embolismic year, which adds a thirteenth intercalary, embolismic, or leap month.

Moveable feast

A moveable feast or movable feast is an observance in a Christian liturgical calendar that occurs on a different date (relative to the dominant civil or solar calendar) in different years.The most important set of moveable feasts are a fixed number of days before or after Easter Sunday, which varies by 35 days since it depends partly on the phase of the moon and must be computed each year. In Eastern Christianity (including the Eastern Orthodox Church, the Oriental Orthodox Churches, the Assyrian Church of the East, and the Eastern Catholic Churches), these moveable feasts form what is called the Paschal cycle, which stands in contrast to the approach taken by Catholic and Protestant Christianity.

Most other feast days, such as those of particular saints, are fixed feasts, held on the same date every year. However, some observances are always held on the same day of the week, and thus occur on a range of days without depending on the date of Easter. For example, the start of Advent is the Sunday nearest November 30. In addition, the observance of some fixed feasts may move a few days in a particular year to not clash with that year's date for a more important moveable feast. There are rare examples of saints with genuinely moveable feast days, such as Saint Sarkis the Warrior in the calendar of the Armenian Church.

Mystical Horizons

Mystical Horizons, located near Carbury, North Dakota on the Scenic Byway on North Dakota Highway 43 near the North Dakota and Manitoba border, is intended to represent a 21st-century Stonehenge. It consists of six pink granite walls of varying heights that also function as a working solar calendar. The structure was built in 2005.

A plaque (photo 1 in external links) reads "Dedicated to Jack Olson's vision of a Century 21 Stonehenge" and lists the building partnerships.

Punjabi calendar

The Punjabi calendar is used by the Punjabi people of the Indian subcontinent, but varies by religions. Historically, the Punjabi Sikhs and Punjabi Hindus have used the ancient Indian Bikrami (Vikrami) calendar, which started in 57 BCE with legendary Emperor Vikramaditya. Punjabi Muslims use the Arabic Hijri calendar. Some festivals in Punjab, Pakistan are determined by the Punjabi calendar, such as Muharram which is celebrated twice, once according to the Muslim year and again on the 10th of harh. The Bikrami calendar is the one the rural (agrarian) population follows in Punjab, Pakistan.In Punjab though the solar calendar is generally followed, the lunar calendar used is purnimanta. The lunar month is calculated from the ending moment of the full moon: the beginning of the dark fortnight. Chaitra is considered to be the first month of the lunar year. The lunar year begins on Chet Sudi: the first day after the new moon in Chet. This means that the first half of the purnimanta month of Chaitra goes to the previous year, while the second half belongs to the new Lunar year.The regional new year is observed on Vaisakhi which is determined by the solar calendar. The day is considered from sunrise to next sunrise and for the first day of the solar months, the Orissa rule is observed: day 1 of the month occurs on the day of the sankranti (known as sangrand in Punjabi).

Solar Hijri calendar

The Solar Hijri calendar (Persian: گاه‌شماری هجری خورشیدی‎, translit. gāh-shomāri-ye hejri-ye khorshidi; Pashto: لمريز لېږدیز کلیز‎), also called the Solar Hejri calendar or Shamsi Hijri calendar, and abbreviated as SH, is the official calendar of Iran and Afghanistan. It begins on the March equinox (Nowruz) as determined by astronomical calculation for the Iran Standard Time meridian (52.5°E, UTC+03:30) and has years of 365 or 366 days.

Its determination of the start of each year is astronomically accurate year-to-year as opposed to the more fixed Gregorian calendar or "Common Era calendar" which, averaged out, has the same year length, achieving the same accuracy (a more simply patterned calendar of 365 days for three consecutive years plus an extra day in the next year, save for exceptions to the latter in three out of every four centuries). The start of the year and its number of days remain fixed to one of the two equinoxes, the astronomically important days which have the same duration of day as night. It results in less variability of all celestial bodies when comparing a specific calendar date from one year to others.Each of the twelve months corresponds with a zodiac sign. The first six months have 31 days, the next five have 30 days, and the last month has 29 days in usual years but 30 days in leap years. The New Year's Day always falls on the March equinox.

Swedish calendar

The Swedish calendar (Swedish: Svenska kalendern) or Swedish style (Swedish: Svenska stilen) was a calendar in use in Sweden and its possessions from 1 March 1700 until 30 February 1712 (see below). It was one day ahead of the Julian calendar and ten days behind the Gregorian calendar. Easter was calculated nominally astronomically from 1740 to 1844.

Tamil calendar

The Tamil calendar is a sidereal Hindu calendar used by the Tamil people of the Indian subcontinent. It is also used in Puducherry, and by the Tamil population in Malaysia, Singapore, Mauritius and Sri Lanka. Tamil Nadu farmers greatly refer to this. It is used today for cultural, religious and agricultural events, with the Gregorian calendar largely used for official purposes both within and outside India. The Tamil calendar is based on the classical Hindu solar calendar also used in Assam, West Bengal, Kerala, Manipur, Nepal, Odisha, Rajasthan and Punjab.

There are several festivals based on the Tamil calendar. The Tamil New Year follows the nirayanam vernal equinox and generally falls on 14 April of the Gregorian year. 14 April marks the first day of the traditional Tamil calendar and this remains a public holiday in Tamil Nadu,and Sri Lanka. Tropical vernal equinox fall around 22 March, and adding 23 degrees of trepidation or oscillation to it, we get the Hindu sidereal or Nirayana Mesha Sankranti (Sun's transition into nirayana Aries). Hence, the Tamil calendar begins on the same date in April which is observed by most traditional calendars of the rest of India - Assam, Bengal, Kerala, Odisha, Manipur, Punjab etc. This also coincides with the traditional new year in Burma, Cambodia, Laos, Sri Lanka, Bangladesh Nepal and Thailand. The 60-year cycle is also very ancient and is observed by most traditional calendars of India and China, and is related to 5 revolutions of Jupiter according to popular belief, or to 60-year orbit of Nakshatras (stars) as mentioned in Surya Siddhanta.

The traditional Tamil year starts on 14 April 2019, Kaliyuga 5121. Vikrama and Shalivahana Saka eras are also used. There are several references in early Tamil literature to the April new year. Nakkirar, Sangam period author of the Neṭunalvāṭai, wrote in the third century CE that the sun travels each year from Mesha/Chitterai in mid-April through 11 successive signs of the zodiac. Kūdalūr Kizhaar in the third century CE refers to Mesha Raasi/Chitterai i.e. mid-April as the commencement of the year in the Puṟanāṉūṟu. The Tolkaapiyam is the oldest surviving Tamil grammar that divides the year into six seasons where Chitterai i.e. mid-April marks the start of the Ilavenil season or summer. The 8th century Silappadikaaram mentions the 12 Raasis or zodiac signs that correspond to the Tamil months starting with Mesha/Chitterai in mid-April. The Manimekalai alludes to this very same Hindu solar calendar as we know it today Adiyarkunalaar, an early medieval commentator or Urai-asiriyar mentions the twelve months of the Tamil calendar with particular reference to Chitterai i.e. mid-April. There were subsequent inscriptional references in Pagan, Burma dated to the 11th century CE and in Sukhothai, Thailand dated to the 14th century CE to South Indian, often Vaishnavite, courtiers who were tasked with defining the traditional calendar that began in mid-April.

Thai calendar

In Thailand, two main calendar systems are used alongside each other: the Thai solar calendar, based on the Gregorian calendar, used for official and most day-to-day purposes, and the Thai lunar calendar (a version of the Buddhist calendar, technically a lunisolar calendar), used for traditional events and Buddhist religious practices.

The use of the solar calendar was introduced in 1889 by King Chulalongkorn (Rama V), replacing the lunar calendar in official contexts. Originally placing the beginning of year on 1 April, this was changed to 1 January in 1941, so the days and months now correspond exactly to the Gregorian calendar. Numbering of the years follow the Buddhist Era, introduced in 1913 to replace the Rattanakosin Era, which in turn replaced the Chula Sakarat in 1889. The reckoning of the Buddhist Era in Thailand is 543 years ahead of the Common Era (Anno Domini), so the year 2019 CE corresponds to B.E. 2562.

The lunar calendar contains twelve or thirteen months in a year, with 15 waxing moon and 14 or 15 waning moon days in a month, amounting to years of 354, 355 or 384 days. The years are usually noted by the animal of the Chinese zodiac, although there are several dates used to count the New Year.

As with the rest of the world, the seven-day week is used alongside both calendars. The solar calendar now governs most aspects of life in Thailand, and while official state documents invariably follow the Buddhist Era, the Common Era is also used by the private sector. The lunar calendar determines the dates of Buddhist holidays, traditional festivals and astrological practices, and the lunar date is still recorded on birth certificates and printed in most daily newspapers.

Thai solar calendar

The Thai solar calendar (Thai: ปฏิทินสุริยคติ, RTGS: patithin suriyakhati, "solar calendar") was adopted by King Chulalongkorn (Rama V) in 1888 CE as the Siamese version of the Gregorian calendar, replacing the Thai lunar calendar as the legal calendar in Thailand (though the latter is still also used, especially for traditional and religious events). Years are now counted in the Buddhist Era (B.E.): พุทธศักราช, พ.ศ., (RTGS: Phutthasakkarat) which is 543 years ahead of the Gregorian calendar.

Tibetan festivals

In Tibet, the Tibetan calendar lags approximately four to six weeks behind the solar calendar. For example, the Tibetan First Month usually falls in February, the Fifth Month usually falls in June or early July and the Eight Month usually falls in September.

Tranquility Calendar

The Tranquility Calendar is a solar calendar proposal for calendar reform proposed by Jeff Siggins in 1989. It is a derivative of the International Fixed Calendar as well as the earlier Positivist Calendar published in 1849 by French philosopher Auguste Comte (1798–1857), providing for a year of 13 months of 28 days each, with one day at the end of each year belonging to no month or week, and a leap day approximately every 4 years.

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