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A solar calendar is a
calendar A calendar is a system of organizing days. This is done by giving names to periods of time, typically days, weeks, months and years. A date is the designation of a single and specific day within such a system. A calendar is also a phy ...
whose dates indicate the
season A season is a division of the year based on changes in weather, ecology, and the number of daylight hours in a given region. On Earth, seasons are the result of the axial parallelism of Earth's tilted orbit around the Sun. In temperate and ...
or almost equivalently the apparent position of the Sun relative to the stars. The
Gregorian calendar The Gregorian calendar is the calendar used in most parts of the world. It was introduced in October 1582 by Pope Gregory XIII as a modification of, and replacement for, the Julian calendar. The principal change was to space leap years d ...
, widely accepted as a standard in the world, is an example of a solar calendar. The main other type of calendar is a
lunar calendar A lunar calendar is a calendar based on the monthly cycles of the Moon's phases ( synodic months, lunations), in contrast to solar calendars, whose annual cycles are based only directly on the solar year. The most commonly used calendar, t ...
, whose months correspond to cycles of Moon phases. The months of the Gregorian calendar do not correspond to cycles of the Moon phase. The Egyptians appear to have been the first to develop a solar calendar, using as a fixed point the annual sunrise reappearance of the Dog Star—
Sirius Sirius is the brightest star in the night sky. Its name is derived from the Greek word , or , meaning 'glowing' or 'scorching'. The star is designated α Canis Majoris, Latinized to Alpha Canis Majoris, and abbreviated Alpha CM ...
, or Sothis—in the eastern sky, which coincided with the annual flooding of the Nile River. They constructed a calendar of 365 days, consisting of 12 months of 30 days each, with 5 days added at the year’s end. The Egyptians’ failure to account for the extra fraction of a day, however, caused their calendar to drift gradually into error.


Examples

The oldest solar calendars include the
Julian calendar The Julian calendar, proposed by Roman consul Julius Caesar in 46 BC, was a reform of the Roman calendar. It took effect on , by edict. It was designed with the aid of Greek mathematicians and astronomers such as Sosigenes of Alexandri ...
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
season A season is a division of the year based on changes in weather, ecology, and the number of daylight hours in a given region. On Earth, seasons are the result of the axial parallelism of Earth's tilted orbit around the Sun. In temperate and ...
s, 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 A tropical year or solar year (or tropical period) is the time that the Sun takes to return to the same position in the sky of a celestial body of the Solar System such as the Earth, completing a full cycle of seasons; for example, the time ...
, usually either the mean tropical year or the vernal equinox year. The following are tropical solar calendars: *Ancient Armenian calendar *
Gregorian calendar The Gregorian calendar is the calendar used in most parts of the world. It was introduced in October 1582 by Pope Gregory XIII as a modification of, and replacement for, the Julian calendar. The principal change was to space leap years d ...
* Bengali calendar (National and official calendar in Bangladesh) *
Iranian calendar The Iranian calendars or Iranian chronology ( fa, گاه‌شماری ایرانی, ) are a succession of calendars invented or used for over two millennia in Iran, also known as Persia. One of the longest chronological records in human history ...
(Jalāli calendar) ** Tabarian calendar (Tabarian calendar) * Indian national calendar (Saka calendar) 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 leap year (also known as an intercalary year or bissextile year) is a calendar year that contains an additional day (or, in the case of a lunisolar calendar, a month) added to keep the calendar year synchronized with the astronomical year or ...
, a method called " intercalation", the inserted day being "intercalary". The
Iranian calendar The Iranian calendars or Iranian chronology ( fa, گاه‌شماری ایرانی, ) are a succession of calendars invented or used for over two millennia in Iran, also known as Persia. One of the longest chronological records in human history ...
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 Tehran (; fa, تهران ) is the largest city in Tehran Province and the capital of Iran. With a population of around 9 million in the city and around 16 million in the larger metropolitan area of Greater Tehran, Tehran is the most popul ...
"by means of astronomical computations from reliable sources".


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. Leaping from one lunation to another, but one Sidereal year is the period between two occurrences of the sun, as measured by the stars' solar calendar, which is derived from the Earth's orbit around the sun every 28 years. Indian calendars like the
Hindu calendar The Hindu calendar, Panchanga () or Panjika is one of various lunisolar calendars that are traditionally used in the Indian subcontinent and Southeast Asia, with further regional variations for social and Hindu religious purposes. They adopt ...
, 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 The Hijri calendar ( ar, ٱلتَّقْوِيم ٱلْهِجْرِيّ, translit=al-taqwīm al-hijrī), also known in English as the Muslim calendar and Islamic calendar, is a lunar calendar consisting of 12 lunar months in a year of 354 ...
, which is a purely
lunar calendar A lunar calendar is a calendar based on the monthly cycles of the Moon's phases ( synodic months, lunations), in contrast to solar calendars, whose annual cycles are based only directly on the solar year. The most commonly used calendar, t ...
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, therefore it is not a solar calendar. Also, any calendar synchronized only to the synodic period of Venus would not be solar.


Lunisolar calendars

Lunisolar calendar A lunisolar calendar is a calendar in many cultures, combining lunar calendars and solar calendars. The date of Lunisolar calendars therefore indicates both the Moon phase and the time of the solar year, that is the position of the Sun in ...
s are lunar calendars that have additional intercalation rules to roughly synchronize the solar year and the seasons. Typical lunisolar calendars have years marked with a whole number of lunar months, so they can not indicate the position of Earth relative to the Sun with the same accuracy as a purely solar calendar.


List of solar calendars

The following is a list of current, historical, and proposed solar calendars: *
Assamese calendar The Assamese Calendar ( as, ভাস্কৰাব্দ, , Bhāskarābda) is a luni-solar calendar, followed in the Indian state of Assam. The New Year in the Assamese calendar is known as ''Bohag Bihu''. The calendar is counted from the date ...
*
Assyrian calendar Assyrian may refer to: * Assyrian people, the indigenous ethnic group of Mesopotamia. * Assyria, a major Mesopotamian kingdom and empire. ** Early Assyrian Period ** Old Assyrian Period ** Middle Assyrian Empire ** Neo-Assyrian Empire * Assyrian ...
* Astronomical year numbering * Badí‘ calendar * Basotho calendar * Bengali calendar *
Berber calendar The Berber calendar ( ber, ⵜⴰⵙⵡⴰⵙⵜ ⵜⴰⵎⴰⵣⵉⵖⵜ, taswast tamaziɣt) is the agricultural calendar traditionally used by Berbers. It is also known as the rustic ( ar, ﻓﻼّﺣﻲ, fellaḥi) calendar. The calendar is u ...
*
Bulgar calendar The Bulgar calendar was a solar calendar system used by the Bulgars, a Turkic people, originally from Central Asia, who from the 4th century onwards dwelt in the Eurasian steppes north of the Caucasus and around the banks of river Volga. In 681, pa ...
*
Byzantine calendar The Byzantine calendar, also called the Roman calendar, the Creation Era of Constantinople or the Era of the World ( grc, Ἔτη Γενέσεως Κόσμου κατὰ Ῥωμαίους, also or , abbreviated as ε.Κ.; literal translation of ...
* Caesar's CalendarDenis Feeney. (2007). Caesar's Calendar : Ancient Time and the Beginnings of History. University of California Press * Coptic calendar * Discordian calendar * Era Fascista *
Ethiopian calendar The Ethiopian calendar ( am, የኢትዮጲያ ዘመን ኣቆጣጠር; Oromo: Akka Lakkofsa Itoophiyaatti; Ge'ez: ዓዉደ ወርሕ; Tigrinya: ዓዉደ ኣዋርሕ), or Ge'ez calendar ( Ge'ez: ዓዉደ ወርሕ; Tigrinya: ዓ� ...
* Florentine calendar * French Republican Calendar *
Gregorian calendar The Gregorian calendar is the calendar used in most parts of the world. It was introduced in October 1582 by Pope Gregory XIII as a modification of, and replacement for, the Julian calendar. The principal change was to space leap years d ...
* Hanke-Henry Permanent Calendar *
Holocene calendar The Holocene calendar, also known as the Holocene Era or Human Era (HE), is a year numbering system that adds exactly 10,000 years to the currently dominant ( AD/ BC or CE/ BCE) numbering scheme, placing its first year near the beginning of th ...
* Indian national calendar *
International Fixed Calendar The International Fixed Calendar (also known as the IFC, Cotsworth plan, the Cotsworth calendar and the Eastman plan) is a proposed calendar reform designed by Moses B. Cotsworth, first presented in 1902. The solar calendar divides the year into ...
*
Invariable Calendar In April 1900, Professor L. A. Grosclaude of Geneva proposed the Invariable Calendar, New Era Calendar, or Normal Calendar with 12 months and four 91-day quarters of exactly 13 weeks. An additional day, termed New Year's Day, that was not any day of ...
*
Jalali calendar The Jalali calendar is a solar calendar, was compiled during the reign of Jalaluddin Malik-Shah I of Seljuk by the order of Nizam al-Mulk and the place of observation were the cities of Isfahan (the capital of the Seljuks), Rey, and Nishapur. ...
*
Javanese calendar The Javanese calendar ( jv, ꦥꦤꦁꦒꦭ꧀ꦭꦤ꧀ꦗꦮ, Pananggalan Jawa) is the calendar of the Javanese people. It is used concurrently with two other calendars, the Gregorian calendar and the Islamic calendar. The Gregorian calendar ...
* Juche era calendar *
Julian calendar The Julian calendar, proposed by Roman consul Julius Caesar in 46 BC, was a reform of the Roman calendar. It took effect on , by edict. It was designed with the aid of Greek mathematicians and astronomers such as Sosigenes of Alexandri ...
* Malayalam calendar * Minguo calendar * Nanakshahi calendar * Odia calendar * Old Icelandic calendar * Pancronometer * Pataphysical calendar *
Pax Calendar The Pax calendar was invented by James A. Colligan, SJ in 1930 as a perennializing reform of the annualized Gregorian calendar. Design The common year is divided into 13 months of 28 days each, whose names are the same as in the Gregorian cal ...
* Pentecontad calendar * Pisan calendar *
Positivist calendar The positivist calendar was a calendar reform proposal by Auguste Comte (1798–1857) in 1849. Revising the earlier work of Marco Mastrofini, or an even earlier proposal by "Hirossa Ap-Iccim" ( Hugh Jones), Comte developed a solar calendar with 13 ...
* Revised Julian calendar *
Roman calendar The Roman calendar was the calendar used by the Roman Kingdom and Roman Republic. The term often includes the Julian calendar established by the reforms of the dictator Julius Caesar and emperor Augustus in the late 1stcenturyBC and some ...
* Runic calendar * Solar Hijri calendar * Soviet calendar * Swedish calendar * Symmetry454 * Tamil calendar * Thai solar calendar * Tulu calendar * World Calendar * World Season Calendar


See also

*
List of calendars This is a list of calendars. Included are historical calendars as well as proposed ones. Historical calendars are often grouped into larger categories by cultural sphere or historical period; thus O'Neil (1976) distinguishes the groupings Egyptian ...
* Analemma calendar * Astronomical clock * Daytime (astronomy)


References


External links

*
Correspondence between Hebrew and Islamic calendars, months and holidays (pdf)
{{DEFAULTSORT:Solar calendar