Editing Solar calendar

{{Short description|Calendar based on the seasons or apparent sun position}}
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A '''solar calendar''' is a [[calendar]] whose dates indicates the [[season]] or almost equivalently the apparent [[position of the Sun]] relative to the stars. The [[Gregorian calendar]], widely accepted as a standard in the world, is an example of a solar calendar.
The main other types of calendar are [[lunar calendar]] and [[lunisolar calendar]], whose months correspond to cycles of [[Moon phase]]s. 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]], 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]] 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===
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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]]s, that is, they are synchronized with the [[declination]] of the Sun. Such a calendar is called a '''tropical solar calendar''' {{cn|date=November 2017}}..

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:
*Ancient Armenian calendar
*[[Bengali calendar]] (National and official calendar in Bangladesh)
*[[Gregorian calendar]]
*[[Iranian calendar]] (Jalāli calendar)
**[[Tabarian calendar]] (Tabarian calendar)
*[[Indian national calendar]] (Saka calendar)
*[[French Republican 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 method called "[[Intercalation (timekeeping)|intercalation]]", the inserted day being "intercalary".

The [[Baháʼí calendar]], another example of a solar calendar, always begins the year on the [[March equinox|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 using the location of [[Tehran]] "by means of astronomical computations from reliable sources".<ref name="UHJ1">{{cite web | title = To the Bahá'ís of the World | last = The Universal House of Justice | url = http://universalhouseofjustice.bahai.org/activities-bahai-community/20140710_001 | date = 2014-07-10 | access-date = 2014-07-10}}</ref>

===Sidereal solar calendars===
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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'''.<ref>Helen R. Jacobus. (2014). Zodiac Calendars in the Dead Sea Scrolls and Their Reception : Ancient Astronomy and Astrology in Early Judaism. Brill
</ref>

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.<ref>Leofranc Holford-Strevens. (2005). The History of Time: A Very Short Introduction. OUP Oxford</ref>

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

==Non-solar calendars==
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The [[Islamic calendar]] 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, therefore it is not a solar calendar.
Also, any calendar synchronized only to the [[synodic period]] of [[Venus]] would not be solar.

==Lunisolar calendars==
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[[Lunisolar calendar]]s may be regarded as solar calendars, although their dates additionally indicate the moon phase. 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:

{{div col|colwidth=20em}}
* [[Assamese calendar]]
* [[Assyrian calendar]]
* [[Badí‘ calendar]] 
* [[Basotho calendar]]
* [[Bengali calendars|Bengali calendar]]
* [[Berber calendar]] 
* [[Bulgar calendar]]
* [[Byzantine calendar]]
* [[Caesar's Calendar]]<ref>Denis Feeney. (2007). Caesar's Calendar : Ancient Time and the Beginnings of History. University of California Press</ref>
* [[Coptic calendar]]
* [[Discordian calendar]] 
* [[EartHeaven calendar]]<ref>Steve Howland. (2024). The EartHeaven Calendar : A white paper presenting a fixed calendar solution for the next 2100 years of this Aquarian Age. Ampers& Studio, Publisher. https://ehc.world</ref> 
* [[Era Fascista]] 
* [[Ethiopian calendar]] 
* [[Florentine calendar]] 
* [[French Republican Calendar]]
* [[Gregorian calendar]] 
* [[Hanke–Henry Permanent Calendar|Hanke-Henry Permanent Calendar]] 
* [[Holocene calendar]]
* [[Indian national calendar]]
* [[International Fixed Calendar]] 
* [[Invariable Calendar]]  
* [[Jalali calendar]]
* [[North Korean calendar|Juche calendar]]
* [[Julian calendar]]
* [[Maithili calendar]]
* [[Malayalam calendar]] 
* [[Minguo calendar]] 
* [[Nanakshahi calendar]]
* [[Odia calendar]]
* [[Germanic calendar|Old Icelandic calendar]] 
* [[Hugh Jones (professor)#Georgian Calendar (Pancronometer)|Pancronometer]]
* [[Pataphysical calendar]]
* [[Pax Calendar]] 
* [[Pentecontad calendar]]
* [[Pisan calendar]] 
* [[Positivist calendar]]
* [[Revised Julian calendar]] 
* [[Roman calendar]] {{Citation needed|reason=Probably it is an [[Lunisolar calendar]], [[Common year]]s: 355 days, [[Leap year]]s: 378 days! |date=March 2020}}
* [[Runic calendar]] 
* [[Shaka Samvat]]
* [[Solar Hijri calendar]]
* [[Soviet calendar]]
* [[Swedish calendar]] 
* [[Symmetry454]] 
* [[Tamil calendar]] 
* [[Thai solar calendar]] 
* [[Tulu calendar]] 
* [[World Calendar]] 
* [[World Season Calendar]]
* [[Yoruba calendar]]
* [[Zoroastrian calendar]]
{{div col end}}

==See also==
*[[List of calendars]]
*[[Analemma calendar]]
*[[Astronomical clock]]
*[[Daytime (astronomy)]]

==References==
{{Reflist}}

==External links==
*{{Commonscatinline|Solar calendars}}
*[http://www.alsadiqin.org/history/The%20Islamic%20Jewish%20Calendar.pdf Correspondence between Hebrew and Islamic calendars, months and holidays (pdf)]

{{Calendars}}
{{Time measurement and standards}}
{{Chronology}}

{{DEFAULTSORT:Solar calendar}}
[[Category:Solar calendars| ]]