Calendar

===Religious===
[[File:Hindu calendar 1871-72.jpg|thumb|A Hindu [[almanac]] (''pancanga'') for the year 1871/2 from [[Rajasthan]] (Library of Congress, Asian Division)]]
The most important use of pre-modern calendars is keeping track of the [[liturgical year]] and the observation of religious feast days.

While the Gregorian calendar is itself historically motivated to the calculation of the [[Easter date]], it is now in worldwide secular use as the ''de facto'' standard. Alongside the use of the Gregorian calendar for secular matters, there remain several calendars in use for religious purposes.

Western Christian liturgical calendars are based on the cycle of the Roman Rite of the Catholic Church and generally include the liturgical seasons of [[Advent]], [[Christmas]], Ordinary Time (Time after [[Epiphany (holiday)|Epiphany]]), [[Lent]], [[Easter]], and Ordinary Time (Time after [[Pentecost]]). Some Christian calendars do not include Ordinary Time and every day falls into a denominated season.

[[Eastern Christians]], including the [[Eastern Orthodox Church|Orthodox Church]], use the [[Julian calendar]].

The [[Islamic calendar]] or Hijri calendar is a [[lunar calendar]] consisting of 12 lunar months in a year of 354 or 355 days. It is used to date events in most of the Muslim countries (concurrently with the Gregorian calendar) and used by Muslims everywhere to determine the proper day on which to celebrate Islamic holy days and festivals. Its epoch is the [[Anno Hegirae|Hijra]] (corresponding to AD&nbsp;622). With an annual drift of 11 or 12 days, the seasonal relation is repeated approximately every 33 Islamic years.

Various [[Hindu calendar]]s remain in use in the Indian subcontinent, including the [[Nepali calendar (disambiguation)|Nepali calendars]], [[Bengali calendar]], [[Malayalam calendar]], [[Tamil calendar]], [[Vikrama Samvat]] used in Northern India, and [[Shalivahana era|Shalivahana]] calendar in the [[Deccan Plateau|Deccan]] states.

The [[Buddhist calendar]] and the traditional lunisolar calendars of [[Cambodia]], [[Laos]], [[Myanmar]], [[Sri Lanka]] and [[Thailand]] are also based on an older version of the Hindu calendar.

Most of the Hindu calendars are inherited from a system first enunciated in [[Vedanga Jyotisha]] of Lagadha, standardized in the ''[[Surya Siddhanta|Sūrya Siddhānta]]'' and subsequently reformed by astronomers such as [[Aryabhata|Āryabhaṭa]] (AD&nbsp;499), [[Varahamihira|Varāhamihira]] (6th century) and [[Bhāskara II]] (12th century).

The [[Hebrew calendar]] is used by [[Jews]] worldwide for religious and cultural affairs, also influences civil matters in Israel (such as [[public holiday|national holidays]]) and can be used business dealings (such as for the dating of [[cheque]]s).<ref>{{Cite web |title=About the Hebrew Calendar {{!}} Yale University Library |url=https://web.library.yale.edu/cataloging/hebraica/about-hebrew-calendar |access-date=2024-03-18 |website=web.library.yale.edu}}</ref>

Followers of the [[Baháʼí Faith]] use the [[Baháʼí calendar]]. The Baháʼí Calendar, also known as the Badi Calendar was first established by the Bab in the Kitab-i-Asma. The Baháʼí Calendar is also purely a solar calendar and comprises 19 months each having nineteen days.