Instruct: Given a question, retrieve relevant passages that answer the question.
Query: How many types of calendars are there?
Calendars fall into four types, lunisolar, solar, lunar, seasonal, besides calendars with "years" of fixed length, with no intercalation. Most pre-modern calendars are lunisolar. The seasonal calendars rely on changes in the environment rather than lunar or solar observations. The Islamic and some Buddhist calendars are lunar, while most modern calendars are solar, based on either the Julian or the Gregorian calendars.
A new version of Calendar with a text-heavy was added to Windows 8 as one of many apps written to run full-screen or snapped as part of Microsoft's Metro design language philosophy. It is one of three apps on Windows that originate from Microsoft Outlook, the other two being Mail and People apps. Structurally, the three apps are one and are installed and uninstalled as such. But each has its own user interface. Calendar in Windows 8 originally supported Outlook.com, Exchange, Google Calendar, and Facebook calendars. Because of API changes, Facebook and Google calendars can no longer be directly synced on Windows 8. Like many Microsoft apps introduced for Windows 8, many of the features are hidden in the charms or a menu at the bottom of the screen that is triggered by right clicking. Different calendars can be labeled with different colors. When a user with a Microsoft account adds a calendar account on one computer with Windows 8 Calendar, the account will be automatically added to all other Windows 8 computers the user is logged into. .ics files are not supported in this version.
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 Hijra (corresponding to AD 622)
With an annual drift of 11 or 12 days, the seasonal relation is repeated approximately each 33 Islamic years.
The basic element to the calendar is Sunday, which is a festival of Jesus’ resurrection. However, Christian Churches have historically observed other festivals which commemorate events in the life of Jesus or of significant individuals in the history of the Church. The purpose of the liturgical calendar is to guide commemorations as a part of the daily worship of the Lutheran Church. There is some variation associated with the observance of the calendar, as each Lutheran Church creates its own calendar and each congregation must choose independently how many individuals will be commemorated within a given year and how many festivals and lesser festivals they will publicly celebrate, especially if they do not coincide with a Sunday.
The calendar used by the Punjabi people varies by religions. Historically, the Punjabi Sikhs and Hindus have used the Indian Bikrami (Vikrami) calendar which started in 57 B.C. with King 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 2007, the Islamic Society of North America, the "Fiqh" Council of North America and the European Council for "Fatwa" and Research announced that they will henceforth use a calendar based on calculations using the same parameters as the "Umm al-Qura" calendar to determine (well in advance) the beginning of all lunar months (and therefore the days associated with all religious observances). This was intended as a first step on the way to unify, at some future time, Muslims' calendars throughout the world.
A leap year starting on Monday is any year with 366 days (i.e. it includes 29 February) that begins on Monday, 1 January, and ends on Tuesday, 31 December. Its dominical letters hence are GF, such as the years 1912, 1940, 1968, 1996, 2024, 2052, 2080, and 2120 in the Gregorian calendar or, likewise, 2008, 2036, and 2064 in the obsolete Julian calendar. 
Any leap year that starts on Monday, Wednesday or Thursday has two Friday the 13ths. This leap year contains two Friday the 13ths in September and December. Common years starting on Tuesday share this characteristic.
Year zero does not exist in the anno Domini system usually used to number years in the Gregorian calendar and in its predecessor, the Julian calendar. In this system, the year is followed by . However, there is a year zero in astronomical year numbering (where it coincides with the Julian year ) and in ISO 8601:2004 (where it coincides with the Gregorian year ) as well as in all Buddhist and Hindu calendars.
Hinduism and Buddhism were the prominent religions of southeast Asia in the 1st millennium CE, prior to the Islamic conquest that started in the 14th century. The Hindus prevailed in Bali, Indonesia and they have two types of Hindu calendar. One is a 210-day based Pawukon calendar which likely is a pre-Hindu system, and another is similar to lunisolar calendar system found in South India and it is called the Balinese saka calendar which uses Hindu methodology. The names of month and festivals of Balinese Hindus for the most part are different, though the significance and legends have some overlap.
A common year starting on Tuesday is any non-leap year (i.e. a year with 365 days) that begins on Tuesday, 1 January, and ends on Tuesday, 31 December. Its dominical letter hence is F. The current year, 2019, is a common year starting on Tuesday in the Gregorian calendar. The last such year was 2013 and the next such year will be 2030, or, likewise, 2014 and 2025 in the obsolete Julian calendar, see below for more. Any common year that starts on Sunday, Monday or Tuesday has two Friday the 13ths. This common year contains two Friday the 13ths in September and December. Leap years starting on Monday share this characteristic. From July of the year that precedes this year until September in this type of year is the longest period (14 months) that occurs without a Friday the 13th. Leap years starting on Saturday share this characteristic, from August of the common year that precedes it to October in that type of year.
For central Arabia, especially Mecca, there is a lack of epigraphical evidence but details are found in the writings of Muslim authors of the Abbasid era. Inscriptions of the ancient South Arabian calendars reveal the use of a number of local calendars. At least some of these South Arabian calendars followed the lunisolar system. Both al-Biruni and al-Mas'udi suggest that the ancient Arabs used the same month names as the Muslims, though they also record other month names used by the pre-Islamic Arabs.
In print, Arabic numerals are employed in Modern Hebrew for most purposes. Hebrew numerals are used nowadays primarily for writing the days and years of the Hebrew calendar; for references to traditional Jewish texts (particularly for Biblical chapter and verse and for Talmudic folios); for bulleted or numbered lists (similar to "A", "B", "C", "etc.", in English); and in numerology (gematria).
Historians have never included a year zero. This means that between, for example, and , there are 999 years: 500 years BC, and 499 years AD preceding 500. In common usage "anno Domini" 1 is preceded by the year 1 BC, without an intervening year zero. Neither the choice of calendar system (whether Julian or Gregorian) nor the era ("Anno Domini" or Common Era) determines whether a year zero will be used. If writers do not use the convention of their group (historians or astronomers), they must explicitly state whether they include a year 0 in their count of years, otherwise their historical dates will be misunderstood.
A leap year starting on Friday is any year with 366 days (i.e. it includes 29 February) that begins on Friday 1 January and ends on Saturday 31 December. Its dominical letters hence are CB, such as the years 1904, 1932, 1960, 1988, 2016, 2044, 2072, and 2112 in the Gregorian calendar or, likewise, 2000 and 2028 in the obsolete Julian calendar. Any leap year that starts on Tuesday, Friday or Saturday has only one Friday the 13th; The only Friday the 13th in this leap year occurs in May. Common years starting on Saturday share this characteristic.
ISO 8601:2004 (and previously ISO 8601:2000, but not ISO 8601:1988) explicitly uses astronomical year numbering in its date reference systems. Because it also specifies the use of the proleptic Gregorian calendar for all years before 1582, some readers incorrectly assume that a year zero is also included in that proleptic calendar, but it is not used with the BC/AD era. The "basic" format for year 0 is the four-digit form 0000, which equals the historical year 1 BC. Several "expanded" formats are possible: −0000 and +0000, as well as five- and six-digit versions. Earlier years are also negative four-, five- or six-digit years, which have an absolute value one less than the equivalent BC year, hence -0001 = 2 BC. Because only ISO 646 (7-bit ASCII) characters are allowed by ISO 8601, the minus sign is represented by a hyphen-minus.
A common year starting on Thursday is any non-leap year (i.e. a year with 365 days) that begins on Thursday, 1 January, and ends on Thursday, 31 December. Its dominical letter hence is D. The most recent year of such kind was 2015 and the next one will be 2026 in the Gregorian calendar or, likewise, 2010 and 2021 in the obsolete Julian calendar, see below for more. This common year contains the most Friday the 13ths; specifically, the months of February, March, and November. Leap years starting on Sunday share this characteristic.
From February until March in this type of year is also the shortest period (one month) that occurs within a Friday the 13th.
A leap year starting on Wednesday is any year with 366 days (i.e. it includes 29 February) that begins on Wednesday, 1 January, and ends on Thursday, 31 December. Its dominical letters hence are ED, such as the years 1908, 1936, 1964, 1992, 2020, 2048, 2076, and 2116 in the Gregorian calendar or, likewise, 2004 and 2032 in the obsolete Julian calendar.
Any leap year that starts on Monday, Wednesday or Thursday has two Friday the 13ths. This leap year contains two Friday the 13ths in March and November. Common years starting on Thursday share this characteristic, but also have another in February.
There are eight public holidays in Russia. The New Year is the first in calendar and in popularity. Russian New Year traditions resemble those of the Western Christmas, with New Year Trees and gifts, and Ded Moroz (Father Frost) playing the same role as Santa Claus. Rozhdestvo (Orthodox Christmas) falls on 7 January, because Russian Orthodox Church still follows the Julian (old style) calendar and all Orthodox holidays are 13 days after Catholic ones. Another two major Christian holidays are Paskha (Easter) and Troitsa (Trinity), but there is no need to recognize them as public holidays since they are always celebrated on Sunday.
There are three main types of tag cloud applications in social software, distinguished by their meaning rather than appearance. In the first type, there is a tag for the frequency of each item, whereas in the second type, there are global tag clouds where the frequencies are aggregated over all items and users. In the third type, the cloud contains categories, with size indicating number of subcategories.
The Julian year, as used in astronomy and other sciences, is a time unit defined as exactly 365.25 days. This is the normal meaning of the unit "year" (symbol "a" from the Latin "annus") used in various scientific contexts. The Julian century of days and the Julian millennium of days are used in astronomical calculations. Fundamentally, expressing a time interval in Julian years is a way to precisely specify how many days (not how many "real" years), for long time intervals where stating the number of days would be unwieldy and unintuitive. By convention, the Julian year is used in the computation of the distance covered by a light-year.
The smallest meaningful increment of time is the Planck time, the time light takes to traverse the Planck distance, many decimal orders of magnitude smaller than a second. The largest "realized" amount of time, given known scientific data, is the age of the universe, about 13.8 billion years - the time since the Big Bang as measured in the cosmic microwave background rest frame. Those amounts of time together span 60 decimal orders of magnitude. Metric prefixes are defined spanning 10 to 10, 48 decimal orders of magnitude which may be used in conjunction with the metric base unit of second. Metric units of time larger than the second are most commonly seen only in a few scientific contexts such as observational astronomy and materials science although this depends on author; for everyday usage and most other scientific contexts the common units of minutes (60 s), hours (3600 s or 3.6 ks), days (86 400 s), weeks, months, and years (of which there are a number of variations) are commonly used. Weeks, months and years are significantly variable units whose length crucially depends on the choice of calendar and is often not regular even with a calendar, e.g. leap years versus regular years in the Gregorian calendar. This makes them problematic for use against a linear and regular time scale such as that defined by the SI since it is not clear as to which version of these units we are to be using. Because of this, in the table below we will not use weeks and months and the year we will use is the Julian year of astronomy, or 365.25 days of 86 400 s exactly, also called an annum and denoted with the symbol "a", whose definition is based on the average length of a year of the Julian calendar which had one leap year every and always every 4 years against common years of 365 days each. This unit is used, following the convention of geological science, to form larger units of time by the application of SI prefixes to it at least up to "giga-annum", or Ga, equal to 1 000 000 000 a (short scale: one "billion" years, long scale: one "milliard" years).
There are many types of calendar, serving a wide variety of uses.
Google Calendar allows users to create and edit events. Events have a set start time and stop time, with an option for an "All-day event". Users can enable a "Recurring" functionality with optional parameters for frequency. Users can add a color to an event for recognition or to distinguish the event from others. Users can optionally set notifications, with options for type (email, mobile push notification) and time. Locations can be added for easy understanding of an event's place. Events are viewable in different types of setups, including day, week, month, or schedule. Users can invite other people to events; for other Google Calendar users, the event becomes visible in their calendar, and for non-Google Calendar users, an email will have options for "Yes", "No", or "Maybe". Privacy settings allow the user to define the levels of public visibility of the entire calendar or individual events. Although the calendar defaults to showing users event times in their local time, users can specify a different time zone for an event. Users can enable or disable the visibility of special calendars, including a Birthdays calendar, that automatically retrieves dates of births from a user's Google contacts and displays the dates on a yearly basis, and a Holidays calendar, a country-specific calendar featuring dates of special occasions.
Aztec religious life was organized around the calendars. As most Mesoamerican people, the Aztecs used two calendars simultaneously: a ritual calendar of 260 days called the "tonalpohualli" and a solar calendar of 365 days called the "xiuhpohualli". Each day had a name and number in both calendars, and the combination of two dates were unique within a period of 52 years. The tonalpohualli was mostly used for divinatory purposes and it consisted of 20 day signs and number coefficients of 1–13 that cycled in a fixed order. The "xiuhpohualli" was made up of 18 “months” of 20 days, and with a remainder of 5 “void” days at the end of a cycle before the new "xiuhpohualli" cycle began. Each 20-day month was named after the specific ritual festival that began the month, many of which contained a relation to the agricultural cycle. Whether, and how, the Aztec calendar corrected for leap year is a matter of discussion among specialists. The monthly rituals involved the entire population as rituals were performed in each household, in the "calpolli" temples and in the main sacred precinct. Many festivals involved different forms of dancing, as well as the reenactment of mythical narratives by deity impersonators and the offering of sacrifice, in the form of food, animals and human victims.
Three types of calendars can be found in Africa: lunar, solar, and stellar. Most African calendars are a combination of the three. African calendars include the Akan calendar, Egyptian calendar, Berber calendar, Ethiopian calendar, Igbo calendar, Yoruba calendar, Shona calendar, Swahili calendar, Xhosa calendar, Borana calendar, and Luba calendar.