• The sample calendar is limited to the past three months.

Days of Religious Observance

Most Christians belong to the Western Christian churches, of which the Roman Catholic Church is the largest, both in the United States and in the world. Other Western Christian churches include the Protestant Churches and the Churches of the Anglican Communion. Denominations that belong to the Western Christian faith follow the Gregorian calendar, which was established by Pope Gregory XIII in 1582 and is remarkably accurate, differing from the solar year by only 26 seconds. Easter is the holiest day of observance for Christians. Its date determines the dates of all other major days of observance with the exception of Christmas, which is on the fixed date of December 25.

Easter falls on the first Sunday after the ecclesiastical full moon date following the ecclesiastical vernal equinox. The ecclesiastical full moon dates were predicted by astronomers in 325 A.C.E. at the First Council of Nicaea. Easter can fall as early as March 22 and as late as April 25.

Religious holidays and festivals vary in the timing of their observance. Jewish holidays start at sundown the day before the first full day of the holiday and end at sundown on the last day of the holiday.

Baha’i and Pagan/Wiccan holidays also begin at sunset the day preceding the holiday.

Islamic holidays are based on a lunar calendar and begin at sundown the day before the first full day of the holiday. Since the Muslim lunar year is about eleven days shorter than the solar year, Islamic holidays shift earlier every year with respect to the Gregorian calendar. Thus Islamic holidays move through different seasons over the years, and a holiday may occur twice in the same Gregorian year. The Islamic lunar calendar (the Umm al-Qura), used in Saudi Arabia and most of the Arabian Peninsula, relies on astronomical calculations with sunrises, sunsets, moon phases, moonrises, and moonsets based on the geographical location of Mecca to determine the start of each Islamic month. In countries outside the Arabian Peninsula, however, the start of each month is determined by direct observation with the naked eye of the moon’s first crescent (hilal) following the new moon. For example, the holy month of Ramadan begins at the sighting of the first lunar crescent following the new moon. If the first crescent is not visible due to atmospheric or other conditions, then the new month begins at sundown the following day. Islamic holidays that fall on the first day of an Islamic month, such as Al Hijrah (New Year) and Eid al-Fitr, also begin at sundown at the sighting of the first crescent. This is why Islamic months and holidays may begin a day later in countries outside the Arabian Peninsula. Moreover, because Muslims rely on different locations for the observation of the crescent moon, with some requiring reports of its sighting from within their national borders and others accepting reports from other locations such as Mecca or Jerusalem, different Muslim communities start months on different days. In this calendar we have used the dates for Islamic holidays based on the Umm al-Qura calendar used in Saudi Arabia and most of the Arabian Peninsula.

Followers of the two main sects of Islam differ in their observance of some Muslim holidays. While the beginning of Ramadan and the feasts of Eid al-Fitr (the end of Ramadan) and Eid al-Adha (the end of the Hajj) are equally important to both Sunni and Shi’a Muslims, the holiday of Ashura differs greatly in importance to the two sects. For Sunnis, Ashura is a minor holiday with a voluntary fast, while for Shi’a Muslims, Ashura is perhaps the defining holiday of their faith and the holiest day of the year. It commemorates the event that deepened the schism between the two sects—the martyrdom of Hussein ibn Ali, grandson of the Prophet Muhammad, in Karbala. For Shi’as, Ashura is a day of commemoration and pilgrimage to the shrine of Hussein at Karbala, as is the observance of Arbaeen, which marks the end of the 40-day mourning period following Ashura.

Coptic Orthodox Christian and Eastern Orthodox Christian holidays begin with the celebration of vespers at sundown the day before the first full day of the holiday, which is the beginning of the liturgical day. Coptic Orthodox Christians and most Eastern Orthodox Christians follow the Orthodox Old Calendar, or Julian calendar, in which fixed holidays currently fall thirteen days later than Western Christian holidays in the Gregorian calendar. For example, Christmas is celebrated on December 25 by Western Christians, while Orthodox Christians celebrate Christmas on January 7. Since the vernal equinox is used in calculating the date for Easter, the dates for Orthodox Easter and all related moveable holidays usually differ from those in the Western Christian Churches. Several Eastern Orthodox Churches, such as the Greek and Cypriot Orthodox Churches, follow the Orthodox New Calendar, in which the Gregorian calendar is used for fixed holidays such as Christmas, and the Julian calendar is used for calculating Easter and all related moveable feasts.

There are two different branches of Buddhism: Theravada, the only surviving school of the original sects of Buddhism and the predominant religion of continental Southeast Asia and Sri Lanka, also found in parts of Indonesia, Malaysia, and Vietnam; and Mahayana, the later revisionist school of Buddhism found primarily in China, Japan, and Korea, and parts of the Republic of China and Vietnam. Offshoots of the Mahayana tradition include Vajrayana, found in Tibet and Mongolia, Jodo (Pure Land), and Zen Buddhism. Buddhists who follow the Theravada tradition celebrate holidays according to the lunar calendar, in which dates of observance vary from year to year, while those who follow the Mahayana tradition celebrate holidays on fixed dates, based on the Japanese Buddhist calendar. In this calendar, Visakaha Day is observed in accordance with the Theravada school, while all other Buddhist holidays follow the Mahayana tradition.

Hinduism is one of the world’s oldest religions, having originated in what is now India in the second millennium B.C. It has an estimated 900 million followers worldwide, predominantly in India, Nepal, and Southeast Asia. Hinduism is a complex of polytheistic religion and philosophy that evolved from Vedism and seeks to help people move beyond human imperfection. The Hindu lunisolar calendar is based on a year of 12 lunar months, with the discrepancy between this lunar year and the solar year of 365 days resolved by adding an extra month every 30 months. Months can begin with a new moon and end with a new moon (amānta māna), as in southern India, or they can begin with a full moon and end with a full moon (pūrnimānta māna), as in northern India. The dates of Hindu holidays can vary by one day depending upon astronomical phenomena as well as on the location and time zone of the observer. The Hindu day begins at sunrise and ends at sunrise the following day. In contrast, the Hindu festival date, or tithi, is a lunar day based on the angle between the moon and the sun, and can begin at any time of day and vary in duration from approximately 19 to 26 hours. There are 15 tithis in each Paksha fortnight—15 tithis in the “bright fortnight” or waxing moon (Shukla Paksha) and 15 tithis in the “dark fortnight” or waning moon (Krishna Paksha)—for a total of 30 tithis in a lunar month. A day is designated with the number of the tithi in which the sunrise of that day occurs. Due to the varying duration of tithis, two successive days can have the same tithi, or a tithi may be omitted or “lost.” This interaction of lunar days with solar days creates a complex and unique calendar system.

The Sikh community has traditionally followed the Hindu Bikarami calendar, a lunar calendar in which the dates of Sikh holidays move from year to year. Since the Bikarami calendar does not Conform to the tropical year length, this continual shifting of dates has led to festivals being celebrated out of season. In order to remedy this discrepancy and also to give the Sikh community their own separate calendar, the Nanakshahi calendar was created, named after the founder of Sikhism, Guru Nanak. Introduced in 1999 and officially approved by the Sikh clergy in 2003, the Nanakshahi calendar converts all Gurupurabs, the festivals marking events in the lives of the Gurus, to fixed dates in the Gregorian solar calendar. All Sikh festivals are now celebrated on their Nanakshahi dates, with the exception of Hola Muhalla, Bandi Chhor Day, and Guru Nanak Ji’s Birthday, which are still celebrated according to the traditional Bikarami calendar. Effective as of the Sikh New Year on March 14, 2010, the Shiromani Gurdwara Prabandhak Committee (SGPC) Amritsar, elected by the Sikh Nation, has in the case of most Sikh dates reverted back to the Bikarami Hindu calendar, while the vast majority of the Sikh diaspora has rejected the SGPC decision and continues to follow the Nanakshahi calendar.

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