Dates and Calendars

Online Resources

• Genealogical Feast Day Calendars - Julian and Gregorian
  • Calendar Changes between the Julian and the Gregorian calendars
• Lutheran Liturgical Calendar
• Date Calculator
• Birth and Death Date Calculators
• Age calculator
• Tombstone birthday calculator
• Day of the week calculator
• Easter Sunday calculator

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• Germany Feast Day Calendars
• England Calendar Changes
• French Republican Calendar
• Western-Chinese Calendar Converter
• Conversion between Chinese and Western Calendar in Two Thousand Years - 兩千年中西曆轉換 - February 11, 1 AD to January 29, 2101
• Convert Chinese dates
• Latin date converter - For Iceland
• Calendar: Soviet

"A calendar is a system of organizing days. This is done by giving names to periods of time, typically days, weeks, months and years." Globally, there are six major calendars still in use:

• Gregorian Calendar
• Jewish Calendar
• Islamic Calendar
• Indian Calendar
• Chinese Calendar
• Julian Calendar

Gregorian Calendar

The Gregorian calendar is the accepted international standard calendar, and is used in almost every country for civil and administrative purposes. It is a solar calendar, meaning that it is based on the Earth's revolution around the Sun. The Gregorian calendar is updated regularly as needed by the IERS. The International Earth Rotation and Reference Systems Service (IERS) is responsible for making sure that the calendar stays in sync with the Earth's rotation.
The Gregorian calendar is used for both religious and secular purposes. It is the official calendar of the Catholic Church, and it is also used by most governments and businesses around the world. The calendar is also used to determine the dates of holidays and other important events.
The calendar was created in 1582 by Pope Gregory XIII and is named after him. It was implemented to correct errors in the Julian calendar, which was causing the date of Easter to drift out of sync with the spring equinox.
Key features of the Gregorian calendar:

• 12 months: The year is divided into 12 months, with 31 days in January, March, May, July, August, October, and December; 30 days in April, June, September, and November; and 28 days in February (except in leap years, which occur every four years and have 29 days in February).
  • The 12 months in order are: January, February, March, April, May, June, July, August, September, October, November, December.
• Leap years: Leap years are added to keep the calendar in sync with the Earth's orbit around the Sun. A leap year is (typically) any year that is divisible by 4 but not by 100, or any year that is divisible by 400.
• Weeks: The week is a seven-day period that is not based on any astronomical event. It is simply a convenient way to divide up the month.

History
The Gregorian calendar was developed by a team of astronomers and mathematicians led by Aloysius Lilius. The calendar was presented to Pope Gregory XIII in 1577, and he signed a papal bull, Inter gravissimas, in 1582, which officially adopted the calendar.
The calendar was initially met with resistance from some countries, particularly Protestant countries, who saw it as a symbol of Catholic authority. However, over time, the calendar was adopted by more and more countries, and it is now the most widely used calendar in the world.

For years that each country adopted the Gregorian calendar, see Julian and Gregorian Calendars.

Julian Calendar

The Julian calendar, introduced by Julius Caesar in 45 BC, marked a major advancement in timekeeping. This solar calendar, based on the Earth's revolution around the sun, replaced the previously used Roman calendar, which was inaccurate and inconsistent.
Key feature of the Julian calendar include:

• 365 days: The Julian calendar is a solar calendar, consisting of 365 days in a common year and 366 days in a leap year.
• 12 months: The year is divided into 12 months, with varying lengths ranging from 28 to 31 days.
  • Names of the 12 months in order are: Ianuarius, Februarius, Martius, Aprilis, Maius, Iunius, Quintilis, Sextilis, September, October, November, and December.
• Leap day: February gains an extra day in leap years, making it 29 days instead of 28.

History
Prior to the Julian calendar, the Roman calendar was based on lunar cycles and had only 355 days. This led to significant discrepancies with the solar year, resulting in seasonal misalignments and calendar adjustments being necessary every few years. Recognizing these inaccuracies, Julius Caesar, with the help of the astronomer Sosigenes of Alexandria, introduced the Julian calendar. This new system incorporated a leap year every four years, ensuring that the calendar year remained closely aligned with the solar year. The Julian calendar proved to be a major improvement, offering greater accuracy and predictability. It quickly gained widespread adoption throughout the Roman Empire and eventually much of the Western world. Despite its accuracy, the Julian calendar still had a slight discrepancy with the solar year. This discrepancy, amounting to about 11 minutes per year, accumulated over time, leading to a gradual shift in the calendar's alignment with the seasons.

Jewish Calendar

The Jewish calendar, also known as the Hebrew calendar, is a blend of lunar and solar cycles, with a history dating back thousands of years. It is used by Jewish communities worldwide for religious purposes and to determine the dates of festivals and holidays. The year 5784 on the Jewish calendar began on September 16, 2023.

• 12 months: The year consists of 12 months, with each month beginning and ending with a new moon.
  • The 12 months in order are: Nisan, Iyar, Sivan, Tammuz, Av, Elul, Tishrei, Heshvan, Kislev, Tevet, Shevat, and Adar.
• Intercalary month: (Adar II) The length of the year is determined by adding an intercalary month (Adar II) seven times every 19 years.

History
The origins of the Jewish calendar can be traced back to the ancient Israelites, who observed a lunar calendar based on the cycles of the moon. This calendar was used to determine the dates of religious festivals and observances, such as Rosh Hashanah and Yom Kippur. Over time, however, the lunar calendar became increasingly inaccurate, as it did not account for the Earth's revolution around the sun.
In the 4th century CE, Jewish leaders recognized the need for a more precise calendar. They developed a new calendar that was based on both the lunar and solar cycles. This new calendar, known as the Hillel II calendar, is the one that is still used by Jews today.

Islamic Calendar

The Islamic calendar, also known as the Hijri calendar, is a synodic lunar calendar based on the cycles of the moon. It is used by Muslims worldwide to determine the dates of religious holidays and observances, such as Ramadan, Eid al-Fitr, and Eid al-Adha. Unlike the Gregorian calendar, which is based on the Earth's orbit around the sun, the Islamic calendar is approximately 11 days shorter each year.
The year 1445 on the Islamic calendar began on July 19, 2023. The first month of the Islamic calendar, Muharram, is considered a sacred month and is a time for reflection and mourning. The Islamic calendar is used as the official calendar in several Muslim-majority countries.

• 12 months: The Islamic year consists of 12 lunar months, with each new month starting with the declaration of a new moon by religious authorities.
• Days: The months have 29 or 30 days, with no intercalary months.
• Year: The year is approximately 11 days shorter than the solar year, which means that Islamic holidays move forward by about 11 days each year relative to the Gregorian calendar.

The names of the Islamic months are:

Muharram Safar Rabi' al-Awwal Rabi' al-Thani Jumada al-Ula Jumada al-Thaniya Rajab Sha'ban Ramadan Shawwal Dhu al-Qi'dah Dhu al-Hijjah

History
The Islamic calendar began with the Hijra, the Prophet Muhammad's migration from Mecca to Medina in 622 CE. This event marked a turning point in Islamic history and is considered the start of the Islamic era. Prior to the Hijra, the Arabs used a lunar calendar with intercalary months added to keep it aligned with the solar year. However, this system was inaccurate and led to confusion. The Prophet Muhammad established the Islamic calendar to create a purely lunar calendar that was more precise and unified for Muslims.

Indian Calendar

India uses a complex and fascinating calendar system. Unlike the Gregorian calendar, a single, unified calendar hasn't prevailed throughout the Indian subcontinent. Instead, a collection of regional calendars based on lunar, solar, and lunisolar cycles have been used for centuries, each reflecting the unique cultural and astronomical practices of different regions.
The diverse Indian calendars are used for various purposes, including religious observances:

• Religious observances: Determining the dates of festivals, holidays, and auspicious days for rituals and ceremonies.
• Agricultural practices: Planning based on seasonal cycles and weather patterns.
• Social events: Scheduling weddings, birthdays, and other social gatherings.
• Historical dating: Understanding the chronological framework of ancient Indian history.

The Indian subcontinent boasts a diverse range of calendars, each with its own unique characteristics and origins. There are many unique indigenous calendars used by various tribal communities across India.
Some of the most prominent calendars include:

• Hindu calendars: These lunisolar calendars are based on both the lunar and solar cycles. There are several regional variations, such as the Shalivahana Shaka (used in South India), the Vikram Samvat (North and Central India), and the Kollam Era (Kerala).
  • The Hindu calendar year is divided into six seasons, each with its own distinct characteristics and associated festivals.
• Buddhist calendars: These calendars are based on the lunar cycle and are used by Buddhist communities across India.
• Jain calendars: These calendars are also based on the lunar cycle and are used by Jain communities.
  • The Jain calendar has a unique cycle of 57 years, known as the "Kalpa." The Kalpa cycle is used for dating historical events as well as for astrological calculations and religious observances.
• Indian national calendar: The Indian national calendar, adopted in 1957, is a solar calendar based on the Shalivahana Shaka era. It is used for official purposes throughout India.
  • The Indian national calendar is unique in that it starts its year on the same day as the Gregorian calendar (January 1st) but has different month names and lengths.

History
The earliest evidence of timekeeping in India dates back to the Indus Valley Civilization (3300-1300 BCE), where archaeologists have discovered seals and artifacts with markings suggestive of lunar cycles and calendar systems. The Vedic texts, composed around 1500-500 BCE, also mention various units of time, including days, months, and years, based on astronomical observations. These early calendars were primarily lunar, reflecting the importance of the moon in Hindu mythology and rituals.

Chinese Calendar

The Chinese calendar, also known as the Lunisolar calendar, is a system that has been used in China for centuries. It is based on the cycles of the moon and the sun, creating a unique calendar that differs significantly from the Gregorian calendar used in most parts of the world. The Chinese calendar is used to determine the dates of all major holidays and festivals, including Chinese New Year, Lantern Festival, and Dragon Boat Festival. It also plays a role in traditional Chinese medicine, astrology, and other cultural practices. The Chinese calendar remains an important part of Chinese identity and heritage, and many people continue to use it alongside the Gregorian calendar in daily life.
The year 4720 on the Chinese calendar began on February 5, 2023. This pertains to the sexagenary cycle, which combines the 10 Heavenly Stems and 12 Earthly Branches. This cycle repeats every 60 years.

Key features of the Chinese calendar include:

• 12 months: The year consists of 12 lunar months, each with 29 or 30 days.
  • The modern names of the lunar months are: 正月; zhēngyuè; 'first month', 二月; èryuè; 'second month', 三月; sānyuè; 'third month', 四月; sìyuè; 'fourth month', 五月; wǔyuè; 'fifth month', 六月; liùyuè; 'sixth month', 七月; qīyuè; 'seventh month', 八月; bāyuè; 'eighth month', 九月; jiǔyuè; 'ninth month', 十月; shíyuè; 'tenth month', 冬月; dōngyuè; 'eleventh month', and 臘月; 腊月; làyuè; 'end-of-year month'.
• Intercalary months: Intercalary months are added seven times every 19 years to keep the calendar aligned with the solar year. Intercalary months are added in years with a new moon falling between the winter solstice and the following spring equinox.
• Gan-Zhi cycle: The 60-year Gan-Zhi cycle plays an important role in the calendar and is used to name years, predict fortunes, and choose auspicious dates for important events. Each year in the cycle is associated with a specific animal, forming the famous 12-animal zodiac.

History
The origins of the Chinese calendar can be traced back to the Shang Dynasty (1600-1046 BCE), where early forms of calendars based on lunar cycles were used for agricultural purposes. Over time, the calendar became more sophisticated, incorporating elements of solar cycles and astronomical observations. The Qin Dynasty (221-206 BCE) standardized the calendar, establishing a system that was largely based on the lunar cycle but included intercalary months to keep it aligned with the solar year. The Han Dynasty (206 BCE-220 CE) further refined the calendar, introducing the 60-year cycle known as the Gan-Zhi system, which combines 10 Heavenly Stems and 12 Earthly Branches to create unique combinations for each year. The Chinese calendar continued to evolve through the centuries, with various emperors and dynasties making adjustments and refinements. The modern Chinese calendar, officially known as the "Xia calendar," was adopted in 1949 and is still used today.