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Calendar: the story on HearLore | HearLore
Calendar
The word calendar originates from the Latin term calendar, which meant the first day of the month in the Roman calendar, derived from the verb to call out. This ancient verb referred to the public calling of the new moon when it was first seen in the sky, marking the beginning of a new month. In the Roman system, the calends were the days when accounts were settled and debts were collected, turning the calendar into an account book or register. This etymological root reveals that the calendar was not merely a tool for tracking time but a mechanism for social and economic order, binding the community through the rhythmic calling of the moon. The term entered the English language through Old French as calender and Middle English as calendar by the 13th century, preserving the ancient connection between the celestial cycle and human obligation. The earliest physical calendars emerged in the Ancient Near East, where the development of writing allowed the Bronze Age Egyptians and Sumerians to record time in a permanent form. These early systems were deeply tied to the observation of the sun and moon, the most salient recurring natural events useful for timekeeping in pre-modern societies. The Roman calendar itself contained remnants of a very ancient pre-Etruscan 10-month solar year, showing how timekeeping evolved from simple observation to complex social structure. The first recorded physical calendars were dependent on the development of writing, marking a pivotal moment in human history when the abstract concept of time became a tangible record. The Roman calendar was reformed by Julius Caesar in 46 BC, creating the Julian calendar which was no longer dependent on the observation of the new moon but followed an algorithm of introducing a leap day every four years. This reform created a dissociation of the calendar month from lunation, shifting the focus from the moon to the sun and establishing a more predictable system for the Roman Empire. The Gregorian calendar, introduced in 1582, corrected most of the remaining difference between the Julian calendar and the solar year, refining the system to better align with the Earth's orbit. The Islamic calendar, based on the prohibition of intercalation by Muhammad, resulted in an observation-based lunar calendar that shifts relative to the seasons of the solar year, a decision made in a sermon given on 9 Dhu al-Hijjah AH 10, which corresponds to the Julian date of the 6th of March 632. This decision created a calendar that drifts 11 or 12 days each year, causing Islamic holy days to cycle through all seasons over a period of approximately 33 Islamic years. The history of the calendar is a story of human attempts to impose order on the chaotic cycles of nature, from the calling of the new moon to the precise algorithms of the modern Gregorian calendar.
The Sun, The Moon, And The Year
Common questions
What is the origin of the word calendar?
The word calendar originates from the Latin term calendar, which meant the first day of the month in the Roman calendar, derived from the verb to call out. This ancient verb referred to the public calling of the new moon when it was first seen in the sky, marking the beginning of a new month.
When was the Gregorian calendar introduced?
The Gregorian calendar was introduced in 1582 as a refinement to the Julian calendar. It corrected most of the remaining difference between the Julian calendar and the solar year, refining the system to better align with the Earth's orbit.
What is the Islamic calendar based on?
The Islamic calendar is based on the prohibition of intercalation by Muhammad, resulting in an observation-based lunar calendar that shifts relative to the seasons of the solar year. This decision was made in a sermon given on 9 Dhu al-Hijjah AH 10, which corresponds to the Julian date of the 6th of March 632.
Who created the Julian calendar?
The Roman calendar was reformed by Julius Caesar in 46 BC, creating the Julian calendar. This reform created a dissociation of the calendar month from lunation, shifting the focus from the moon to the sun and establishing a more predictable system for the Roman Empire.
Which country was the last to adopt the Gregorian calendar?
The last European country to adopt the Gregorian calendar was Greece, in 1923. During the Early Modern period, its adoption was mostly limited to Roman Catholic nations, but by the 19th century it had become widely adopted for the sake of convenience in international trade.
The course of the sun and the moon are the most salient regularly recurring natural events useful for timekeeping, and in pre-modern societies around the world lunation and the year were most commonly used as time units. 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 built a calendar with 365 days, divided into 12 months of 30 days each, with 5 extra days at the end of the year. However, they did not include the extra bit of time in each year, and this caused their calendar to slowly become inaccurate. This inaccuracy was a significant flaw, as the calendar drifted by one day every four years, eventually causing the calendar to fall out of sync with the seasons. The lunar calendar, in which days are numbered within each lunar phase cycle, quickly drifts against the seasons because the length of the lunar month is not an even fraction of the length of the tropical year. Alexander Marshack, in a controversial reading, believed that marks on a bone baton represented a lunar calendar, while Michael Rappenglueck believes that marks on a 15,000-year-old cave painting represent a lunar calendar. These controversial interpretations suggest that the human desire to track time may date back to the Paleolithic era, long before the development of writing. The lunisolar calendar is a lunar calendar that compensates by adding an extra month as needed to realign the months with the seasons. Prominent examples of lunisolar calendars are the Hindu calendar and the Buddhist calendar that are popular in South Asia and Southeast Asia. Another example is the Hebrew calendar, which uses a 19-year cycle to keep the lunar months in sync with the solar year. The week cycle is an example of one that is not synchronized to any external phenomenon, although it may have been derived from lunar phases, beginning anew every month. The seven-day week is practically universal, though its use varies, and it has run uninterrupted for millennia. The vast majority of calendar systems track years, months, weeks, and days, incorporating more complex cycles to provide a comprehensive system for organizing time. The Gregorian calendar, the de facto international standard, uses a cycle of leap days in a 400-year cycle designed to keep the duration of the year aligned with the solar year. There is a lunar aspect which approximates the position of the moon during the year, and is used in the calculation of the date of Easter. Each Gregorian year has either 365 or 366 days, amounting to an average Gregorian year of 365.2425 days, compared to a solar year of 365.2422 days. The calendar is a complex system that balances the cycles of the sun and the moon, the needs of agriculture, and the requirements of religious observance. The history of the calendar is a testament to human ingenuity, as we have developed systems to track time from the simple observation of the moon to the precise algorithms of the modern Gregorian calendar. The calendar is a tool that has evolved over thousands of years, reflecting the changing needs and understanding of human society. The calendar is a system that organizes days, giving names to periods of time, typically days, weeks, months, and years, and a date is the designation of a single and specific day within such a system. The calendar is also a physical record, often paper, of such a system, and can also mean a list of planned events, such as a court calendar, or a partly or fully chronological list of documents, such as a calendar of wills. The calendar is a system that has been used for thousands of years, and it continues to evolve to meet the needs of modern society. The calendar is a system that organizes days, giving names to periods of time, typically days, weeks, months, and years, and a date is the designation of a single and specific day within such a system. The calendar is also a physical record, often paper, of such a system, and can also mean a list of planned events, such as a court calendar, or a partly or fully chronological list of documents, such as a calendar of wills.
The Algorithm Of Time
Calendars that contain one level of cycles include the week and weekday, which is not very common, and the year and ordinal date within the year, such as the ISO 8601 ordinal date system. Calendars with two levels of cycles include the year, month, and day, which is the most common system, including the Gregorian calendar and its very similar predecessor, the Julian calendar, the Islamic calendar, the Solar Hijri calendar, and the Hebrew calendar. Calendars with two levels of cycles also include the year, week, and weekday, such as the ISO week date. The simplest calendar system just counts time periods from a reference date, or epoch, which applies for the Julian day or Unix Time. Virtually the only possible variation is using a different reference date, in particular, one less distant in the past to make the numbers smaller. Computations in these systems are just a matter of addition and subtraction. An astronomical calendar is based on ongoing observation, such as the religious Islamic calendar and the old religious Jewish calendar in the time of the Second Temple. Such a calendar is also referred to as an observation-based calendar. The advantage of such a calendar is that it is perfectly and perpetually accurate. The disadvantage is that working out when a particular date would occur is difficult. An arithmetic calendar is one that is based on a strict set of rules, such as the current Jewish calendar. Such a calendar is also referred to as a rule-based calendar. The advantage of such a calendar is the ease of calculating when a particular date occurs. The disadvantage is imperfect accuracy. Furthermore, even if the calendar is very accurate, its accuracy diminishes slowly over time, owing to changes in Earth's rotation. This limits the lifetime of an accurate arithmetic calendar to a few thousand years. After then, the rules would need to be modified from observations made since the invention of the calendar. The early Roman calendar, created during the reign of Romulus, lumped the 61 days of the winter period together as simply winter. Over time, this period became January and February, through further changes over time, including the creation of the Julian calendar, this calendar became the modern Gregorian calendar, introduced in the 1570s. The Gregorian calendar was introduced in 1582 as a refinement to the Julian calendar, that had been in use throughout the European Middle Ages, amounting to a 0.002% correction in the length of the year. During the Early Modern period, its adoption was mostly limited to Roman Catholic nations, but by the 19th century it had become widely adopted for the sake of convenience in international trade. The last European country to adopt it was Greece, in 1923. The calendar epoch used by the Gregorian calendar is inherited from the medieval convention established by Dionysius Exiguus and associated with the Julian calendar. The year number is variously given as AD, for Anno Domini, or CE, for Common Era or Christian Era. The calendar is a system that has been used for thousands of years, and it continues to evolve to meet the needs of modern society. The calendar is a system that organizes days, giving names to periods of time, typically days, weeks, months, and years, and a date is the designation of a single and specific day within such a system. The calendar is also a physical record, often paper, of such a system, and can also mean a list of planned events, such as a court calendar, or a partly or fully chronological list of documents, such as a calendar of wills. The calendar is a system that has been used for thousands of years, and it continues to evolve to meet the needs of modern society.
The Sacred And The Secular
The most important use of pre-modern calendars is keeping track of the liturgical year and the observation of religious feast days. 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, Lent, Easter, and Ordinary Time. Some Christian calendars do not include Ordinary Time and every day falls into a denominated season. The Eastern Orthodox Church employs the use of 2 liturgical calendars, the Julian calendar, often called the Old Calendar, and the Revised Julian Calendar, often called the New Calendar. The Revised Julian Calendar is nearly the same as the Gregorian calendar, with the addition that years divisible by 100 are not leap years, except that years with remainders of 200 or 600 when divided by 900 remain leap years, such as 2000 and 2400 as in the Gregorian 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 Hijra, corresponding to AD 622. With an annual drift of 11 or 12 days, the seasonal relation is repeated approximately every 33 Islamic years. Various Hindu calendars remain in use in the Indian subcontinent, including the Nepali calendars, Bengali calendar, Malayalam calendar, Tamil calendar, Vikrama Samvat used in Northern India, and Shalivahana calendar in the 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 and subsequently reformed by astronomers such as Aryabha (AD 499), Varahamihira (6th century) and Bhaskara II (12th century). The Hebrew calendar is used by Jews worldwide for religious and cultural affairs, also influences civil matters in Israel, such as national holidays, and can be used in business dealings, such as for the dating of cheques. Followers of the Bahai Faith use the Bahai calendar. The Bahai Calendar, also known as the Badi Calendar was first established by the Bab in the Kitab-i-Asma. The Bahai Calendar is also purely a solar calendar and comprises 19 months each having nineteen days. The calendar is a system that has been used for thousands of years, and it continues to evolve to meet the needs of modern society. The calendar is a system that organizes days, giving names to periods of time, typically days, weeks, months, and years, and a date is the designation of a single and specific day within such a system. The calendar is also a physical record, often paper, of such a system, and can also mean a list of planned events, such as a court calendar, or a partly or fully chronological list of documents, such as a calendar of wills. The calendar is a system that has been used for thousands of years, and it continues to evolve to meet the needs of modern society.
The Calendar Of Nations
The Chinese, Hebrew, Hindu, and Julian calendars are widely used for religious and social purposes. The Iranian calendar is used in Iran and some parts of Afghanistan. The Assyrian calendar is in use by the members of the Assyrian community in the Middle East, mainly Iraq, Syria, Turkey, and Iran, and the diaspora. The first year of the calendar is exactly 4750 years prior to the start of the Gregorian calendar. The Ethiopian calendar or Ethiopic calendar is the principal calendar used in Ethiopia and Eritrea, with the Oromo calendar also in use in some areas. In neighboring Somalia, the Somali calendar co-exists alongside the Gregorian and Islamic calendars. In Thailand, where the Thai solar calendar is used, the months and days have adopted the western standard, although the years are still based on the traditional Buddhist calendar. The calendar is a system that has been used for thousands of years, and it continues to evolve to meet the needs of modern society. The calendar is a system that organizes days, giving names to periods of time, typically days, weeks, months, and years, and a date is the designation of a single and specific day within such a system. The calendar is also a physical record, often paper, of such a system, and can also mean a list of planned events, such as a court calendar, or a partly or fully chronological list of documents, such as a calendar of wills. The calendar is a system that has been used for thousands of years, and it continues to evolve to meet the needs of modern society. The calendar is a system that organizes days, giving names to periods of time, typically days, weeks, months, and years, and a date is the designation of a single and specific day within such a system. The calendar is also a physical record, often paper, of such a system, and can also mean a list of planned events, such as a court calendar, or a partly or fully chronological list of documents, such as a calendar of wills. The calendar is a system that has been used for thousands of years, and it continues to evolve to meet the needs of modern society.
The Fiscal And The Digital
A fiscal calendar generally means the accounting year of a government or a business. It is used for budgeting, keeping accounts, and taxation. It is a set of 12 months that may start at any date in a year. The US government's fiscal year starts on the 1st of October and ends on the 30th of September. The government of India's fiscal year starts on the 1st of April and ends on the 31st of March. Small traditional businesses in India start the fiscal year on Diwali festival and end the day before the next year's Diwali festival. In accounting, and particularly accounting software, a fiscal calendar, such as a 4/4/5 calendar, fixes each month at a specific number of weeks to facilitate comparisons from month to month and year to year. January always has exactly 4 weeks, February has 4 weeks, March has 5 weeks, etc. Note that this calendar will normally need to add a 53rd week to every 5th or 6th year, which might be added to December or might not be, depending on how the organization uses those dates. There exists an international standard way to do this, the ISO week. The ISO week starts on a Monday and ends on a Sunday. Week 1 is always the week that contains the 4th of January in the Gregorian calendar. The calendar is a system that has been used for thousands of years, and it continues to evolve to meet the needs of modern society. The calendar is a system that organizes days, giving names to periods of time, typically days, weeks, months, and years, and a date is the designation of a single and specific day within such a system. The calendar is also a physical record, often paper, of such a system, and can also mean a list of planned events, such as a court calendar, or a partly or fully chronological list of documents, such as a calendar of wills. The calendar is a system that has been used for thousands of years, and it continues to evolve to meet the needs of modern society. The calendar is a system that organizes days, giving names to periods of time, typically days, weeks, months, and years, and a date is the designation of a single and specific day within such a system. The calendar is also a physical record, often paper, of such a system, and can also mean a list of planned events, such as a court calendar, or a partly or fully chronological list of documents, such as a calendar of wills. The calendar is a system that has been used for thousands of years, and it continues to evolve to meet the needs of modern society.
The Format Of Time
The term calendar applies not only to a given scheme of timekeeping but also to a specific record or device displaying such a scheme, for example, an appointment book in the form of a pocket calendar, desktop calendar, a wall calendar, etc. In a paper calendar, one or two sheets can show a single day, a week, a month, or a year. If a sheet is for a single day, it easily shows the date and the weekday. If a sheet is for multiple days it shows a conversion table to convert from weekday to date and back. With a special pointing device, or by crossing out past days, it may indicate the current date and weekday. This is the most common usage of the word. In the US Sunday is considered the first day of the week and so appears on the far left and Saturday the last day of the week appearing on the far right. In Britain, the weekend may appear at the end of the week so the first day is Monday and the last day is Sunday. The US calendar display is also used in Britain. It is common to display the Gregorian calendar in separate monthly grids of seven columns, from Monday to Sunday, or Sunday to Saturday depending on which day is considered to start the week, this varies according to country, and five to six rows, or rarely, four rows when the month of February contains 28 days in common years beginning on the first day of the week, with the day of the month numbered in each cell, beginning with 1. The sixth row is sometimes eliminated by marking 23/30 and 24/31 together as necessary. When working with weeks rather than months, a continuous format is sometimes more convenient, where no blank cells are inserted to ensure that the first day of a new month begins on a fresh row. Calendaring software provides users with an electronic version of a calendar, and may additionally provide an appointment book, address book, or contact list. Calendaring is a standard feature of many PDAs, EDAs, and smartphones. The software may be a local package designed for individual use, such as the Lightning extension for Mozilla Thunderbird, Microsoft Outlook without Exchange Server, or Windows Calendar, or maybe a networked package that allows for the sharing of information between users, such as Mozilla Sunbird, Windows Live Calendar, Google Calendar, or Microsoft Outlook with Exchange Server. The calendar is a system that has been used for thousands of years, and it continues to evolve to meet the needs of modern society. The calendar is a system that organizes days, giving names to periods of time, typically days, weeks, months, and years, and a date is the designation of a single and specific day within such a system. The calendar is also a physical record, often paper, of such a system, and can also mean a list of planned events, such as a court calendar, or a partly or fully chronological list of documents, such as a calendar of wills. The calendar is a system that has been used for thousands of years, and it continues to evolve to meet the needs of modern society. The calendar is a system that organizes days, giving names to periods of time, typically days, weeks, months, and years, and a date is the designation of a single and specific day within such a system. The calendar is also a physical record, often paper, of such a system, and can also mean a list of planned events, such as a court calendar, or a partly or fully chronological list of documents, such as a calendar of wills. The calendar is a system that has been used for thousands of years, and it continues to evolve to meet the needs of modern society.