The world is inundated with several calendars as there are diverse people and cultural backgrounds. Calendar, as a chart showing days, weeks and months of a year, does not just occur. There are, or there were, several considerations, including superstitions, religious festivals, imperial influences that determined the introduction and use of a particular calendar. PAUL CHIAMA and ANDREW ESSIEN take a look at the origin and features of some popular world calendars.
The Lunar Calendar
The lunar calendar, which best approximated a solar-year calendar was based on a 19-year period. Out of the 19 years, seven years have 13 months and the period stretches into 235 months. Using the lunation method of 29 1/2 days, this sums up to a total of 6, 932 1/2 days. The 19-years, however, summed up to 6, 939.7 days, the difference being one week per period and about five weeks every century.
The 19-year period, even though it requires some adjustment, became the basis of the calendars of ancient Greeks, Babylonians, Jews and Chinese. It was adopted and used by the Arabs until Prophet Muhammad prohibited shifting from 12 to 13 months. This ensured that the Islamic calendar has a lunar year of about 354 days. Consequently, the months of Islamic calendar and Islamic religious festivals shift through all the seasons of the year.
Egyptian Calendar
The ancient Egyptian society was known to have used 12-month calendar of 30 days in each month. This summed up to 360 days in each year. However, at about 4000 BC, Egyptians made addition of five more days at the end of each year to make it conform closely to the solar year. The additional five days later became a period of festival in Egyptian society because it was considered that people should not work in the period because it could bring bad luck.
Egyptians had already taken note that the solar year was closer to 365 1/4 days. Therefore, instead of having a leap day every four years to take the place of the fractional day, they preferred that the 1/4 day should accumulate. What this means is that after a period of 1, 460 solar years or four periods of 365 years, 1, 461 Egyptian years were over. Again, as the years passed, the Egyptian months fell out of season. This brought summer months to fall into winter.
The Roman (Julian) Calendar
At the time it became a world power, Rome, along with the rest of the world, had a particular problem to deal with: making a calendar. The Romans made their problems more difficult because of their superstition. They believed that even numbers were unlucky, and could therefore, be causes of misfortune. Therefore, their months were 29 or 31 days long, except February, which had 28 days.
However, having four months of 31 days, seven months of 29 days, and one month of 28 days which summed up to 355 days, the Romans thought of creating an extra month called Mercedonius which had 22 or 23 days. It was added every second year.
However, the Roman calendar was still too far with the addition of Mercedonius. As a way of making a suitable adjustment to the calendar, an astronomer called Sosigenes gave advice to Julius Caesar on how to handle the calendar conundrum. Caesar then ordered a sweeping reform. Therefore, the year 46 BC was made to have 445 days by imperial decree. This brought the calendar back in place with the seasons. The solar year – with the value of 365 days and six hours – was made the basis of the calendar. The months were 30 or 31 days in length, and to take care of the six hours, every fourth year was made a 366-day year. Moreover, Caesar decreed that the year began with the first of January, not with the vernal equinox in late March.
This calendar was named the Julian calendar, after Julius Caesar. Eastern Orthodox churches have continued to use it for determining holidays to this day. However, despite the correction, the Julian calendar is still 111/2 minutes longer than the actual solar year, and after a number of centuries, even 111/2 minutes adds up.
Gregorian Calendar
In the 15th century, the Julian calendar had shifted behind the solar calendar by about a week. The vernal equinox was, therefore, falling around March 12 instead of around March 20. Then, Pope Sixtus IV (who reigned from 1471 to 1484) called for another reform. A German astronomer, Regiomontanus, was invited to Rome to advise him. The astronomer arrived in 1475, but died shortly afterward. The pope’s plans for reform, therefore, ended abruptly.
In 1545, the Council of Trent authorised Pope Paul III to carry out another reform. Most of the mathematical and astronomical work was done by Father Christopher Clavius, S.J. The immediate correction, advised by Father Clavius and ordered by Pope Gregory XIII, was that Thursday, Oct. 4, 1582, was to be the last day of the Julian calendar. The next day would be Friday, Oct. 15. For long-range accuracy, a formula suggested by the Vatican librarian, Aloysius Giglio was adopted: every fourth year is a leap year unless it is a century year like 1700 or 1800. Century years can be leap years only when they are divisible by 400 (e.g., 1600 and 2000). This rule eliminates three leap years in four centuries, making the calendar sufficiently accurate.
The Gregorian reform was not adopted throughout the West immediately. Most Catholic countries quickly changed to the pope’s new calendar in 1582. But Europe’s Protestant princes chose to ignore the papal bull and continued with the Julian calendar. It was not until 1700 that the Protestant rulers of Germany and the Netherlands changed to the new calendar. In Great Britain (and its colonies) the shift did not take place until 1752, and in Russia a revolution was needed to introduce the Gregorian calendar in 1918. In Turkey, the Islamic calendar was used until 1926.
Despite its widespread use, the Gregorian calendar has a number of weaknesses. It cannot be divided into equal halves or quarters; the number of days per month is haphazard; and months and years may begin on any day of the week. Holidays pegged to specific dates may also fall on any day of the week, and few Americans can predict when Thanksgiving will occur next year. Since Gregory XIII, many other proposals for calendar reform have been made, but none has been permanently adopted. In the meantime, the Gregorian calendar keeps the calendar dates in reasonable unison with astronomical events.
Babylonian Calendar
The Babylonian calendar was a lunisolar calendar with years consisting of 12 lunar months. Each month begins when a new crescent moon is first sighted low on the western horizon at sunset, plus an intercalary month inserted as needed by decree. The calendar is based on a Sumerian predecessor preserved in the Umma calendar of Shulgi (21st century BC).
According to the Babylonian calendar, the year begins in spring, and is divided into reš šatti (“beginning”), mišil šatti (“middle”), and kīt šatti (“end of the year”). The word for “month” was arḫu. During the 6th century BC Babylonian exile of the Hebrews, the Babylonian month names were adopted into the Hebrew calendar. The Assyrian calendar used in Iraq and the Levant also uses many of the same names for its months, such as Iyyar, Tammuz, Ab, Elul, Tishri, and Adar.
Indian (Hindu) Calendar
Hindu calendar is a collective name for most of the luni-sidereal calendars and sidereal calendars traditionally used in Hinduism.
The Hindu calendars are believed to have undergone many changes in the process of regionalisation. Some of the more prominent regional Hindu calendars include the Nepali calendar, Punjabi calendar, Bengali calendar, Malayalam calendar, Tamil calendar, Vikrama Samvat used in Northern India, and Shalivahana calendar in the Deccan States of Karnataka, Telangana, Maharashtra and Andhra Pradesh. The common feature of many regional Hindu calendars is that the names of the 12 months are the same (because the names are based in Sanskrit). The month which starts the year also varies from region to region.
Most of the Hindu calendars were derived from Gupta era astronomy as developed by Āryabhaa and Varāhamihira in the 5th to 6th century. These in turn were based in the astronomical tradition of Vedāga Jyotia, which in the preceding centuries had been standardised in a number of (non-extant) works known as Sūrya Siddhānta. Regional diversification took place in the medieval period. The astronomical foundations were further developed in the medieval period, notably by Bhāskara II (12th century).
Chinese Calendar
The Chinese calendar is a lunisolar calendar. It arranges the year, month and day number upon the astronomical date. It is used for traditional activities in China and by Chinese communities overseas. It sets the date for the Chinese traditional holidays, and guides Chinese people in choosing the lucky day of a wedding or funeral, for opening a venture, or a relocation.
Days in the Chinese calendar begin and end at midnight. Also, months begin on the day with the dark (new) moon while the years begin with the dark moon near the midpoint between winter solstice and spring equinox. The solar terms are the important components of the Chinese calendar. There are one or two, and occasionally three, solar terms within a month.
The present Chinese calendar is the product of evolution. Many astronomical and seasonal factors were added by ancient scientists, and people can reckon the date of natural phenomena such as the moon phase and tide upon the Chinese calendar. In Korea, Vietnam, and the Ryukyu Islands, the Chinese calendar was adopted completely. In Japan, the Chinese calendar was used before the Edo period, and the later Japanese calendar used the algorithm of the Chinese calendar.
However, till date, the official calendar in China is the Gregorian calendar, but the traditional Chinese calendar has not been phased out because it plays an important role. The official name of the Chinese calendar is the Rural Calendar.
Cosmic Calendar
The Cosmic Calendar is a method to visualise the vast history of the universe in which its 13.8 billion year lifetime is condensed down into a single year. In this visualisation, the Big Bang took place at the beginning of January 1 at midnight, and the current moment is mapped onto the end of December 31 at midnight.
At this scale, there are 438 years per second, 1.58 million years per hour, and 37.8 million years per day. This concept was popularised by Carl Sagan in his book The Dragons of Eden and on his television series Cosmos. In the 2014 sequel series, Cosmos: A Spacetime Odyssey, host Neil deGrasse Tyson presents the same concept of a Cosmic Calendar, but using the revised age of the universe of 13.8 billion years as an improvement on Sagan’s 1980 figure of 15 billion years. Sagan goes on to extend the comparison in terms of surface area, explaining that if the Cosmic Calendar is scaled to the size of a football field, then “all of human history would occupy an area the size of his hand”.
Mesoamerican calendars
Mesoamerican calendars are the calendrical systems devised and used by the pre-Columbian cultures of Mesoamerica. Besides keeping time, Mesoamerican calendars were also used in religious observances and social rituals, such as for divination.
The existence of Mesoamerican calendars was known as early as 500 BCE, with the essentials already appearing fully defined and functional. These calendars are still used today in the Guatemalan highlands, Veracruz, Oaxaca and Chiapas, Mexico.
Macedonian calendar
The Ancient Macedonian calendar is a lunisolar calendar that was in use in ancient Macedon in the 1st millennium BC. It consisted of 12 synodic lunar months, which is 354 days per year, which needed intercalary months to stay in step with the seasons. By the time the calendar was being used across the Hellenistic world, seven total embolimoi (intercalary months) were being added in each 19-year Metonic cycle.
The names of the ancient Macedonian Calendar remained in use in Syria even into the Christian era. The Macedonian calendar was in essence the Babylonian calendar with the substitution of Macedonian names for the Babylonian ones. An example of 6th century AD inscriptions from Decapolis, Jordan, bearing the Solar Macedonian calendar, starts from the month Audynaeus. The solar type was merged later with the Julian calendar.
Hellenic Calendar
The Hellenic calendar came into being when there was no uniform calendar imposed upon all of Classical Greece. It began in most Greek states between Autumn and Winter except the Attic calendar, which began in Summer.
The Greeks, as early as the time of Homer, appear to have been familiar with the division of the year into the 12 lunar months but no intercalary month Embolimos or day is then mentioned. Independent of the division of a month into days, it was divided into periods according to the increase and decrease of the moon.
Thus, the first day or new moon was called Noumenia. The month in which the year began, as well as the names of the months, differed among the states, and in some parts even no names existed for the months, as they were distinguished only numerically, as the first, second, third, fourth month, etc.
Of primary importance for the reconstruction of the regional Greek calendars is the calendar of Delphi, because of the numerous documents found there recording the manumission of slaves, many of which are dated both in the Delphian and in a regional calendar.
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