History and Development of Calendars

A calendar is a system of measuring time based on needs of a daily life; it is split into years, months, weeks, and days. Calendar separations are based on movements of the earth and consistent appearances of the moon and sun.  A solar year is based on one revolution of the earth around the sun, and a lunar year is based on one revolution of the earth around the moon. A solar year has 365 days except on the fourth year which has 366 days, and a lunar year has 354 days. A day is the time the earth takes to rotate about its axis. Initially, a month was calculated by primitive civilizations as the number of days needed for the moon to circle the earth or simply the time between two full moons; this was usually around 29.5 days. In the calendar that most people use today, the month is almost one-twelfth of a year; months can have 30 or 31 days unless it’s February which has 28. The week is also a modern idea; it was obtained from the Judeo-Christian tradition that required a break from work every seventh day (Calendar, 2018).

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Stars and planets provide society with a reference for measuring passages of time; ancient people relied on the motion to make sense of seasons, months, and years. There isn’t much information regarding the details of timekeeping in prehistoric eras, but every time artifacts or records are found since early civilizations came about, researchers have discovered that people in every culture were keeping track of time in some fashion. Over 20,000 years ago, Ice-age hunters scratched lines in sticks animal bones which archaeologist have thought it was the hunters way of keeping track of the days between phases of the moon. Around 5,000 years ago, “Sumerians in the Tigris-Euphrates valley in today’s Iraq had a calendar that divided the year into 30-day months, divided the day into 12 periods (each corresponding to 2 of our hours), and divided these periods into 30 parts (each like 4 of our minutes).” Over 4,000 years ago, Stonehenge was built in England; while no one has figured out the entire meaning of Stonehenge, some people theorize that it was built to determine eclipses and solstices (A Walk Through Time, 2009).
The earliest Egyptian calendar was based on lunar cycles, but Egyptians later found that the “Dog Star” in Canis Major, which is now called Sirius, rose next to the sun every 365 days. They found the “Dog Star” around the time when the annual flooding of the Nile River began. Around 3100 BC, they decided to reform their calendar to follow this pattern. Essentially, they were the first civilization to adopt the solar year. This year seems to be one of the earliest years that is recorded in history. (A Walk Through Time, 2009). However, their version was a little different than the calendar that is used today; it had 365 days which were divided into 12 months, and each month had 30 days. They added the other 5 days at the end of the year. Around 238 BC King Ptolemy III, the third king of the Ptolemaic dynasty in Egypt, declared that an extra day needed to be added to every fourth year (Calendar, 2018).
The ancient Babylonians had a lunisolar calendar which means that they had lunar months but a solar year. They had 12 lunar months which consisted of 30 days each, and they added extra months when the needed their calendar to line up with the seasons (Calendar, 2018). However, another source mentions that used a year that had 354 days and alternated between 29- and 30-day lunar months (A Walk Through Time, 2009). According to Britannica, the Babylonian months were called Nisanu, Ayaru, Simanu, Duʾuzu, Abu, Ululu, Tashritu, Arakhsamna, Kislimu, Tebetu, Shabatu, Adaru respectively. Their days began at sunset and sundials and water clocks were used to keep track of the hours. The Babylonian calendar influenced the Jewish calendar; the Jews adopted their month names and customs dates from the Babylonian Exile period in the 6th century B.C. (The Editors of Encyclopaedia Britannica, 2009).
A lunisolar calendar that was used in ancient Greece also had 354 days in a year. “The Greeks were the first to intercalate extra months into the calendar on a scientific basis, adding months at specific intervals in a cycle of solar years” (Calendar, 2018). Every city-state in Greece had their own version of a calendar which tended to get a bit confusing. The most well-known of the Greek calendars was the Athenian calendar. There were 12 months called Hekatombion, Metageitnion, Boedromion, Pyanepsion, Maimakterion, Poseidon, Gamelion, Anthesterion, Elaphebolion, Munychion, Thargelion, and Skirophorion respectively. When they added a month, it was added as the seventh month and called second Poseidon. The Athenians considered this their festive calendar and had a separate calendar dedicated to politics.  The didn’t have a system for their calendar because they months alternated between 29 and 30 days and corrected it when they realized it wasn’t accurate anymore (Hagen, n.d.).
The calendar system in ancient China was complicated to say the least. During the Warring States period which lasted from 475 to 221 B.C., the quarter calendar was established. They were the first to recognize that one year had 365 and a quarter days. However, nothing was really done to make this calendar system official. In 104 B.C, a calendar in China was finally made official by Emperor Han Wu and started being adopted by the majority of people. Similar to the quarter calendar, there were 365 and days in a year and 29 days in a month. The calendar usually went through reforms every time there was a new emperor. One of the changes was the year started over at zero again. The last time the calendar system started over was the Qing Dynasty during Emperor Qian Long’s rule. This became the current Chinese calendar which starts at the year 1723. To this day, the Chinese calendar is continuously being changed when astronomers recognize a discrepancy. The calendar is a big part of Chinese culture of which they are proud. They celebrate Chinese New Year and several other holidays that are specific to their culture. They use the western calendar for business affairs since that is what most countries use (The Epoch Times Staff, 2010).
The Mayans relied on the sun, moon, and Venus to establish two calendars, one with 260 days and the other with 365 days. The most well-known was called the Long Count Calendar. It became important to them to measure the past as well as the present and future, so this system was used to date mythical and historical events in chronological order. This is one of the longest cycles in the Mayan calendar system, measuring over 5,125 years or 1,872,000 days. They believed the creation of the world took place in 3114 BC and left tremendous amounts of celestial-cycle records behind explaining their reasoning. Between 2600 BC and 1500 AD, their culture and ways of timekeeping spread to their related predecessors across Central America which the most prevalent spread happening between 250 and 900 A.D. Later their calendars became a part of the famous Aztec calendar stones. The Mayans have influenced today’s society as well with their timekeeping systems. The Long Count Calendar ended on the winter solstice on December 21, 2012 and led many to believe that the Mayans had predicted the end of the world when in fact, it was just the end of a cycle (A Walk Through Time, 2009) (The Calendar System, n.d.).
The Roman calendar originated as a local calendar for the city of Rome, drawn up by Romulus around 800-700 BC. The year consisted of 10 months, starting in March and ending in December. It had six months with 30 days and the other four had 31 days, which totaled to 304 days. The winter season went unaccounted for. Numa Pompilius added January and February to the end of the year to give dates to the winter gap. This made the year add to 354 days. However, Pompilius realized the new months didn’t have enough days in them, so he took one day from each of the 30-day months. This gave him 56 days to divide between the two months. The Romans had a superstition against even numbers, so January was given the odd amount of days, and February had an even number of days. They decided to dedicate the month to the gods, which made them feel better about the month having an even number of days. The system allowed the year of 12 months to have 355 days, an odd number. March, May, July, and October had 31 days; January, April, June, August, September, November, and December had 29 days while February had 28 (The Roman Calendar, n.d.). 
The Roman Republican calendar was introduced by the Etruscan Lucius Tarquinius Priscus because he wanted the year to start in January since it contained the festival of the god of gates, but the Etruscan dynasty collapsed in 510 BC which led to the reform to be dropped. It was a lunar calendar that was short by 10.25 days of a 365.25-day solar year. “In order to prevent it from becoming too far out of step with the seasons, an intercalary month, Intercalans, or Mercedonius (from merces, meaning wages, since workers were paid at this time of year), was inserted between February 23 and 24. It consisted of 27 or 28 days, added once every two years, and in historical times at least, the remaining five days of February were omitted” (The Editors of Encyclopaedia Britannica, 2009).
The purpose of the calendar is to reckon past or future time, to show how many days until a certain event takes place, or how long since something important happened. Without Calendars, society would not be able to function. Everything would change. We wouldn’t be able to assign time. We wouldn’t know what day it is because not only would we not be able to keep track, but we wouldn’t even be able to comprehend what a day is. We might know to meet someone when the sun comes up again, but how would we meet someone a week from now? Unless someone writes it down, keep track of the day would be difficult. Keeping track of dates is precisely the purpose of a calendar. “A calendar is convenient for regulating civil life and religious observances and for historical and scientific purposes” (The Editors of Encyclopaedia Britannica, 2009).
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