Calendars are very important. Nowadays they are used by everyone. Calendars indicate which day it is and are also important for determining the days on which religious and other festivals or appointments fall.
Before calendars existed
About 2000 years ago, calendars did not exist. People had no idea what kind of day it was, but there were some tricks to find out what time it was. For example, the ancient Egyptians looked at a star called Sirius. When that star rose in the east in the morning, they knew it would not be long before the Nile would flood. This is how the Egyptians knew when it was time to sow and harvest.
The first calendars
The oldest calendars were based on the movement of the moon. During the time that the moon revolves around the earth, we see the different phases of the moon from the earth. This is how the days were determined.
Later the sun was also used by means of sundials. Sundials are the oldest clocks with which people determined the daily time. As the sun moves across the sky, the location and length of the shadow of a stick on the ground changes.
Lunar and solar calendars
Calendars can be divided into two types of groups: the lunar and solar calendars.
The lunar calendar
The lunar calendars were created for a special period, namely the synodic month. A synodic month lasts an average of 29.530590 days. Since it is impossible to have a day of 29.5 days, this problem was solved by alternately entering a month of 29 days and 30 days. The year of the lunar calendar consists of 354 days. A lunar year is approximately 11 days shorter than a tropical year (see The solar calendar), making a lunar calendar independent of the annual orbit of the sun.
The solar calendar
The solar calendar tries to follow a repeating phenomenon of the sun. The calendar is linked to the tropical year. A tropical year is on average 365.2422 days long. Entering leap days ensures a fixed solar year. This ensures that the year falls into a fixed season.
The sun fixes the duration of a year. The Earth moves around the Sun once in about 365.25 days. This period is called the solar year. The problem is that a complete lunar orbit cannot exactly fit into a solar year. There are also not a full number of days in one solar year, which is why leap years are used. A leap year is a year with 366 days, instead of 365. Leap years occur every 4 years. Any year that is divisible by 4 and not 100 is a leap year. An exception is when the year is divisible by 400, then it is again a leap year. The year 2000 was therefore a leap year.
Types of calendars
The Egyptian calendar
The Egyptian calendar was developed in Pharaonic Egypt. This is about 4000 years ago. The Egyptian calendar is a solar calendar and had 365.25 days. The Egyptians divided the night into twelve parts of equal length as early as 2150 BC. The summer nights were shorter and the winter nights longer, so there was an unequal distribution of hours. Around 1350 BC, time was divided into 24 equal hours, as we know them today.
The Egyptian year consisted of twelve months with 30 days each. This means that there were five days left every year. These days were also called epagomena days. Because these days were not part of the days that the gods had created, these extra days were considered ominous by the Egyptians. The Egyptians even had rules of what could and could not be done on these days.
The Alexandrian Calendar
The Alexandrian calendar originated in the year 30 AD. The Romans came to Egypt and forced them to use a leap day every fourth year. The Egyptians still used the Egyptian calendar at the time, but after the introduction of the leap year the calendar was given the name Alexandrian calendar.
The Roman calendar
The Roman calendar was developed by Romulus around 735 BC. Romulus is the first mythical king of Rome. The year of Romulus consisted of 10 months of 304 days in total. The first 4 months of the year were named after important gods:
- The first month was named after Martis;
- The second month to Aprilis;
- The third to Maius;
- The fourth to Junius
The rest of the months were numbered from 5 to 10.
Around 700 BC, King Numa, Roman’s successor , added two months to the Roman calendar: January and February. This ensured that the year consisted of 354 days.
Julian calendar
The Julian calendar was a lunar calendar. In the beginning, this calendar had ten months per calendar year. Mars (March) was the first month of the year. Around 450 BC, leap months were added to the calendar. A year then had 355 days. However, in a number of years the months became confused with the seasons.
Julius Caesar added several intercalary months in 45 BC , making a year 445 days long. In 44 BC he changed the calendar to a solar calendar with 365 days per year. He also changed the Roman calendar. The months had alternating 30 and 31 days, with the exception of February. February had 28 days and in a leap year this became 29.
Islamic calendar
The Islamic calendar is the calendar used in the Islamic faith. This calendar is a lunar calendar that attempts to follow the phases of the moon without regard to the seasons. The month begins with the first appearance of the crescent moon in the evening sky. This is shortly after New Moon. An Islamic year always has twelve months with alternating 30 and 29 days. So a year has 354 or 355 days. The start of the Islamic year is associated with the departure of Muhammad from Mecca to Medina. The Islamic calendar does not use intercalary months, because this is prohibited in Sura The Repentance 37.
The Mayan calendar
The Mayans based their calendar on the cycles of nature, microcosm and macrocosm. They predict the character of days, months and years. Mayans saw time very differently than we do. For them it is a kind of barrier of cause and effect. The Maya use multiple calendars. The most important of these are the Long Count, Haab and Tzolkin Calendar. The Long Count was used for historical purposes, the Haab as a civil calendar and the Tzolkin as a religious calendar. The Tzolkin calendar has 20 days in the first year, 260 days in the second year and 360 days in the third year in a 52-year cycle. On December 21, 2012 our era, the Mayan calendar ended and a new cycle began. The Mayans believed that after the end of a cycle of thousands of years, humanity would move to a higher level. They saw it as some kind of revolutionary development.
The Gregorian calendar
The Gregorian calendar is used by everyone nowadays. There are 12 months in a Gregorian calendar year, each with 30 or 31 days, with the exception of February, which has 28. To ensure that our year continues to correspond with the solar year, the month of February has 29 days once every 4 years. That is a leap year.
Time zone problem
The Gregorian calendar was now used by everyone around the world. Now there was only a time zone problem. The earth rotates on its axis in the direction of the east. That’s why the sun rises later in Berlin than in Moscow and every place had its own time. This was also the case in the Netherlands. This was very difficult for the railway companies and they were therefore the first to be interested in standardizing time. The railway companies set a so-called railway time that was the same throughout the Netherlands.
Technical developments have played an important role in the spread of unit time. In 1901, a wireless signal was sent across the Atlantic Ocean for the first time . As radio continued to develop, the transmitters became stronger and more sensitive. Time signals could now be received anywhere in the world, allowing everyone to adhere to the same standard for time.
Nowadays we use the international time zone system. There are a total of 24 time zones of one hour each. The zero line is located in Greenwich, England. The time in the Netherlands is one hour later than that in Greenwich, we often speak of GMT+1 (Greenwich Mean Time).