The calendar is a method whereby people mesure time for civil or religious purposes, dividing it into years, months, weeks and days.

We know that the regular, apparent movement of the Sun across the sky is caused by the Earth’s rotation. A day is the time taken by the Earth to revolve on its axis, just under twenty four hours.
The Latin word for the Moon is Luna and the time between two new moons is about twenty eight days, the Lunar month The Solar year is the time taken by the Earth to travel around the Sun – 365 days, 5 hours and forty eight minutes 46 seconds.

Because these lengths of time do not add up to round numbers, and because Lunar months do not fit into Solar years, it took a number of centuries before a calendar was developed that did not have to be adjusted every year.

The Egyptian calendar was the first fairly accurate attempt to measure the year’s length. This goes back about 4,000 years B.C. They had noted that the river Nile overflowed its banks at the same time every year and that at the time of the flood the dog star Sirius rose just at sunrise.

They carefully counted the days until this happened again and found that it was 365 days. This is the approximate length of a year and the Egyptians divided it into twelve months of thirty days each, with five extra days at the end of the year.

Greeks, Assyrians, Jews, Muslims, Chinese, the many civilisations, each developed their own calendar, and in each case the time was measured, from some outstanding historical event.
The Romans took their starting point as the time of the foundation of Rome about 753 B.C., and the Muslim calendar starts from the flight of Mohammed from Mecca, called the Hegira, which took place about 622 A.D.

Christians believe that the birth of Christ is the most outstanding historical event and they label time either B.C., which means before Christ, or A.D., which means Anno Domini, the year of the Lord after the birth of Christ.

The calendar we use today is based on the calendar designed by Julius Caesar and is called the Julian calendar. Before that, the Romans had a calendar of ten months containing 304 days.
King Pompilius added two more months, Januarius and Februarius, which brought the number of days up to 355, as the Romans believed that the even numbers represented death,and odd ones life. All the months had 29 or 31 days, except February, which had 28 days.

To make this year agree with the Solar year, the politicians and priests added extra months whenever they wanted to. Consequently, the calendar soon became a complete muddle.

In the year 46 B.C., Julius Caesar decided that the number of days in each year should be 3651/4, which seemed to be the exact length of the Solar year. In order to get things straight before he brought in this new calendar, Caesar ordered that 46 B. C. should have 445 days, and that year became known as “the year of confusion”.

The years after that had 365 days each, except every fourth year. To use up the quarter of a day left over from each ordinary year, every fourth year had 366 days and became known as ‘leap year’.

He made five months 30 days long and six months 31 days long, and he gave February 29 days in an ordinary year and 30 in leap years.

But the priests made the mistake of adding an extra day to February every third year instead of every fourth. Augustus Caesar corrected this accumulated error and decreed that the month which followed ‘Julius’ should be named ‘Augustus’ and, in addition, a day was taken from the month of February and given to Augustus (August).

The Julian year was about 11 minutes longer than the actual year, and though 11 minutes may not seem much, the 11 minutes a year grew into days as the centuries went by.

In the 16th century, the error in the Julian calendar amounted to ten days, and Church Festivals like Christmas and Easter were so much out of place that Pope Gregory XIII ordered ten days to be dropped from the year 1582. To keep the calendar correct in the future the Pope asked that ‘leap year’ should be left out of the last year of every century, unless the number of that year could be divided by 400.

This system is called the Gregorian calendar. The Roman Catholic countries adopted the Gregorian calendar almost at once, but the Protestant countries like Holland and England were slower to accept it.

Great Britain continued to use the Julian calendar until 1752, and by that time the error in the Julian calendar amounted to eleven days. So in 1752 the 14th September was declared to be ‘the day after the second’, that is the third day of September, and because so many people did not understand this new arrangement they rioted in the streets in England and shouted “give us back our eleven days!”

The eastern European countries did not adopt the Gregorian calendar until early in this present century. In Bulgaria they adopted the system in 1916, Russia did in 1918, and the Greek Orthodox Church in 1924.

Centre: Aztec Calendar Stone.
Clockwise: Not an egg whisk, but a Byzantine representation of the solar system; a clay tablet recording the phases of the moon; Pope Gregory XIII (on throne) at the meeting which devised the Gregorian Calendar; a Saint’s Calendar for the first half of August, showing Summer games, from the late-15th century.