Calendar

What has the Roman dodecahedron to do with our calendar?

In this column, I will explain why the dodecahedron was used for accurate date calculation whereas at that point, they were using Julian calendar for over one hundred years.

The origin of agriculture

The need of an accurate calendar arrangement will probably be arisen at the moment that mankind made the transition of being a hunter/collector to being a farmer. As long as he was dependent on nature for his food, a calendar was almost useless. Just like now, nature can be whimsical and unpredictable. After all, every year we read newspaper articles of warmth or cold records that are being broken. Despite of our weather satellites, it remains difficult to predict the weather for periods further away.

It would be a great asset for agriculture if we could predict weather for longer periods. After all, it is of a great importance for the moment a farmer should sow or harvest. Our earliest ancestors will probably have realized this when they graduately changed from being a hunter to getting a staying in permanent housing where food supply was largely dependent on the production of grain. Because nature is unpredictable, they were looking for a moment at which the yields would be as large as possible. Because of this, they were forced to make some sort of calendar. Just relying on nature would have been a large risk. As nature showed larger differences in temperature and in rainfall, choosing the exact date became more important.

Therefore, making a calendar for a tropic forest would be of less importance than in North-Western Europe where the difference in temperature on a yearly basis can add up to 40 ° C.

The solar year as a calendar

The climate differences in North-Western Europe compared to Southern Europe will also have been noticed by Julius Caesar when he got acquainted with the tough winters when he went into North-Western Europe for his conquests.

Especially the sowing time of winter grains became very important to guarantee optimal yields because of the severe winters. To ensure the food supply for Caesar’s army, an accurate calendar regulation based on the solar year was important.

Thereupon, Julius introduced calendar reformation around 46 BC, that resembles our current calendar. This calendar reformation, that we started to call the Julian calendar, was based on the assumption that a solar year was 365,25 days. To make the calendar having the same rhythm as the actual solar year, a leap year had to be introduced every fourth year. The problem occurs that the time when our planet earth needs to rotate around its own axes (a single day), has nothing to do with the time earth needs to travel completely around the sun (this is called a solar year). This time is not 365,25 but 365,242199 days. The actual solar year elapses faster than the Julian calendar. The error in this calendar caused a deviation of one day every 128 year. Around 80 AD, the Romans would have noticed this error for the first time. That would be the time that the first dodecahedrons were made. With these dodecahedrons, they could determine the best day for sowing that during autumn time without having to use the existing calendar. The accuracy of the dodecahedron was dependent on the angle of the sun, which will stay the same with a maximal deviation of a mere one day over thousands of years.

In 325 AD, the calendar was adapted. During the reign of Julius Caesar, the vernal equinoctial point was on March 25. In 325 AD, this vernal equinoctial point was shifted to March 21.

In that year, over 250 bishops came together at Nicaea to discuss the increasing problems concerning the date of Eastern. At this meting, they decided that from that point on, March 21 would be the vernal equinoctial point, which would mean that the calendar would have the same pace as the solar year. The last dodecahedrons descend from the fourth century AD.

Because of the collapse of the Roman empire, the dodecahedron has probably gotten in disuse. The error in the Julian calendar ran again up to about 10 days in 1582.

This error was rectified in 1582 by pope Gregorius XIII by deciding that after October 4 1582, the day October 15 1582 would follow. Thereupon, they decided that that every year that would be divisible by four, would be a leap year without the exception of the century years that were not divisible by four. This means that 1900 was no leap year but the year 2000 was, and the year 2100 will not be a leap year. This calendar is still in use and is called the Gregorian calendar.