Calendar design is not a simple matter. Tropical year does not consist of the total number of days of sunshine, hence the problem of a leap year.
– Calendar serves the purpose to count days and to drive the sense of time in the long run. We have some natural unit of time, which result from the construction of nature: it is a sunny day, it is the cycle of the moon phase changes and changes in seasons – explains Assoc. Ilona Bednarek from the Department of Astrophysics and Cosmology at the University of Silesia.
The calendar used in Europe trying to connect two different units of time – a unit of Earth’s rotation on its axis – so the day – and the period associated with the changes of the seasons – so the year tropical, ie the interval between two successive równonocami spring. – A tropical year is not composed of the total number of days. This causes a lot of different problems – emphasizes the expert.
It all started between the fourth and third millennia BC, in ancient Egypt. Egyptian priests knew the length of the tropical year approximately. They already knew that it was 365 days, plus approx. One fourth day. – Was due to the observation of the so-called. heliakalnego east Sirius – says Ilona Bednarek. However, not all ancient calendars were accurate: some much rozmijały the length of the tropical year. For example. In ancient Rome there was a moment when the calendar counted 355 days. – I caused a huge problem with the count of days. The Romans had such rule that was added after the Feb. 23 one month, which counted 22 or 23 days. A month was not added regularly.
Julius Caesar, in 45 BC He decided to introduce a new calendar. Calendar consisted of 365 days, and every four years a leap year was introduced. February had then count 29 days. – Over time, the assumption that a leap year is the one that divided divisible by 4. This is called the Julian calendar. But I was not perfect – says Dr. Bednarek. – The average length of the year, calculated according to this calendar is 11 minutes and 14 seconds longer than the tropical year. This caused further problems.
At the Council of Nicaea in 325 AD established rules for determining the date of Easter – was supposed to be Sunday after the first full moon of spring. But to know who is the fullness of spring, it was necessary knowledge about when the equinox falls. – While initially it was on March 21, is due to the difference between the length of the Julian year and the length of the tropical year, the date of the equinox is constantly moved. For example. In the sixteenth century. Date coincided with the equinox on March 11 – explained Ilona Bednarek. That is why Pope Gregory XIII decreed in 1582 calendar reform. It boiled down to two basic principles: it was necessary to restore its former date of Easter and we had to change the average length of the calendar year so that as well people fit the length of the tropical year. To date equinox move on March 21, was shortened by 10 days a year – after 4 October 1582 was adopted, it will be immediately 15 October. In this way, they reinstated the date of the equinox.
still remained to shorten some year. Therefore it is assumed that if the number of years in a given year divided by 100 (years ending centuries) it was the years of ordinary, although it shared divisible by 4. But if the number of years of shared divisible by 400 are leap years were . So 2000 was a leap year because the number is divisible by 400 was, but for 2100, although divisible by 4, it will be counted only 365 days. Complicated, but effective. Dr. Bednarek: – It gave us the length of the calendar year fairly well matched. Now the tropical year differs from the calendar year by 26 seconds. This again causes some shifts, but it will be visible after a much longer period of time.
(ew / pap)
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