Who created the Gregorian calendar

The Gregorian calendar

The Gregorian calendar is the internationally recognized calendar system, which is often referred to as the “Western Calendar” or “Christian Calendar”. It was named after the Pope who introduced it in February 1582: Gregory XIII.

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The Gregorian calendar is a solar calendar (or solar calendar). This means that - in contrast to lunar calendars (or lunar calendars) - it relates to the course of the earth around the sun. It consists of 365-day common years, which in turn are divided into 12 months of different lengths. Most months have 30 or 31 days, with a month (February) in the common year only having 28 days. Every four years, a leap year is inserted in which February is 29 days long - the leap year has 366 days.

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Adjustment to the solar year

The Gregorian calendar was not a completely new calendar system when it was first introduced. Rather, it is a further development of the Julian calendar. This was abolished because, although it was a solar calendar, it did not exactly reflect the exact length of a solar year. Every 128 years there was a deviation of one day. The Julian calendar was therefore unusable for long periods of time.

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The Gregorian calendar, on the other hand, was based much more precisely on the exact length of the solar year - in other words, on the period between two equinoxes. Since the incorrect time calculation of the Julian calendar had accumulated a discrepancy between astronomical time and calendar over the centuries, this had to be compensated for when the Gregorian calendar was introduced. A few days were skipped - see about October 1582 in Italy.

However, the Gregorian calendar is not entirely perfect either: its error rate is one day in 3236 years.

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From the Julian to the Gregorian calendar

The calendar reform brought the following changes:

  • A few days were skipped when the new calendar system was introduced. Where the transition occurred in 1582, 10 days were left out. The later the Gregorian calendar was introduced, the more days were missing from the calendar.
  • New rules for determining the Easter date have been introduced.
  • The rules for determining leap years have been changed. In the Julian calendar, every fourth year was a leap year. A leap year in the Gregorian calendar must meet the following requirements:
    1. The year must be completely divisible by 4;
    2. The year must not be completely divisible by 100;
    3. If a year number that is completely divisible by 100 is also completely divisible by 400, the year is still a leap year.

Thus the years 1900, 2100 and 2200 are not leap years. However, the years 1600, 2000 and 2400 are leap years.

The time calculation of the Julian calendar is currently (in the period from 1901 to 2099) 13 days behind that of the Gregorian calendar. For this reason, for example, the Christian Orthodox churches, which still use the Julian calendar to calculate their holidays, celebrate New Year 13 days later than the Western churches, which use the Gregorian calendar to determine the date of their holidays.

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Worldwide introduction of the Gregorian calendar

The Gregorian calendar was first introduced in Italy, Poland, Portugal, and Spain in 1582. In Great Britain and in what is now the USA, the reform did not come until September 1752. Eleven days were canceled, with September 2 followed by September 14.

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From today's perspective, the consequences of the calendar reform in Sweden and Finland were also curious. There was a "double" leap year in 1712, February not only had 29 but 30 days. The reason for this probably unique process: The year 1700 was wrongly not defined as a leap year there, so that a day had to be made up in order to match the Julian calendar again.

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Subjects: History, calendar, calendar