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Is there a perfect calendar?

No calendar used today is perfect. They are off by seconds, minutes, hours or days every year, when compared to the tropical year, as per the table below.

Name of calendarWhen introducedAverage yearApproximate error introduced
Gregorian calendarAD 1582365.2425 days27 seconds (1 day every 3,236 years)
Julian calendar45 BC365.25 days11 minutes (1 day every 128 years)
365-day calendar-365 days6 hours (1 day every 4 years)
Lunar calendarancient12-13 moon-monthsvariable

The tropical year, also known as the solar year, is about 365.242199 days, but varies from year to year because of the influence of other planets. It is the time that the Earth takes to circle once around the sun.

A more accurate calendar

To make a calendar more accurate, new leap year rules were introduced to the Gregorian calendar, complicating the calendar’s calculations even more. The calendar will need some changes in a few thousand years.

What is a leap year and why is it used?
Leap Day — February 29
February 30 was a real date

Why the change from the Julian to the Gregorian calendar?

The Julian calendar introduced too many leap days, thus increasing the number of days between the March equinox, its scheduled date as noted in AD 325 during the Council of Nicaea. The introduction of the Gregorian calendar allowed for realignment with the equinox; however, a number of days had to be dropped when the change was made.

Leap Year in other calendars

In ancient times, it was customary to have lunar (moon) calendars, with 12 and/or 13 months every year. To align the calendar with the seasons, the 13th month was inserted as a "leap month" every 2 or 3 years. Many countries, especially in Asia still use such calendars.

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