Interesting Facts About Calendar That We All Must Know

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  • According to Gregorian calendar, 1st January is the New Year. 
  • Before the Gregorian calendar’s adoption, the English new year began on March 25, or Lady Day. 
  • Gregorian calendar introduced by Pope Gregory XIII in 1582.
  • It is named after Pope Gregory XIII, who introduced this calendar. 
  • This calendar is also called the "Christian calendar" or "Western calendar.” 
  • It is internationally accepted as a civil calendar by most of the countries (almost all). 
  • 10 days were omitted from the Julian calendar (October 1582), So Julian October 4, 1582 was officially followed by Gregorian October 15, 1582.

Why

A year on the earth is the orbital period of the Earth moving  in its orbit around the Sun. It is also called tropical, solar year or astronomical year. It is approximately 365.24219 days long on average. 

The length of year in Julian calendar was 365.25 (each year has 365 days, except for a leap year every 4 years which has 366 days). It is inaccurate as per tropical year. Specifically the average year was slightly longer than it should have been (365.24219).

365.25 – 365.24219 = 0.00781 days, 
0.00781 * 24 * 60 = 11.2464 minutes 

Julian calendar was miscalculated the length of the Solar year by 11.2464 minutes. This results in an increase of one day every 128 years. After many centuries, Julian calendar became inaccurate to calculate the most important days like Christians festivals and exact seasons. 

To reform this Julian calendar, Gregorian calendar was introduced by Pope Gregory XIII in 1582. 

Leap Year in Gregorian Calendar: 

Every four years (Year is exactly divisible by four). Except for years exactly divisible by 100. But, years exactly divisible by 400 are leap years. For example, the years 1700, 1800, and 1900, 2100 are not leap years, but the year 2000 and 2400 is.

A mean Gregorian Calendar is 365 + 1/4 - 1/100 + 1/400 = 365.2425 days (365 days, 5 hours, 49 minutes and 12 seconds).

365.2425 - 365.24219 = 0.00031 days 
0.00031 * 24 * 60 * 60 = 26.784 seconds

The Gregorian calendar differs from the Solar year by 26.784 seconds per year. So it is off by one day every 3236 years.

Finally, the calendar what we are using also have error.



Reference

1. Gregorian calendar

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