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  • Writer's pictureMohammed M Masood

When the Calendar Jumped Days - A brief narrative of the Gregorian Calendar

© 2021 Mohammed M Masood

Earlier this month many of us celebrated and wished each other ‘Happy New Year’. It was the start of the year 2021. However not many are aware that this calendar currently followed by majority of the people and countries in the world was introduced by Pope Gregory X111 in the year 1582 as a modification to the Julian Calendar which was also known as the Old Style Calendar. Therefore, our current calendar is known as the Gregorian Calendar also called the New Style Calendar. Not just that, it was him who made January 1st again the start of the new year changing it from March 25th which was the the day of Annunciation and also the start of the New Year. 1

Both Julian and Gregory calendars are Solar Calendars i.e. the year is based on the time taken by the Earth to make one round of the Sun. The Julian Calendar calculated this time to be 365 days and a quarter day (6hrs) precisely whereas the Gregorian Calendar sees it more accurately as 11 minutes and 45 seconds shorter to 365 ¼ days.

Both the Julian Calendar and the Gregorian Calendar had leap years to make adjustment for the quarter day however the rule with Julian Calendar was that there would be a leap year every 4 years – the same as in the Gregorian Calendar but with the Gregorian Calendar the Centennial years would not have a leap year unless they were also divisible by 400. So where every centennial year like 1100, 1200, 1300,1400, 2100, etc would be a leap year under the Old Style calendar as these would be divisible by 4 - only years such as 1600, 2000 and next 2400 would have a leap year under the New Style calendar as these centennial years are divisible by both 4 and 400. 2

So what prompted the Pope to bring about this change and how did this small error in calculation make a difference? One must remember that solar calendars are primarily used as seasonal calendars by people where different months present different seasons and people use them to plan their various activities – work, agriculture, tax, vacations, etc. Similarly, certain festivals don’t have fixed dates – unlike Christmas which has a fixed date of 25th December every year – the Easter festival date in Christianity occurs on the first Sunday after the full moon after the spring equinox – i.e. when the Sun passes the Equator and moves from the Southern to the Northern Hemisphere. Traditionally and as per the Church traditions March 21st is the date used to calculate the date of Easter every year – the Sunday falling after first full moon on or after 21st March ( the ecclesiastical or Church determined date for the equinox) would be the Easter Sunday. However, with the Julian Calendar the spring equinox was occurring before this date of 21st March. 3

Vernal Equinox is also known as Spring Equinox. Image used for illustration.

Therefore, the Pope constituted a commission to look into this problem and they came up with this calendar after almost 5 years of being set up which was ratified by the Pope through a papal decree in 1582. Thereafter, in October of that year the date after October 4, 1582 (Julian calendar) was October 15, 1582 (Gregorian calendar) - there was a jump of 10 days to sync it with astronomical events . The calendar had changed and it was quickly adopted by Catholic Europe – Italy, Spain, Portugal, Poland, etc and their colonies. However, Protestant and Eastern Orthodox countries were initially skeptical as can be seen with England and its colonies who adopted this ‘New Style Calendar only in 1752 when it had to skip 11 days to align itself to the date of the Gregorian Calendar. 4

Calendar of the United States when it move to the Gregorian Calendar. US was still a colony at the time of this change.

This is a short snippet of our calendar history that we use today. However an important assertion that I would like to make is that students of history need to be careful when they look for dates in the past as I came to realize this when one of my good friends asked me to look for a corresponding date (Battle of Talikota - 1565) in the Hijri Calendar. When looking for this I found there to be a mismatch with the day and soon realized that lot of dates that were recorded especially by contemporary historians and which are now copied even by modern historians are actually based on the Julian Calendar. This prompted me to pen this article.

Here are a few links which can be used for conversion of dates between different calendars - Gregorian, Julian, Hijri, Persian, Hebrew, etc

© 2021 Mohammed M Masood

Notes & References:

  1. Definitions of Our Year? <> (accessed on 22nd Jan 2021)

  2. Carol McPhail, Who moves Easter? Blame the moon, the early church and Pope Gregory X111 <> (accessed on 22nd Jan 2021)

  3. Richard Bevan, The Calendar Riots of 1752: When Britain lost 11 Days. <> (accessed on 22nd Jan 2021)


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