Wednesday 19 March 2014

Which Calendar is More Accurate - The Pope's or Omar Khayyam's?

Every culture and region has its own calendar. Since the European Renaissance the modern world revolves around the Gregorian calendar but is there another calendar that is more accurate?

Accuracy of the Gregorian Calendar

The Gregorian calendar was created in 1582 based on the refinement of the Justinan calendar. The Justinian calendar was 11 minutes longer than the actual year (every 400 years the calendar was off by 3 days) and the Gregorian calendar set out to fix this “drift”.

The Gregorian calendar added a leap year ever 4 years except the centurial years which could be a leap year if it was divisible by 400. With this mathematical foot work, the European mathematicians created a calendar that was 10.8 seconds longer than the actual year (every 8000 years the Gregorian calendar would be off by 1 day).

But is there another calendar more accurate than the Gregorian calendar?

Omar Khayyam

Omar Khayyam was born in the year 1048 in Nishapur in modern day Iran. He was a mathematical and astronomical genius. He came from a poor family of tent makers but his mother recognized his talents for what they were and packed him off to learn from learned men.

During his lifetime, he would author a book on how to solve cubic equations which could only be understood by advance math students 1000 years later. His work in geometry would lead to the gradual development of non-Euclidean geometry and his work in astronomy would lead to his theory that the earth revolved around its axis rather than the planets orbiting around Earth.

Omar Khayyam had a brilliant mind.

Accuracy of Omar Khayyam's Calendar

In 1073 the Sultan of the Seljuk Empire Malik Shah asked Omar Khayyam to become the court mathematician and astronomer. The Sultan gave him the assignment of building an observatory and recalculating the calendar for accuracy.

For the next 6 years, Omar Khayyam and his team will observe the stars and plot the cosmos. In 1079 in an amazing feat of computation, Omar Khayyam calculated the length of the year to be 365.24219858156 days.  In the modern day with atomic clocks and super computers, scientists have calculated the length of the year to be 365.242190 days.  Omar Khayyam’s calculation is off by fractions of a second. The length of the year calculated by Omar Khayyam is only 0.741312 seconds longer than the actual year (every 116,550 years the calendar would be off by 1 day).

Omar Khayyam’s calendar would be adapted as the official calendar by the Empire and would be referred to as the Jalili calendar.

The Jalili calendar is still in use today in Iran and Afghanistan.

Note: In 1976, In recognition of the accomplishments of Omar Khayyam in the field of mathematics and astronomy, the Working Group for Planetary System Nomenclature (IAU/WGPSN) named moon crater 58.0N, 102.1W Omar Khayyam in his honor.

For the astronomers out there

Tropical year:                      365.242190 days (measured by the modern world)
Jalil Calendar:                     365.24219858156 days (Omar Khayyam)
Gregorian Calendar:             365.2425 days
Justinian Calendar:              365.245 days

-- End --


Morgan, Michael Hamilton. “Lost history – The Enduring Legacy of Muslim Scientists, Thinkers and Artists.” Washington D.C.: National Geographic Society 2007.

 “Gregorian calendar.” Wikipedia. March 15, 2014. March 16, 2014

“Leap Year.” Wikipedia. March 19, 2014. March 19, 2014

Reidel, D. “IAU Transactions XVIB.” The Moon Wiki. Nov 14, 2010. March 19, 2014 <>

“Tropical Year.” Wikipedia. February 19, 2014. March 17, 2014


  1. EXCELLENT!Open more on Islamic stuff n Allah(s.w) will reward you,InshaAllah.

  2. dear Naeem, am reading this for the first time. quite impressive
    thanks a lot for the article.
    my question for is why the hijri calendar is off by 10/11 days then??