OMAR KHAYYAM

Astronomer


Like most mathematicians of the period, Omar Khayyám was also famous as an astronomer. In 1073, the Seljuk dynasty Sultan Sultan Jalal al-Din Malekshah Saljuqi (Malik-Shah I, 1072-92), invited Khayyám to build an observatory, along with various other distinguished scientists. Eventually, Khayyám and his colleagues measured the length of the solar year as 365.24219858156 days (correct to six decimal places). This calendric measurement has only an 1 hour error every 5,500 years, whereas the Gregorian Calendar, adopted in Europe four centuries later, has a 1 day error in every 3,330 years, but is easier to calculate.




Calendar Reform

Omar Khayyam was part of a panel that introduced several reforms to the Persian calendar, largely based on ideas from the Hindu calendar. On March 15, 1079, Sultan Malik Shah I accepted this corrected calendar as the official Persian calendar.

This calendar was known as Jalali calendar after the Sultan, and was in force across Greater Iran from the 11th to the 20th centuries. It is the basis of the Iranian calendar which is followed today in Iran and Afghanistan. While the Jalali calendar is more accurate than the Gregorian, it is based on actual solar transit, (similar to Hindu calendars), and requires an Ephemeris for calculating dates. The lengths of the months can vary between 29 and 32 days depending on the moment when the sun crossed into a new zodiacal area (an attribute common to most Hindu calendars). This meant however, that seasonal errors were lower than in the Gregorian calendar.

The modern day Iranian calendar standardizes the month lengths based on a reform from 1925, thus minimizing the effect of solar transits. Seasonal errors are somewhat higher than in the Jalali version, but leap years are calculated as before.

Omar Khayyám also built a star map (now lost), which was famous in the Persian and Islamic world.



Heliocentric Theory

It is said that Omar Khayyam also estimated and proved to an audience that included the then-prestigious and most respected scholar Imam Ghazali, that the universe is not moving around earth as was believed by all at that time. By constructing a revolving platform and simple arrangement of the star charts lit by candles around the circular walls of the room, he demonstrated that earth revolves on its axis, bringing into view different constellations throughout the night and day (completing a one-day cycle). He also elaborated that stars are stationary objects in space which if moving around earth would have been burnt to cinders due to their large mass. Some of these ideas may have been transmitted into the Christian science post Renaissance.

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