Jalali Calendar Inaugurated at Isfahan

March 15, 1079

On the fifteenth of March, Omar Khayyam presented the completed Jalali calendar to Sultan Malik Shah. Five years of nightly observations had yielded a solar year measurement of 365.24219858156 days - accurate to the sixth decimal place, more precise than the Gregorian calendar that would arrive five centuries later. The calendar was immediately adopted across the Seljuk domains; variants of it remain in official use in Iran and Afghanistan to this day.