As an astronomer, he designed the Jalali calendar, a solar calendar with a very precise 33-year intercalation cycle  that provided the basis for the Persian calendar that is still in use after nearly a millennium. In the 1000s in Persia, Khayyam announced in 1079, that the length of the year was measured as 365.24219858156 days. Given that the length of the year is changing in the sixth decimal place over a person's lifetime, this is outstandingly accurate. For comparison the length of the year at the end of the 19th century was 365.242196 days, while today it is 365.242190 days.   The Moving Finger quatrain A line of English translation of the Persian poetry of Omar Khayyam on one of the faculty buildings of Leiden University A line of English translation of ''The Moving Finger'' quatrain. Persian Rubiyats of Omar Khayyam on one the faculty buildings of Leiden University The quatrain by Omar Khayyam known as "The Moving Finger", in the form of its translation by the English poet Edward Fitzgerald is one of the most popular quatrains in the Anglosphere. It reads:   The Moving Finger writes; and having writ,  Moves on: nor all your Piety nor Wit  Shall lure it back to cancel half a Line,  Nor all your Tears wash out a Word of it.   There is a tradition of attributing poetry to Omar Khayyam, written in the form of quatrains (rubāʿiyāt رباعیات). This poetry became widely known to the English-reading world in a translation by Edward FitzGerald (Rubaiyat of Omar Khayyam, 1859), which enjoyed great success in the Orientalism of the fin de siècle.