  Khayyam moved to Isfahan in 1074 to help establish a new observatory under the patronage of Malikshah, the Seljuk sultan, and his vizier, Nizam al-Mulk. There is little doubt that Khayyam played a major role in the creation of the Malikī calendar, the observatory’s most significant project. In addition to the calendar, the Isfahan observatory produced the Zīj Malikshah (of which only a fragment of its star catalogue survives); it seems to have been one of the more important astronomical handbooks.