Hulegu was very pleased with his conquest of Baghdad and also pleased that such an eminent scholar as al-Tusi had joined him. So, when al-Tusi presented Hulegu with plans for the construction of a fine Observatory, Hulegu was happy to agree. Hulegu had made Maragheh his capital . Maragheh was in the Azerbaijan region of northwestern Iran, and it was at Maragheh that the Observatory was to be built.
Hulegu ay lubhang nalulugod sa kaniyang pagsakop ng Baghdad at natutuwa din na tulad ng isang mataas iskolar bilang al-Tusi had sumali sa kanya. Kaya, kapag al-Tusi ipinapahayag Hulegu sa mga plano para sa pagbubuo ng isang mabuting obserbatoryo, Hulegu ay masaya na sumang-ayon. Hulegu had ginawa Maragheh kanyang kapital. Maragheh ay sa Azerbaijan rehiyon mula sa hilagang-kanluran ng Iran, at ito ay sa Maragheh na ang obserbatoryo ay binuo.