Template:Are You Sure/February 18

• ... that polymath Thābit ibn Qurra Thabit rejected the Peripatetic and Aristotelian notions of a "natural place" for each element, and that Thābit instead proposed a theory of motion in which both the upward and downward motions are caused by weight, with the order of the universe a result of two competing attractions (jadhb): one of these being "between the sublunar and celestial elements", and the other being "between all parts of each element separately"?

• ... polymath Nasir al-Din al-Tusi convinced Hulegu Khan to construct an observatory for establishing accurate astronomical tables for better astrological predictions; that construction of the Rasad Khaneh observatory began in 1259; and that the observatory is located south of the river Aras, and to the west of Maragheh, the capital of the Ilkhanate Empire, in what is now Azarbaijan?