In the Eurasian world the astronomical observatory was an Islamic creation. Until Tycho Brahe founded his observatory at Uraniborg in 1576, fabricating astronomical instruments, carrying out a programme of observations, creating mathematical formulas and methods of computation, and composing astronomical works were all done in the Islamic world rather than in the European world. Although the first observatory with a sizeable number of large instruments and an extended programme of observation was that of the Seljuq ruler Malik Shah in Isfahan, there had been observation posts and smaller-scale observatories in the preceding centuries.

The earliest systematic observation programme in the Islamic world was conducted during the reign of the Abbasid caliph al-Ma'mun. This is not surprising for, as we have seen, he had established the House of Wisdom for the express purpose of translating into Arabic the works of the Indian and Greek scientists and philosophers. The Almagest and Handy Tables of Ptolemy were the most important of these works, and al-Ma'mun was interested in updating Ptolemy – primarily for astrological reasons, to more accurately determine the positions of the heavenly bodies. As a result, al-Ma'mun organised observations at two places – at Shammasiyya, a residential quarter within the city of Baghdad, in 828–9, and at Mt Qasiyun, in the vicinity of Damascus, in 831–2. The usual collection of small, mostly portable instruments was employed – armillary sphere, mural quadrant (see Glossary), gnomon (about sixteen feet tall), and azimuthal quadrant.

Because of the brief period devoted to observation, al-Ma'mun's results were limited. Yahya ibn Abi Mansur (d. 830), the caliph's senior astronomer, supervised the Baghdad programme and wrote the astronomical treatise that resulted – The Well-Tested Astronomical Treatise. Yahya's father, Abu Mansur Aban, had been an astrologer at the court of al-Mansur, and Yahya followed in his father's footsteps, becoming the personal astrologer and boon companion of the caliph and an important figure in the House of Wisdom. Although the corrections of Ptolemy in Yahya's treatise were few in number, they were not trivial. Most of the observations were of the Sun and Moon, and al-Ma'mun's astronomers calculated solar and lunar eclipses and arrived at a more accurate figure for the obliquity of the ecliptic – 23 degrees 33 minutes, more accurate than Ptolemy's 23 degrees 51 minutes.