Abdal Ali ibn Muhammad ibn Husayn Birjandi (Persian: عبدالعلی محمد بن حسین بیرجندی) (died 1528) was a prominent 16th-century Persian astronomer, mathematician and physicist who lived in Birjand.

[1] In discussing the structure of the cosmos, al-Birjandi continued Ali al-Qushji's debate on the Earth's rotation.

[2][3][4] In his analysis of what might occur if the Earth were moving, he develops a hypothesis similar to Galileo Galilei's notion of "circular inertia",[5] which he described in the following observational test (as a response to one of Qutb al-Din al-Shirazi's arguments): The small or large rock will fall to the Earth along the path of a line that is perpendicular to the plane (sath) of the horizon; this is witnessed by experience (tajriba).

And this perpendicular is away from the tangent point of the Earth's sphere and the plane of the perceived (hissi) horizon.

[6]Al-Birjandi wrote some more than 13 books and treatises, including:[7] Birjandi contributed to many different fields besides his commentaries.