Yaÿqà «b ibn ṬÃÂriq (; referred to by some sources as Yaÿqà «b; died ) was a Persian astronomer and mathematician who lived in Baghdad.
Yaÿqà «b ibn ṬÃÂriq was active in Baghdad as an astronomer during the rule of the second Abbasid caliph, al-Maná¹£à «r (). He seems not to have been aware of Ptolemaic astronomy, and used a Zoroastrian calendar, which consisted of 12 months of 30 days each, with any remaining days being added after the eighth month, ÃÂbÃÂn.
Yaÿqà «b ibn ṬÃÂriq's treatise dealt with cosmography (the placement and sizes of the heavenly bodies). The estimations of their sizes and distances in were tabulated in the 11th century by the polymath al-Bërà «në, in his work on India. According to al-Bërà «në, Yaÿqà «b ibn ṬÃÂriq gave the radius of the Earth as 1,050 , the diameter of the Moon and Mercury as 5,000 (4.8 Earth radii), and the diameter of the other heavenly bodies (Venus, the Sun, Mars, Jupiter, and Saturn) as 20,000 (19.0 Earth radii). He wrote that each of the planets had six associated spheres, that the Sun possessed two spheres, and the Moon three.àHe also spoke of planetary epicycles and speeds. His values for the longitudes and apogees of celestial objects originated from a Persianàset of astronomical tables, the written by Yazdegerd III, although he used methods originating from the work of Indian astronomers to calculate the lunar phases.
The Christian astrologer Ibn Hibintàmentioned Yaÿqà «b, noting that he used the positions of the Sun and the stars to determine the latitude of places.
Works ascribed to Yaÿqà «b ibn ṬÃÂriq include:
An astrological work, ("The Chapters"), is ascribed to Yaÿqà «b ibn ṬÃÂriq by an unreliable source.
Yaÿqà «b ibn ṬÃÂriq's zij, written in around 770, was based on a Sanskrit work, thought to be similar to the BrÃÂhmasphuá¹ÂasiddhÃÂnta. It was brought to the court of al-Mansà «r, the third caliph of the Fatimid Caliphate, from Sindh, reportedly by the Sindhi astronomer Kankah.