Gregory Choniades (also Choniates, Chioniades; Greek: Γρηγόριος Χιονιάδης; c. 1240 – 1320) was a Byzantine Greek astronomer. He travelled to Persia where he learnt Persian mathematical and astronomical science which he introduced into Byzantium upon return from Persia and founded an astronomical academy at Trebizond. Choniades also served as Orthodox Bishop in Tabriz.
Information about Choniades survives from some contemporary sources. In 1347, George Chrysokokkes writes that "a certain Chioniades, who had been raised in Constantinople, fell in love with mathematics and other sciences. After he had mastered medicine, he wished to study astronomy; he was informed that, in order to satisfy his desire, he would have to go to Persia. He traveled to Trebizond, where he was given some assistance by the Emperor Alexios II of Trebizond, and thence proceeded to Persia itself, where he persuaded yet another Emperor to aid him. He eventually learned all that he wished to know, and returned to Trebizond, bearing away from Persia a number of astronomical texts which he translated into Greek."
Sixteen of Choniades' letters have survived, which confirm that he received assistance from Alexios II and traveled to Persia. Choniades translated a number of Arabic and Persian works on mathematics and astronomy, including the astronomical tables of his teacher Ajall Shams al-Din Omar, who had worked at the famous Maragheh observatory under the polymath Nasir al-Din al-Tusi. Choniades played an important role in transmitting several innovations from the Islamic world to Europe. These include the introduction of the universal latitude-independent astrolabe to Europe and a Greek description of the Tusi-couple, which would later have an influence on Copernican heliocentrism. Choniades also translated several Zij treatises into Greek, including the Persian Zij-i Ilkhani by al-Tusi and the Maragheh observatory  as well as the Seljuk Sanjaric Tables by Al-Khazini, an Islamic astronomer of Byzantine Greek descent.
Choniades resided in Tabriz, at the time the Mongol capital, from 1295 to 1296, serving as the Orthodox Bishop to the Orthodox living in that city and returned to Constantinople. In 1302 he returned to Tabriz as Bishop. According to David Pingree, this may have been in connection with Andronikos II Palaiologos's attempt to form an alliance with Ghazan Khan in the summer of 1302.
He died at Trebizond, probably in the second decade of the fourteenth century.
- Chioniades, Gregor [George]
- Nicholas J. Moutafakis, Byzantine Philosophy, Hackett Publishing, 2003, ISBN 0-87220-563-0, p. 200
- Zehiroğlu, A.M. "Astronomy in the Trebizond Empire", (2016), pp. 2-5
- David Pingree (1964), "Gregory Chioniades and Palaeologan Astronomy", Dumbarton Oaks Papers 18, p. 141
- Thomas Hockey at al. "Biographical Encyclopedia of astronomers".
- Joseph Leichter (June 27, 2009). "The Zij as-Sanjari of Gregory Chioniades". Internet Archive. Retrieved 2009-10-02.
- Pingree, "Gregory Chioniades", pp. 135-160.
- Fryde, Edmund Boleslaw "The Early Palaeologan Renaissance 1261 - C. 1360" 2000
- Westerink L. G. "La profession de foi de Grégoire Chioniadès", Revue des études byzantines, 38 (1980), pp. 233–245. Persee website
- Zehiroğlu, A.M. "Astronomy in the Trebizond Empire", (2016)
- Leichter, Joseph (student of David Pingree)."The Zij as-Sanjari of Gregory Chioniades: Text, Translation and Greek to Arabic Glossary".
- Haramundanis, Katherine (2007). "Chioniades, Gregor [George]". In Thomas Hockey; et al. The Biographical Encyclopedia of Astronomers. New York: Springer. p. 229. ISBN 978-0-387-31022-0. (PDF version)