Ya'qub ibn Tariq

{{Infobox academic

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| name = Yaʿqūb ibn Ṭāriq

| native_name = یعقوب ابن طارق

| native_name_lang = ar

| birth_date = fl. 8th century

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| death_date = {{c.|796}}

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| era = Islamic Golden Age

| school_tradition =

| main_interests = Astronomer and mathematician

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Yaʿqūb ibn Ṭāriq ({{langx|fa|یعقوب ابن طارق}}; referred to by some sources as Yaʿqūb; {{sfn|Sezgin|2021|p=125}} died {{c.|796}}) was a Persian astronomer and mathematician who lived in Baghdad.

Career

File:Baghdad 150 to 300 AH.png's depiction of the original round city of Baghdad (1883), where Yaʿqūb ibn Ṭāriq was active during his career]]

Yaʿqūb ibn Ṭāriq was active in Baghdad as an astronomer during the rule of the second Abbasid caliph, al-Manṣūr ({{reign|754|775}}).{{sfn|Sezgin|2021|p=124}}{{cite web |last1=Hawting |first1=G.R. |title=al-Manṣūr |url=https://www.britannica.com/biography/al-Mansur-Abbasid-caliph |website=Britannica Online |access-date=8 May 2023}} He seems not to have been aware of Ptolemaic astronomy,{{sfn|Sezgin|2021|p=124}} and used a Zoroastrian calendar, which consisted of 12 months of 30 days each, with any remaining days being added after the eighth month, Ābān.{{sfn|Sezgin|2021|p=124}}

Yaʿqūb ibn Ṭāriq's treatise {{transliteration|ar|Tarkīb al‐aflāk}} dealt with cosmography (the placement and sizes of the heavenly bodies).{{sfn|Plofker|2007|pp=1250{{ndash}}1251}} The estimations of their sizes and distances in {{transliteration|ar|Tarkīb al‐aflāk}} were tabulated in the 11th century by the polymath al-Bīrūnī, in his work on India. According to al-Bīrūnī, Yaʿqūb ibn Ṭāriq gave the radius of the Earth as 1,050 {{transliteration|ar|farsakhs}}, the diameter of the Moon and Mercury as 5,000 {{transliteration|ar|farsakhs}} (4.8 Earth radii), and the diameter of the other heavenly bodies (Venus, the Sun, Mars, Jupiter, and Saturn) as 20,000 {{transliteration|ar|farsakhs}} (19.0 Earth radii).{{sfn|Pingree|1976|pp=106{{ndash}}107}} He wrote that each of the planets had six associated spheres, that the Sun possessed two spheres, and the Moon three. He also spoke of planetary epicycles and speeds.{{sfn|Sezgin|2021|p=126}} His values for the longitudes and apogees of celestial objects originated from a Persian set of astronomical tables, the {{transliteration|fa|Zīǧ aš-šāh}} written by Yazdegerd III, although he used methods originating from the work of Indian astronomers to calculate the lunar phases.{{sfn|Sezgin|2021|p=125}}

The Christian astrologer Ibn Hibintā mentioned Yaʿqūb, noting that he used the positions of the Sun and the stars to determine the latitude of places.{{sfn|Sezgin|2021|p=127}}

Works

Works ascribed to Yaʿqūb ibn Ṭāriq include:{{sfn|Plofker|2007|pp=1250{{ndash}}1251}}

{{transliteration|ar|Zīj maḥlūl fī al‐Sindhind li‐daraja daraja}} ("Astronomical Tables in the 'Sindhind' Resolved for each Degree");
{{transliteration|ar|Tarkīb al‐aflāk}} ("Arrangement of the Orbs"). Part of this work, the earliest surviving description of the celestial sky by an Islamic astronomer, is preserved by Ibn Hibintā.{{sfn|Sezgin|2021||pp=126{{ndash}}127}}
{{transliteration|ar|Kitāb al‐ʿilal}} ("Rationales");
{{transliteration|ar|Taqṭīʿ kardajāt al‐jayb}} ("Distribution of the {{transliteration|ar|Kardajas}} of the Sine");
{{transliteration|ar|Mā irtafaʿa min qaws niṣf al‐nahār}} ("Elevation along the Arc of the Meridian").

An astrological work, {{transliteration|ar|Al‐maqālāt}} ("The Chapters"), is ascribed to Yaʿqūb ibn Ṭāriq by an unreliable source.{{sfn|Plofker|2007|pp=1250{{ndash}}1251}}

Yaʿqūb ibn Ṭāriq's zij, written in around 770, was based on a Sanskrit work,{{sfn|Plofker|2007|pp=1250{{ndash}}1251}} thought to be similar to the Brāhmasphuṭasiddhānta. It was brought to the court of al-Mansūr, the third caliph of the Fatimid Caliphate, from Sindh,{{sfn|Pingree|1976|p=97}} reportedly by the Sindhi astronomer Kankah.{{sfn|Kennedy|1956|p=12}}

References

Sources

{{cite journal |last1=Kennedy |first1=Edward Stewart |author1-link=Edward Stewart Kennedy |title=A Survey of Islamic Astronomical Tables |journal=Transactions of the American Philosophical Society |date=1956 |volume=46 |issue=2 |pages= 123–177|doi=10.2307/1005726 |url=https://books.google.com/books?id=EywLAAAAIAAJ |series=New Series |publisher=American Philosophical Society |location=Philadelphia, Pennsylvania |jstor=1005726 |hdl=2027/mdp.39076006359272 |format=|via=|issn=0065-9746 |hdl-access=free }}
{{cite encyclopedia

| last = Pingree

| first = David

| title = Yaʿqūb ibn Ṭāriq

| encyclopedia = Dictionary of Scientific Biography

| volume = 14

| pages =

| editor = Gillispie, Charles Coulston

| publisher = Charles Scribner's Sons

| location = New York

| date = 1976

| isbn = 978-0-684-16962-0

| url = http://www.encyclopedia.com/doc/1G2-2830904745.html

}}

{{cite encyclopedia |editor=Thomas Hockey |display-editors=etal |last=Plofker |first=Kim |title=Yaʿqūb ibn Ṭāriq |encyclopedia=The Biographical Encyclopedia of Astronomers |publisher=Springer |date=2007 |author-link=Kim Plofker |location=New York |url=http://islamsci.mcgill.ca/RASI/BEA/Yaqub_ibn_Tariq_BEA.htm |isbn=978-0-387-31022-0}} ([http://islamsci.mcgill.ca/RASI/BEA/Yaqub_ibn_Tariq_BEA.pdf PDF version])
{{cite journal |last1=Sezgin |first1=Fuat |author1-link=Fuat Sezgin |title=III. Arab Astronomers |url=http://dx.doi.org/10.1163/2667-3975_SEZO_COM_603 |website=Sezgin Online |access-date=8 May 2023 |date=2021|doi=10.1163/2667-3975_SEZO_COM_603 |url-access=subscription }}

Ya'qub ibn Tariq

Career

Works

References

Sources

Further reading