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Al‐Malik Al‐Ashraf (Mumahhid Al‐Din) Umar Ibn Yūsuf Ibn Umar Ibn Alī Ibn Rasul (Arabic: عمر بن يوسف بن عمر بن علي بن رسول الغساني), also as Umar Ibn Yusuf (or also Al-Asharaf Umar II) was the third Rasulid sultan and also an mathematician, astronomer and physician.

Umar Ibn Yussuf
Coin of the Rasulids in 1335.
Born	circa 1242 Yemen
Died	22 November 1296 Yemen
Scientific career
Fields	Astronomy, Mathematician and Physician

Biography

Umar Ibn Yusuf was born in 1242 in Yemen and he died in 1296. [2] He is known for writing the first description of the use of a magnetic compass for determining the qibla.[1] Also, his works on astronomy contain important information on earlier sources.[1]

In a treatise about astrolabes and sundials, al-Ashraf includes several paragraphs on the construction of a compass bowl (ṭāsa). He then uses the compass to determine the north point, the meridian (khaṭṭ niṣf al-nahār), and the Qibla towards Mecca. This is the first mention of a compass in a medieval Islamic scientific text and its earliest known use as a qibla indicator, although al-Ashraf did not claim to be the first to use it for this purpose.[1]

We owe him a famous astrolabe made in 1291, actually in the New York Metropolitan Museum of Art.[3]

Notes

References

• Schmidl, Petra G. (2007). "Ashraf: al‐Malik al‐Ashraf (Mumahhid al‐Dīn) ʿUmar ibn Yūsuf ibn ʿUmar ibn ʿAlī ibn Rasūl". In Thomas Hockey; et al. (eds.). The Biographical Encyclopedia of Astronomers. New York: Springer. pp. 66–7. ISBN 9780387310220. (PDF version)

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