Al‐Malik Al‐Ashraf (Mumahhid Al‐Din) Umar Ibn Yūsuf Ibn Umar Ibn Alī Ibn Rasul (), also as Umar Ibn Yusuf (or also Al-Asharaf Umar II) was the third

Rasulid The Rasulids ( ar, بنو رسول, Banū Rasūl) were a Sunni Muslim dynasty who ruled Yemen from 1229 to 1454. History Origin of the Rasulids The Rasulids took their name from al-Amin's nickname "Rasul". The Zaidi Shi'i Imams of Yemen we ...

sultan and also an

mathematician A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems. Mathematicians are concerned with numbers, data, quantity, structure, space, models, and change. History On ...

astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either ...

and physician.

Biography

Umar Ibn Yusuf was born in 1242 in Yemen and he died in 1296. He is known for writing the first description of the use of a

magnetic compass A compass is a device that shows the cardinal directions used for navigation and geographic orientation. It commonly consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with ...

for determining the

qibla The qibla ( ar, قِبْلَة, links=no, lit=direction, translit=qiblah) is the direction towards the Kaaba in the Sacred Mosque in Mecca, which is used by Muslims in various religious contexts, particularly the direction of prayer for the ...

. Also, his works on astronomy contain important information on earlier sources. In a treatise about

astrolabes An astrolabe ( grc, ἀστρολάβος ; ar, ٱلأَسْطُرلاب ; persian, ستاره‌یاب ) is an ancient astronomical instrument that was a handheld model of the universe. Its various functions also make it an elaborate inclin ...

and

sundials A sundial is a horological device that tells the time of day (referred to as civil time in modern usage) when direct sunlight shines by the apparent position of the Sun in the sky. In the narrowest sense of the word, it consists of a flat ...

, 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 Meridian or a meridian line (from Latin ''meridies'' via Old French ''meridiane'', meaning “midday”) may refer to Science * Meridian (astronomy), imaginary circle in a plane perpendicular to the planes of the celestial equator and horizon * ...

(khaṭṭ niṣf al-nahār), and the Qibla towards

Mecca Mecca (; officially Makkah al-Mukarramah, commonly shortened to Makkah ()) is a city and administrative center of the Mecca Province of Saudi Arabia, and the holiest city in Islam. It is inland from Jeddah on the Red Sea, in a narrow ...

. 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. http://www.uib.no/jais/v001ht/01-081-132schmidl1.htm#_ftn4 We owe him a famous astrolabe made in 1291, actually in the New York

Metropolitan Museum of Art The Metropolitan Museum of Art of New York City, colloquially "the Met", is the largest art museum in the Americas. Its permanent collection contains over two million works, divided among 17 curatorial departments. The main building at 1000 ...

.MET picture
— Sharon Kinoshita ''The Painter, the Warrior, and the Sultan: The World of Marco Polo in hree Portraits'', The Medieval Globe, vol. 2, n° 1, 2016, p. 120 sq.

Notes

References

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1242 births 1296 deaths 13th-century Arabs 13th-century astronomers Astronomers of the medieval Islamic world Yemeni astronomers Rulers of Yemen 13th-century rulers in Asia Rasulid dynasty {{Astronomer-stub