| From: Thomas Hockey et al. (eds.). The Biographical Encyclopedia of Astronomers, Springer Reference. New York: Springer, 2007, pp. 66-67 |
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Ashraf: al‐Malik
al‐Ashraf (Mumahhid
al‐Dīn) ʿUmar ibn Yūsuf ibn ʿUmar ibn ʿAlī ibn Rasūl
Petra G. Schmidl
Born circa 1242
Died (Yemen), 22
November 1296
al‐Ashraf
ʿUmar, the
third of the Rasulid sultans in Yemen, was a prolific scholar who wrote a
number of works with astronomical content. The date of Ashraf's birth is uncertain,
and only a few details of his life are recorded. In 1266/1267, Ashraf commanded
a military mission for his father to the northern town of Ḥajja and
later became governor of al‐Mahjam along Wādī Surdud in the
coastal region of Yemen. His father, al‐Muẓaffar
Yūsuf, appointed him coregent in 1295. Four months later Ashraf ʿUmar
succeeded him on the throne. In the same year Malik al‐Ashraf visited
al‐Dumluwa and later the coastal town of Zabīd. He reigned in Yemen
for about 2 years until his death in 1296. He was buried in the Ashrafiyya
school he had founded in Taʿizz.
Ashraf left behind six sons and two daughters, both married to sons of Ashraf's
brother, Muʾayyad Dāwūd, who succeeded him on the throne.
In
contrast to his father's reign, which was long and prosperous, Ashraf's own
reign was short‐lived and without major historical significance. His
minor importance for the political history of his realm is counterbalanced
by his considerable contribution to science.
Ashraf
wrote some 13 treatises on a variety of scientific fields including medicine,
genealogy, agriculture, veterinary medicine, astronomy, and astrology. He
made several astronomical instruments, among which were astrolabes. For the
sake of brevity, only the extant contributions to astronomy will be mentioned.
In the
Metropolitan Museum of Art in New York, an Islamic astrolabe is preserved
that is signed by ʿUmar b. Yūsuf
b. ʿUmar b.
ʿAlī b. Rasūl
al‐Muẓaffarī,
i. e., Ashraf, dated 1291, and measures 15.5 cm in diameter. It is
competently made without being particularly sophisticated, but some unusual
features make it unique: on the rete, there is a scale for the lunar mansions;
and on the back, there is astrological information using planetary symbols
that had been adopted by Muslims from Greek sources. The plates are engraved
for latitudes in Yemen and Hejaz and were constructed using the tables presented
in Ashraf's treatise on the construction of the astrolabe, not by using geometrical
construction.
Ashraf's
treatise on the construction of the astrolabe as well as other instruments,
entitled Muʿīn
(or Minhaj) al‐ṭullāb fī al‐ʿamal
bi‐ʾl‐asṭurlāb,
is preserved in two manuscripts in Cairo and Tehran. The sultan mentions there
the extensive treatise on spherical astronomy and astronomical instruments
written by Marrākushī. Ashraf's
treatise contains an explanatory text on the construction of an astrolabe,
diagrams of the different parts, and tables for the construction of, for example,
the altitude circles and the azimuth circles for specific latitudes in Yemen
and the Hejaz, and tables of the shadows‐lengths and the altitude of
the Sun at the beginning of the afternoon prayer. The two star catalogs use
the degree of the ecliptic with which the star culminates and the radius of
the day circle of the star and not, as more usual, the ecliptic or equatorial
coordinates.
The
star pointers on the rete of Ashraf's astrolabe do not correspond with the
star positions mentioned in his treatise. Nevertheless, the connection between
instrument and text is definite. In particular, the back of the astrolabe
made by Ashraf, and the illustration of the back of an astrolabe in his treatise,
are virtually identical. It is indeed rare that we find references in the
medieval literature to specific instruments that have survived to this day.
In his treatise, Ashraf deals not only with the astrolabe but also
with horizontal sundials, the water clock, and the magnetic compass. At the
end, the text is supplemented with notes by two of Ashraf's teachers. The
section on the sundial contains tables of coordinates for marking the seasonal
hours on the shadow traces of the zodiacal signs computed for latitudes in
Yemen and the Hejaz, using 23° 30'
for the obliquity of the ecliptic. These tables are of the same kind as those
of Ḥabash and Marrākushī,
who use 23° 51'
and 23° 35', respectively. The section
on the magnetic compass describes the construction and use of a floating compass.
Ashraf
explains the making of the compass bowl, with the rim and the scales engraved
there, and the preparation of the magnetic needle, which is inserted crosswise
in a stalk. He continues with the determination of the meridian under bad
weather conditions, using the magnetic compass, and the use of this information
to find the qibla, the sacred direction of Islam to Mecca, which one
should know to fulfill several Islamic religious obligations such as the five
daily prayers. This is the first time the magnetic compass is mentioned in
a medieval astronomical treatise and also the first time that it is used as
a qibla‐indicator.
The
notes by two of his teachers inform us that they have inspected four or six
astrolabes, made by Ashraf himself, which are most accurate and skillful.
They testify to Ashraf's excellence in the construction of astrolabes and
give him permission to make whatever he likes in the way of astrolabes. Additionally,
they mention two water clocks made by Ashraf. So it is probable that Ashraf
also made other instruments, such as the sundials described in his treatise.
Ashraf's
third contribution to the science of the stars is his extensive collection
of astronomical texts and related subjects entitled Kitāb al‐Tabṣira
fī ʿilm
al‐nujūm, preserved in Oxford. It contains 50 chapters on astrology
and astronomy, timekeeping, and an almanac. In essence, it represents an introduction
to medieval astronomy that includes basic zodiacal and planetary astrology
as well as a range of information on timekeeping systems. The subjects covered
include the zodiac, the course of the Sun, the course of the Moon, planets,
fixed stars, eclipses, astrolabes, lunar mansions, calendar systems, determination
of the qibla, weather, medicinal regimes for each season, the agricultural
calendar, and systems of numbers. Most of the chapters deal with astrology,
but there are also lengthy chapters on timekeeping including tables displaying
the solar altitude and longitude of the horoscope as functions of the solar
longitude for each seasonal hour of the day. Another table gives the geographical
coordinates of different localities. The Tabṣira draws on a wide variety
of earlier texts and authors; among others, Dorotheus and Kūshyār
ibn Labbān are mentioned.
In
Chapter 32, Ashraf documented the seasonal reckoning of changes in nature
and human activities. This almanac is the earliest known treatise of this
kind written in prose about Yemen and was probably compiled in about 1271.
It is arranged in tabular form. Each page contains daily data for half of
the solar Christian month (beginning in October). Each bears information on
the entry of the Sun in each sign, the hours of daylight and darkness, and
the shadow‐lengths for the beginning of the midday and afternoon prayers
(for the beginning and midpoint of each month). For the anwāʾ
(certain stars used for weather prognostication), Ashraf relied upon Ibn Qutayba.
The information in the almanac derives both from the general almanac tradition
and from knowledge of local practices and folklore.
Ashraf
was not a great genius but a teachable pupil and a versatile scholar. His
astronomical treatises bear a great deal of information about earlier texts.
The uniqueness of his astronomical work is due in part to the vicissitudes
of history. It is Ashraf who, for the first time, documented in tabular form
the yearly astronomical and agricultural events in medieval Yemen. It is Ashraf's
description of the magnetic compass that, for the first time, proves that
the magnetic compass was used as a qibla‐indicator, though the
author makes no claim to have invented the device. And it is a real windfall
that one of the sultan's astrolabes and his treatise on the construction of
the astrolabe are preserved.
Selected References
King, David A. (1983).
Mathematical Astronomy in Medieval Yemen: A Biobibliographical
Survey. Malibu: Undena Publications. (On Ashraf in the context of Yemeni astronomy.)
(1985). The Medieval Yemeni Astrolabe
in the Metropolitan Museum of Art in New York City. Zeitschrift fόr die Geschichte
der Arabisch‐Islamischen Wissenschaften 2: 99122. (Reprinted in King, Islamic
Astronomical Instruments, II. London: Variorum
Reprints, 1987. Supplement in King, Zeitschrift
fόr die Geschichte der ArabischIslamischen Wissenschaften 4
(198788): 268269. (On Ashraf's
actual astrolabe and the treatise on its construction.)
Schmidl, Petra
G. (199697). Two Early Arabic Sources on the Magnetic Compass. Journal
of Arabic and Islamic Studies 1: 81132. (On the magnetic
compass.)
Varisco, Daniel
Martin (1994). Medieval Agriculture and Islamic Science: The Almanac of
a Yemeni Sultan. Seattle: University of Washington Press. (On Ashraf's almanac.)