Page 73 - Arabian Studies (V)

Mathematical Astronomy in Medieval Yemen 63
Iraqi and Egypt ztj handbooks. The Sultan al-Ashraf himself
compiled an extensive treatise on the construction of astrolabes and
sundials, displaying his knowledge of certain earlier Andalusian
and Egyptian works on these instruments. He compiled new tables
of coordinates for drawing the curves on astrolabe plates and the
curves on horizontal sundials, computing these tables for the
latitudes of the major cultural centres of the Yemen and the Hejaz.
One of the astrolabes made by al-Ashraf with the aid of these tables
is now preserved in the Metropolitan Museum of Art in New York.
However, perhaps the most interesting feature of al-Ashraf’s
treatise is that it contains as an appendix a discussion of the
magnetic compass: this is the earliest known reference to the
compass in an Arabic astronomical text. Al-Ashraf also compiled
an extensive treatise on astrology, in which he included astrological
tables specifically computed for the latitude of San‘a\
The Yemeni astronomer Abu ’l-‘Uqul worked for the Sultan al-
Mu’ayyad. He compiled a ztj based on one of the ztj handbooks of
the celebrated tenth century Cairo astronomer Ibn Yunus, and
included tables specifically computed for the latitudes of Aden,
Ta‘izz, Zabld, and San‘a\ Some of the material lifted by Abu
’l-‘Uqul from Ibn Yunus is not extant in any of the manuscripts of
Ibn Yunus’ own works.6 Greater originality is displayed in the
corpus of tables for timekeeping attributed to Abu ’l-‘Uqul. These
tables for timekeeping by the sun and stars, computed for the
latitude of Ta‘izz, constitute the largest known corpus of such
tables compiled for any Islamic city during the medieval period,
being considerably more extensive than the corresponding tables
that were prepared in the thirteenth and fourteenth centuries for
such centres of astronomy as Cairo and Damascus. In fact, the
Ta'izz, corpus contains over one hundred thousand entries, but it is
difficult to estimate the extent to which these tables were used in
later centuries since they survive in only two manuscripts whereas
literally dozens of manuscripts of the Cairo and Damascus tables
survive. No comparable corpus of tables for timekeeping appears
to have been compiled for San‘a’.
Each year almanacs and ephemerides were prepared for the
Yemeni Sultans by their astronomers. These contained extensive
calendrical and astrological information for the year in question, as
well as tables of the positions of the sun, moon, and planets for
each day of the year. Two of these survive in the manuscript
sources: the first was prepared for San‘a’ in 727 Hijrah (3 1326/7),
and the second for Ta‘izz in 808 Hijrah (= 1405/06).
The Sultan al-Afdal compiled an extensive compendium of astro­
nomical treatises and tables, most of which were simpy lifted from