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Ali ibn Isa al-Asturlabi
ʿAlī ibn ʿĪsā
al-Asṭurlābī
was an
Arab
astronomer
and
geographer
of the
9th century
. He wrote a
treatise
on the
astrolabe
and was an
opponent
of
astrology
. During the
reign
of
al-Ma'mun
, and together with
Khālid ibn ʿAbd al‐Malik al‐Marwarrūdhī
, he participated in an
expedition
to the
Plain of Sinjar
to
measure
the length
of a
degree
, or the
circumference of the Earth
. He
measured
the
Earth's circumference
,
getting
a result of 40,248
km
.
