- Khalid Ben Abdulmelik
Chalid Ben Abdulmelik al-Marwzi ( _ar. خالد بن عبدالملك) was a PersianFact|date=May 2007
astronomer of the9th century .Together with
Ali Ben Isa in827 , he measured at 35 degrees north geographicallatitude , in the valley of theTigris , thelength of a meridian and thus theEarth 'scircumference , getting a result of 40,248 km (or, according to other sources, 41,436 km). The two researchers measured in Arabianell , and determined the geographical latitudes of the end points they used from the star altitudes in a celestialhorizontal coordinate system . We believe that 1 Arabian ell was 49 1/3 cm. Thus, they found the length of 1° of meridian to be 111.8 km (115.1 km), which differs from the actual value by 850metre s.
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