Khalid ibn Abd al-Malik al-Marwarrudhi
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Khālid ibn ʿAbd al‐Malik al‐Marwarrūdhī (Template:Langx) was a 9th-century Baghdadi astronomer.Template:Sfn
In 827, Marwarrūdhī, together with the astronomer ʿAlī ibn ʿĪsā al-Asṭurlābī and a party of surveyors, measured the length of a meridian arc of one degree of latitude. The party travelled to the Nineveh Plains in the valley of the Tigris,Template:Sfn at 35 degrees north latitude.Template:Citation required The measurement they obtained enabled the astronomers to obtain a value of Template:Convert for the circumference of the Earth, (or, according to other sources, Template:Convert). The two researchers measured in Arabian Template:Transliteration, and determined the geographical latitudes of the end points they used from the star altitudes in a celestial horizontal coordinate system. As it is thought that one Arabian Template:Transliteration represented Template:Convert, they found the length of 1° of meridian to be Template:Convert, which differs from the true value by Template:Convert.Template:Citation required
Marwarrūdhī was chosen by the geometer Al-Abbās ibn Said al-Jawharī to organize a new observatory on Mount Qasioun. Despite encountering technical difficulties caused by the distortion of the astronomical instruments, in Template:Circa he spent a year obtaining of solar and lunar observations of the Sun and the Moon. He played a role in the project Template:Circa determine the length of the spring season by means of astronomical observations.Template:Sfn
Marwarrūdhī was the first of three generations of astronomers.Template:Sfn