Chalid Ben Abdulmelik al-Marwzi was a Zanji slave who was taken to Persia in the 9th century.
Together with
Ali Ben IsaAli Ibn Isa or Ali Ben Isa was an Afro-Arab astronomer, geographer and ophthalmologist in the 9th century.He wrote the landmark textbook on ophthalmology in medieval Islam, Notebook of the Oculists, for which he was known in medieval Europe as Jesu Occulist, with "Jesu" being a Latin translation...
in 827, he measured at
35 degrees northThe 35th parallel north is a circle of latitude that is 35 degrees north of the Earth's equatorial plane.In the United States, the parallel defines the southern border of Tennessee, and the border between North Carolina and Georgia....
latitudeLatitude, usually denoted by the Greek letter phi gives the location of a place on Earth north or south of the equator. Lines of Latitude are the imaginary horizontal lines shown running east-to-west on maps that run either north or south of the equator...
, in the valley of the
TigrisThe Tigris is the eastern member of the two great rivers that define Mesopotamia, along with the Euphrates. The river flows from the mountains of southeastern Turkey through Iraq.-Geography:...
, the
lengthLength is the long dimension of any object. Not to be confused with Depth which is the property of the object that appears to go away from the observer. The length of a thing is the distance between its ends, its linear extent as measured from end to end...
of a
meridianA meridian is an imaginary arc on the Earth's surface from the North Pole to the South Pole that connects all locations running along it with a given longitude. The position of a point on the meridian is given by the latitude. Each meridian is perpendicular to all circles of latitude at the...
and thus the
EarthEarth is the third planet from the Sun. It is the fifth largest of the eight planets in the solar system, and the largest of the terrestrial planets in the Solar System in terms of diameter, mass and density...
's
circumferenceThe circumference is the distance around a closed curve. Circumference is a special perimeter.-Circumference of a circle:The circumference of a circle is the length around it....
, getting a result of 40,248 km (or, according to other sources, 41,436 km). The two researchers measured in Arabian
ellAn ell , is a unit of measurement, approximating the length of a man's arm.Several national forms existed, with different lengths, including the Scottish ell , the Flemish ell and the Polish ell .In England, the ell was usually 45 inches...
, and determined the geographical latitudes of the end points they used from the
star altitudesAltitude is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object...
in a celestial
horizontal coordinate systemThe horizontal coordinate system is a celestial coordinate system that uses the observer's local horizon as the fundamental plane. This conveniently divides the sky into the upper hemisphere that you can see, and the lower hemisphere that you cannot . The pole of the upper hemisphere is called the...
.
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Chalid Ben Abdulmelik al-Marwzi was a Zanji slave who was taken to Persia in the 9th century.
Together with
Ali Ben IsaAli Ibn Isa or Ali Ben Isa was an Afro-Arab astronomer, geographer and ophthalmologist in the 9th century.He wrote the landmark textbook on ophthalmology in medieval Islam, Notebook of the Oculists, for which he was known in medieval Europe as Jesu Occulist, with "Jesu" being a Latin translation...
in 827, he measured at
35 degrees northThe 35th parallel north is a circle of latitude that is 35 degrees north of the Earth's equatorial plane.In the United States, the parallel defines the southern border of Tennessee, and the border between North Carolina and Georgia....
latitudeLatitude, usually denoted by the Greek letter phi gives the location of a place on Earth north or south of the equator. Lines of Latitude are the imaginary horizontal lines shown running east-to-west on maps that run either north or south of the equator...
, in the valley of the
TigrisThe Tigris is the eastern member of the two great rivers that define Mesopotamia, along with the Euphrates. The river flows from the mountains of southeastern Turkey through Iraq.-Geography:...
, the
lengthLength is the long dimension of any object. Not to be confused with Depth which is the property of the object that appears to go away from the observer. The length of a thing is the distance between its ends, its linear extent as measured from end to end...
of a
meridianA meridian is an imaginary arc on the Earth's surface from the North Pole to the South Pole that connects all locations running along it with a given longitude. The position of a point on the meridian is given by the latitude. Each meridian is perpendicular to all circles of latitude at the...
and thus the
EarthEarth is the third planet from the Sun. It is the fifth largest of the eight planets in the solar system, and the largest of the terrestrial planets in the Solar System in terms of diameter, mass and density...
's
circumferenceThe circumference is the distance around a closed curve. Circumference is a special perimeter.-Circumference of a circle:The circumference of a circle is the length around it....
, getting a result of 40,248 km (or, according to other sources, 41,436 km). The two researchers measured in Arabian
ellAn ell , is a unit of measurement, approximating the length of a man's arm.Several national forms existed, with different lengths, including the Scottish ell , the Flemish ell and the Polish ell .In England, the ell was usually 45 inches...
, and determined the geographical latitudes of the end points they used from the
star altitudesAltitude is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object...
in a celestial
horizontal coordinate systemThe horizontal coordinate system is a celestial coordinate system that uses the observer's local horizon as the fundamental plane. This conveniently divides the sky into the upper hemisphere that you can see, and the lower hemisphere that you cannot . The pole of the upper hemisphere is called the...
. 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 850 metres.