Earth's circumference | Wikipedia audio article
Channel: wikipedia tts
Date: 2019-05-15

This is an audio version of the Wikipedia Article:
https://en.wikipedia.org/wiki/Earth%27s_circumference


00:02:29 1 History of calculation
00:09:24 2 Historical use in the definition of units of measurement
00:13:41 3 Bibliography
00:15:29 4 See also



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SUMMARY
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Earth's circumference is the distance around the Earth, either around the equator (40,075.017 km [ 24,901.461 mi ]) or around the poles (40,007.86 km [ 24,859.73 mi ]).
Measurement of Earth's circumference has been important to navigation since ancient times. It was first calculated by Eratosthenes, which he did by comparing altitudes of the mid-day sun at two places a known north–south distance apart. In the Middle Ages, Al Biruni calculated a more accurate version, becoming the first person to perform the calculation based on data from a single location.
In modern times, Earth's circumference has been used to define fundamental units of measurement of length: the nautical mile in the seventeenth century and the metre in the eighteenth. Earth's polar circumference is very near to 21,600 nautical miles because the nautical mile was intended to express 1/60TH of a degree of latitude (i.e. 60 × 360), which is 21,600 partitions of the polar circumference. The polar circumference is even closer to 40,000 kilometres because the metre was originally defined to be one 10-millionth the distance from pole to equator. The physical length of each unit of measure has remained close to what it was determined to be at the time, but the precision of measuring the circumference has improved since then.
Treated as a sphere, determining Earth's circumference would be its single most important measurement (Earth actually deviates from a sphere by about 0.3% as characterized by flattening).