Earth's circumference

thumb|Measured around the equator, it is 40,075.017 km (24,901.461 mi) Earth's circumference is the distance around Earth. Quotes In making his own calculation, however, Christopher Columbus preferred the values given by the medieval Persian geographer, Alfraganus: one degree (at the equator) is equal to 56.67 miles. That was Columbus’s first error, which he compounded with a second: he assumed that the Persian was using the 4 856-foot Roman mile; in fact, Alfraganus meant the 7 091-foot Arabic mile.Taken together, the two miscalculations effectively reduced the planetary waistline to 16,305 nautical miles, down from the actual 21,600 or so, an error of 25 percent. Columbus’s Geographical Miscalculations, IEEE Spectrum (08 Oct 2012) You climb a mountain situated close to the sea or a level plain, and then observe the setting of the sun and find out the dip of the horizon... [Then] find the value of the perpendicular of the mountain. You multiply this height into the sine of the complementary angle of the dip, and divide the total by the versed sine of this dip itself. Then multiply (twice) the quotient into 22 and divide the result by 7. You will get the... earth's circumference (in the same units) in which the height of the mountain has been found. Al Birüni in his Kitàb al Tahdid. quoted in C. K. Raju, Cultural Foundations of Mathematics, Vol. 10, Pt. 4: The Nature of Mathematical Proof and the Transmission of the Calculus from India to Europe (India: Pearson Longman, 2007) External links Category:Astronomy Category:Earth