About a matter of two hundred decades ago, Greek astronomers valued the erudition that the shape of the Earth is correspondingly a sphere. And as the moon passes through the shadow of the earth, or that which is called a lunar eclipse, the Greeks have observed the circular shadow casted by the Earth. Since that time, it was already an established intellect that only spherical objects cast a circular shadow, thus, the conclusion that the Earth is likewise spherical in shape.
The mere conclusion of the Earth’s shape, nevertheless, did not achieve contentment to the Greeks.
A Greek astronomer by the name Eratoshenes discovered a possible way in measuring the Earth’s circumference. It started when he had heard some reports from one of Egypt’s city, Syene, which was located on the equator of the earth. The reports have informed Eratosthenes that the sun shows vertical wells down on Syene during the first day of summer. However, the astronomer did not observe any similar phenomenon anywhere by his home; therefore he arrived at the supposition that in his home, Alexandria, which lies 7 degrees north of the city of Syene, the sun never does reach zenith.
Eratoshenes further presupposed that the sun is in line with the potential measurement of about 7 degrees south of his residency’s zenith during summer solstice or the first day of summer. Provided such conclusion, the distance from Alexandria and Syene was believed to be 7/360 or 1/150 that of the circumference of the Earth ( a complete circle has a 360 degree measure).
Additionally, way back Eratoshenes’ time, “stade” was the known standard unit of measurement, which then is equal to 1/6 of a kilometer.
Consequently, there are 5,000 stades from Syene to Alexandria and from such logic, the Earth’s circumference was calculated to be: 50 x 25,000 stades = 42,000 kilometers. Accordingly, the accepted modern value of the Earth’s circumference is 40,000 km, hence Eratosthenes was correct.
References
“The Earth and Moon, Size of the Earth cont. ” Publication retrieved on 10 Sept 2007 from http://inkido. indiana. edu/a100/earthmoon7. html
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