How to Measure the length of the circumference of Earth

How to Measure the length of the circumference of Earth

The first person to be able to estimate the length of the circumference of the earth is Eratosthenes, he was a philosof from Greek mathematician and astronomer. The method of Eratosthenes to measure the length of the circumference of the earth are as follows:

- Within one year once on a specific date when the sun is directly overhead (Summer Solstice) that is dated June 21, all the bottom of a well in Shina, now Aswan on the outskirts of the Nile (city B in the figure) exposed to sunlight, which means the sun is really straight straight.
- Elsewhere in the Alexandria (city A in the figure), on the same date exactly what he saw monuments form the image of sun
- From the incident of Eratosthenes believed that the earth is round.
- And the thought that the city of Alexandria and and Shina are on the same meridian.
- He considers that the distance between Alexandria and Shina is 5,000 stadia or approximately 800 kilo meters, because the distance is equal to 50 days of train travel with a speed of 100 stadia per day. Stadia or stage length is a measure of the sports arena that used Greek society at that time (1 stadia = approximately 185 meters).

Eratosthenes also postulate that the sunlight reaching the earth runs parallel, this is in accordance with the development of science today. Finally, on that day, according to calculations he long shadow of a pillar in Alexandria angle (angle n) is equal to the angle between the cities of Alexandria and Shina to the center of the Earth by 1 per 50 corners around the earth (approximately 7o 12 ') so that the figure around the earth: 50 x 5000 = 250,000 stadia. With mengkonfersikan finally obtained a stadia around the earth at 46,300 miles a figure that includes remarkable because only differ slightly (about 15%) than according to modern calculations, namely:
-Distance Alexandria - Shina is 729 miles instead of 800 km.
Alexandria-distance and Shina not located a meridian (diff langitude 30)
-Shina Turning Point is not located in the North but 55 km further to the north.
Angle-angular two cities instead of 7o 12 'but 7o 5'.

Method of measuring the length of the circumference of the earth that has been done by Erathostenes is a very spectacular and unusual because it occurred at 2200 years ago.