Yeast Infection After Wax

In the third century BC lived the scientist (for me was a scientist) Greek contemporaries (envious, I suppose) nicknamed "beta" because it was the second best in everything. However, it was the first determined in a very simple and rather approximate the size of Earth.

Eratosthenes was the director of the library of Alexandria and there, referring to a scroll, read it in Siena (what is now Aswan in Egypt) on June 21 at noon did not object shadow and the light reflected directly in the bottom of the wells. Siena
was virtually the same geographical longitude Alexandria in Alexandria itself overshadowed objects, that indicated that the Earth was curved ('s well explained in the video).
Measuring the shadow, we can calculate the angle at which sunlight affect (trigonometry, which occasionally useful for something).

Earth is enough away from the sun to consider the sun's rays parallel. The angular distance between the two cities will be the same as the angle of the shadow, 7.2 °, these angles of parallel sides.

The next step was to measure the distance between the two cities, this distance is the arc corresponding to 7.2 º, simply calculate the distance that corresponds to 1 and then multiplying by 360 to calculate the length of the earth's circumference . There are different theories
on the units used by Eratosthenes to measure the distance between the two cities (as long as units, but that's for another post) the most Eratosthenes fervent supporters say they used the Egyptian stage that gave an estimate of the Earth's circumference of 39614.4 km, compared with 40,008 km currently considered, ie an error of less than 1%.

Enjoy the fantastic video of Carl Sagan (Cosmos series fragment)