Circumfrence of your brain

Eratosthenes (276-194BC) the Greek who measured the circumfrence of the Earth within 202 miles. (He was short, and the actual distance is 24,902, so do the math.) His measurements were all accomplished using mathematics:

Eratosthenes knew that on the summer solstice at local noon in the town of Syene on the Tropic of Cancer, the sun would appear at the zenith, directly overhead. He also knew, from measurement, that in his hometown of Alexandria, the angle of elevation of the Sun would be 7.2° south of the zenith at the same time. Assuming that Alexandria was due north of Syene he concluded that the distance from Alexandria to Syene must be 7.2/360 of the total circumference of the Earth. The distance between the cities was known from caravan travellings to be about 5000 stadia: approximately 800 km. He established a final value of 700 stadia per degree, which implies a circumference of 252,000 stadia. The exact size of the stadion he used is no longer known (the common Attic stadion was about 185 m), but it is generally believed that the circumference calculated by Eratosthenes corresponds to 39,690 km [citation needed]. The estimate is over 99% of the actual distance of 40,008 km.

This same method was repeated 150 years later by Posidonius, and subsequently rejected by the Christians, who had faith that they were more intelligent and advanced than the Greeks, for about 1,400 years.

Eratosthenes was also a playwright, developed the idea of latitude, and longitude, cataloged over 650 stars, many cartographic maps, was a currator at the Library of Alexandria, and wrote a historical account back to the Trojan War. Because of all of this, he was labeled as "Beta" by his contemporaries for being second best at everything. I'm not sure if they knew they were complimenting him.

from: Wikipedia