Name

Eratosthenes

Career

Science

Occupation 1

Astronomer

Identifier

Calculated earth's circumference

Region

Africa

Era

Ancient/Medieval (to 1350)

Born

276

Died

194

Text

A North African scholar residing in Alexandria; around 210 BC. He calculated the sun's declination at different times and locations along the north/south-running Nile River. By this method he produced a relatively accurate estimate of the circumference of the earth and devised a measurement akin to latitude.

He was also a student of the Nile River and its sources.

On June 21, Eratosthenes reckoned that in Syene, which was on the Tropic of Cancer, the sun was directly overhead (90 degrees)at noontime; at Alexandria, 500 miles to the north, the noontime sun was at 82 degrees or 8 degrees on the south side from being directly overhead. He determined that 8 degrees was the equivalent of 500 miles (he used a different scale), so that 360 degrees (that in a circle as per Hipparchus) would be 360/8 x 500 = 45 x 500 = 22,500 miles, and thus the circumference of the earth.

Timeline

250 BC

Related Images

external image eratosthenes.jpg
Image Id: 1323

Related People

Hipparchus

Related Water Bodies

Nile River,

Related Source

The Story of Geographical Discovery (2004)

Related Glossary

Latitude,
Record ID:
Record ID: 16