Show Summary Details

Page of

PRINTED FROM OXFORD REFERENCE (www.oxfordreference.com). (c) Copyright Oxford University Press, 2023. All Rights Reserved. Under the terms of the licence agreement, an individual user may print out a PDF of a single entry from a reference work in OR for personal use (for details see Privacy Policy and Legal Notice).

date: 14 June 2024

Eratosthenes (c.276–c.194 bc) Greek writer 

A Dictionary of Astronomy

Ian Ridpath

on many subjects, born in modern Libya. He made the first known calculation of the Earth's circumference that was based on a scientifically sound method. According to tradition, he did this by measuring the Sun's altitude as seen from Alexandria at the summer solstice, when he knew the Sun to be overhead at Syene, some 1000 km to the south. However, it is possible that he may actually have used a simpler method, which is to measure the amount by which the angle from the zenith to the horizon exceeded 90° as seen from a high point, such as a lighthouse. The effect of atmospheric refraction would give a result about 15% in excess of the true value, which is what he obtained. Eratosthenes also measured the ... ...

Access to the complete content on Oxford Reference requires a subscription or purchase. Public users are able to search the site and view the abstracts and keywords for each book and chapter without a subscription.

Please subscribe or login to access full text content.

If you have purchased a print title that contains an access token, please see the token for information about how to register your code.

For questions on access or troubleshooting, please check our FAQs, and if you can''t find the answer there, please contact us.