Introduction to Earth Sciences I

1.1 The Earth's Size and Shape

Centuries ago people had very little idea about the total size of the Earth and hardly any notion of its shape. Few people traveled very far because transportation was difficult. So the total size of the Earth became an early object of inquiry.

One of the earliest attempts to estimate the Earth's size was done by Erastosthenes about 200 B.C. His deduction was based on a curious observation (his data) that intrigued him. He lived in Alexandria but had heard that in Syene, on the longest day of the year, the sun at midday shone directly down a well without making a shadow - meaning that it was absolutely overhead at that time. He also knew that this was not true on the same day in his hometown of Alexandria, and this puzzled him a lot. His deduction allowed the size of the Earth to be estimated.

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