毎日英語学習

毎日英語学習のアウトプットに作りました。

これが少しでも誰かに為になればと思います。

今回のテーマは天文学者の

エラトステネスです。

Eratosthenes

Many scientists in Ancient Greece believed  the world was round.

But none of theme knew how big it was until the third century BC when Eratosthenes (c.276-194 BC), chief librarian of Alexandria, devised an ingenious way to measure the earth’s size.

Eratosthenes knew of a special well near Syene, Egypt.

At noon on June 21, the longest day of the years, the sun’s rays penetrated all the way to the bottom of the well.

This  meant that the sun was directly overhead.

Eratosthenes realized that if the sun was directly overhead in Senen, then its rays must be hitting at angle in Alexandria, which was due north.

If he could measure the angle by which the sun was off center, then he would have the clue he needed to extrapolate the size of the earth.

So, at noon on June 21 in Alexandria, he took a measuring stick and captured the angle cast by its shadow.

Eratosthenes knew that the angle of the shadow was equivalent to the angle formed by the two cities and the center of the earth.

So, he divided the size of that angle by 360, the number of degrees in a circle, to determine the fraction of  the earth that separated the two cities.

The answer was one-fiftieth.

In other  words, if you walked the equivalent of the earth’s circumference.

All that remained was to measure the precise distance between the two cities.

Eratosthenes hired a pacer, a professional walker trained in taking perfectly equal steps.

From the measurements of the pacer, Eratosthenes estimated the circumstance of earth to be 24,700 miles.

Today, using the same principles developed by Eratosthenes 2,000 years ago, modern instruments estimate the distance around the equator to be 24,902 miles.

In Eratosthenes’s time, the know world extended from Spain to India. 

He believed that a vast ocean covered the rest of the world.

If it weren’t for the enormity of the ocean, Eratosthenes thought it would be possible to sail from Spain to India by heading west.

It was this idea that inspired Christopher Columbus to undertake his famous voyage in 1492.