There was a really brilliant Greek scientist called Eratosthenes.

那时有个非常聪明的希腊科学家，名叫艾尔托斯蒂尼。

Over 2000 years ago, the Greek philosopher Eratosthenes figured it out.

2000多年前，希腊哲学家埃拉托色尼(Eratosthenes)找到了答案。

In the 3rd century BCE, Eratosthenes estimated the circumference of the planet.

公元前3世纪，埃拉托色尼估计了地球的周长。

Eratosthenes was intrigued by this story.

埃拉托色尼对这个故事很感兴趣。

Like one summer day, Eratosthenes observed shadows in different Egyptian cities so that he could calculate the size of the earth.

例如在一个夏日，埃拉托色尼观察了埃及不同城市的阴影，这样他就可以计算出地球的大小。

On the day of the solstice, Eratosthenes stuck a stick in the ground in Alexandria and measured the angle of its shadow.

夏至那天，埃拉托色尼将一根棍子插在亚历山大的地上，测量了它的影子的角度。

But there's also a remarkably quick and elegant solution inspired by an idea that's thousands of years old: the sieve of Eratosthenes.

但也有一个非常快速和优雅的解决方案，其灵感来自一个具有数千年历史的想法：Eratosthenes 的筛子。

Eratosthenes of Cyrene was a 3rd century BCE mathematician from ancient Greece interested in prime numbers, that is numbers only divisible by 1 and themselves.

Cyrene 的埃拉托色尼 (Eratosthenes of Cyrene) 是公元前 3 世纪来自古希腊的数学家，他对素数很感兴趣，素数只能被 1 和它们本身整除。

1,600 years before Columbus set sail, Eratosthenes not only realized the earth was round, but calculated its circumference and diameter within a few miles of their actual size.

在哥伦布出海航行的 1600 年前，埃拉托斯特尼不仅发现地球是圆的，还算出了地球的周长和直径，计算结果与实际仅差几英里。

And Eratosthenes noticed that there was a town called Syene, and on a certain date the sun would actually shine straight down to the bottom of a well.

艾尔托斯蒂尼注意到，在一个叫作塞尼的小镇，太阳光会在特定的日期直射到井的底部。