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。

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。

Eratosthenes was intrigued by this story.

埃拉托色尼对这个故事很感兴趣。

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。

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。

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。

Aristotle also thought that the earth was smaller than the other planets; a claim that was challenged by Eratosthenes, who used the shadows of sundials in Alexandria and Syene to calculate the circumference of the earth.

亚里士多德还认为地球比其他行星小；埃拉托色尼对这一说法提出了质疑，他使用亚历山大和赛伊尼的日冕阴影来计算地球的周长。