2000多年前古希臘人就已經知道地球周長英語美文

In the mid-20th century, we began launching satellites into space that would help us determine the exact circumference of the Earth: 40,030 km. But over 2000 years earlier, a man in Ancient Greece came up with nearly the exact same figure using just a stick and his brain. Following is a transcript of the video.

20世紀中期，我們開始向太空發射衞星，從而幫助我們確定了地球的精確周長為40,030公里。然而，早在2000年前，古希臘的一個人僅用一根棍子和他的大腦，得到了一個幾乎完全相同的數字。以下是該視頻的文字記錄。

How an ancient Greek mathematician calculated the Earth’s circumference. In the mid-20th century, we began launching satellites into space that would help us determine the exact circumference of the Earth, 40,030 km.

一名古希臘人是如何計算出地球的周長的?20世紀中期我們才開始往太空發射衞星，幫助我們確定了地球的真實周長為40,030公里。

But over 2,000 years earlier in ancient Greece, a man arrived at nearly that exact same figure by putting a stick in the ground. That man was Eratosthenes. A Greek mathematician and the head of the library at Alexandria.

但是在兩千多年前的古希臘已經有一個人僅用一根棍子和他的大腦，得到了一個幾乎完全相同的數字。這個人就是埃拉托色尼，古希臘的.一位數學家、亞歷山大里亞圖書館的館長。

Eratosthenes had heard that in Syene, a city south of Alexandria, no vertical shadows were cast at noon on the summer solstice. The sun was directly overhead. He wondered if this were also true in Alexandria.

埃拉托色尼曾聽説，在亞歷山大港南部的賽尼城，夏至那天正午時垂直的物體沒有出現影子，太陽直射在頭頂上。他思考着在亞歷山大港是否也是如此。

So, on June 21 he planted a stick directly in the ground and waited to see if a shadow would be cast at noon. It turns out there was one. And it measured about 7 degrees.

因此，在6月21日夏至那天，他把一根棍子垂直插在地上，等着看在正午時會不會出現影子。結果發現有影子，測量發現太陽光線與地面的角度為7度。

Now, if the sun’s rays are coming in at the same angle at the same time of day, and a stick in Alexandria is casting a shadow while a stick in Syene is not, it must mean that the Earth’s surface is curved. And Eratosthenes probably already knew that.

那麼，如果太陽光線在一天的同一時間以同樣的角度照射進來，亞歷山大港的一根棍子在地上投射出了影子，賽尼城的卻沒有影子，那麼它一定意味着地球的表面是彎曲的。因此，埃拉托色尼很可能已經知道地球是圓球體。

The idea of a spherical Earth was floated around by Pythagoras around 500 BC and validated by Aristotle a couple centuries later. If the Earth really was a sphere, Eratosthenes could use his observations to estimate the circumference of the entire planet.

畢達哥拉斯在約公元前500年就提出了一個球形地球的概念，並被幾個世紀後的亞里士多德證實。如果地球真的是一個球體，埃拉托色尼可以用他的觀測來估計整個地球的周長。

Since the difference in shadow length is 7 degrees in Alexandria and Syene, that means the two cities are 7 degrees apart on Earth’s 360-degrees surface. Eratosthenes hired a man to pace the distance between the two cities and learned they were 5,000 stadia apart, which is about 800 kilometers.

由於亞歷山大港和賽尼城的陰影長度的差異是7度，這意味着這兩個城市在地球360度的表面上相距7度。於是埃拉托色尼僱了一個人來測量這兩個城市之間的距離，得知兩者相距約5000視距尺，大約是800公里。

He could then use simple proportions to find the Earth’s circumference — 7.2 degrees is 1/50 of 360 degrees, so 800 times 50 equals 40,000 kilometers. And just like that, a man 2200 years ago found the circumference of our entire planet with just a stick and his brain.

然後，他使用簡單的比例公式計算出了地球的周長——7.2度是360度的50分之1，因此，800乘以50就午到了40000公里。就是這樣，2200年前的這個人僅用一根棍子和他的大腦，就知道了地球的周長。

This video was produced by Alex Kuzoian.

該視頻由亞歷克斯製作。