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 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. 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.
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.
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.
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.
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.
He could then use simple proportions to find the Earth’s circumference — 7.2 degrees is 1/50 of 360 degrees, so 800 km 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.
Source: https://www.businessinsider.com/how-greek-eratosthenes-calculated-earth-circumference-2016-6?fbclid=IwAR2jivQpdWX3mkbtHoPeZdE3t0y-zrvG_hqMFkbZTHfGW7JdTo94JJKAhL4
ỦNG HỘ READ TO LEAD!
Chào bạn! Có thể bạn chưa biết, Read to Lead là một trang giáo dục phi lợi nhuận với mục đích góp phần phát triển cộng đồng người học tiếng Anh tại Việt Nam. Chúng tôi không yêu cầu người đọc phải trả bất kỳ chi phí nào để sử dụng các sản phẩm chất lượng của mình để mọi người đều có cơ hội học tập tốt hơn. Tuy nhiên, nếu bạn có thể, chúng tôi mong nhận được sự hỗ trợ tài chính từ bạn để duy trì hoạt động của trang và phát triển các sản phẩm mới.
Bạn có thể ủng hộ chúng tôi qua 1 trong 2 cách dưới đây.
– Cách 1: Chuyển tiền qua tài khoản Momo.
Số điện thoại 0886.630.599 (Chủ tài khoản: Nguyễn Thị Phương Thảo)
Nội dung chuyển tiền: Ủng hộ Read to Lead
hoặc
– Cách 2: Chuyển tiền qua tài khoản ngân hàng.
Ngân hàng VIB chi nhánh Hải Phòng
Số tài khoản: 012704060048394 (Chủ tài khoản: Nguyễn Tiến Trung)
Nội dung chuyển tiền: Ủng hộ Read to Lead
