【Unearth the Sphere】 How Ancients Proved Earth Was Round!

Chi-ga kun

Hakase! We know that the Earth is round, mainly from images captured by satellites.
But in the past, that wasn’t common knowledge, right? How did people in the past come to know that the Earth is round?

Hakase

In a time without satellites and the Internet, how did people come to know that the Earth is round? It’s quite a question, isn’t it?
Today, I’ll explain three pieces of evidence that prove the Earth is round!

Most people know that the Earth is spherical by looking at images captured from satellites.

However, how did people come to know that the Earth is round during a time when many believed that the Earth was flat?

Today, let’s learn together with the guinea pigs about the three main pieces of evidence that prove the Earth is round!

Evidence ①: Shadow of the Earth Seen During a Lunar Eclipse

Hakase

The first evidence that proves the Earth is round is the “shadow of the Earth seen during a lunar eclipse”.

Hakase

A lunar eclipse is a phenomenon where the sun, earth, and moon align in a straight line, and the moon becomes hidden in the shadow of the Earth.

Chi-ga kun

Ah! So, we can see the Earth’s shadow cast on the moon during this time!
Indeed, the shadow of the Earth seen during a lunar eclipse is round!

Hakase

That’s correct.
The fact that the Earth’s shadow seen during a lunar eclipse is round can be taken as evidence that the Earth is round.

Evidence ②: The Apparent Position of the North Star Based on Latitude

Hakase

The second evidence that proves the Earth is round is the “apparent position of the North Star based on latitude”.
It’s easier to understand when you compare how it would appear if the Earth was round versus if it were flat.

Hakase

The altitude of the North Star equals the latitude of the observer.
For instance, in Tokyo, which is located at latitude 36°N, the North Star appears at an altitude of 36°.

Chi-ga kun

So, if we follow the same logic, from the equator, the North Star would appear on the horizon, and from the North Pole, it would appear directly overhead!

Hakase

That’s a phenomenon that only occurs because the Earth is round.
If the Earth is flat, the altitude at which the North Star appears would remain the same, regardless of where you are.

Chi-ga kun

I see!
So, the different angles at which the North Star appears is also evidence that the Earth is round!

Evidence ③: The View of a Ship Coming into Port

Hakase

The third piece of evidence is the “view of a ship coming into port”.
Let’s assume that Chi-ga kun comes to pick me up as I board a ship entering a harbor, and let’s think about how Chi-ga kun looks at this moment.

Hakase

The earth is round, so from my eyes on the boat, I can gradually see it from Chi-ga kun’s head.

Chi-ga kun

Ah! This view wouldn’t occur if the Earth is flat.
If the Earth is flat, my entire body would appear blurred at first, and then gradually come into focus!

Hakase

That’s correct. This view from a ship entering a port can also be considered evidence that the Earth is round!

Summary

Hakase

Today we discussed three pieces of evidence that prove the Earth is round.
The three we mentioned are just a few examples; there are many more pieces of evidence that the Earth is round. Pretend you’ve gone back to a time without satellites and try to find more evidence yourself!

Chi-ga kun

The three points we learned today were methods I hadn’t even thought of before! It’s important to think beyond our current methods, such as taking pictures of the Earth from satellites.
I will try to find other evidence that the Earth is round. Thanks for today, Hakase!

Thank you for reading to the end!