Debunking Flat Earth Theory: How to Prove Earth Is Round

We live in strange times. While some people are getting ready to send astronauts to Mars in just a few years, other people, apparently, still don’t believe the Earth is round. Although the very existence of the “flat-Earth theory” is quite discouraging, we’d like to use it in a positive way – as an exercise in critical thinking. Can you tell for yourself that the Earth is not flat? Yes, you can, and we’ll tell you how!


Proof 1: Observe a lunar eclipse

A lunar eclipse occurs when the Earth comes between the Sun and the Moon, casting a shadow over our natural satellite. If you look at the Earth’s shadow during a lunar eclipse, you’ll notice that it is curved – like a part of a circle. Moreover, the Earth’s shadow on the Moon is ALWAYS circular at every lunar eclipse and doesn’t change with the Earth’s rotation. The only shape that makes a perfectly circular shadow every single time, no matter the object’s orientation, is a sphere.

Someone might argue that a flat disk can also produce a round shadow. Yes, it can, but only at a certain illumination angle – when it’s perpendicular to the Sun’s rays. But in this case the Sun would have to be positioned beneath the flat disk, and flat-Earthers claim that the Sun always hovers above it, shining like a spotlight.

To better understand the mechanics of lunar eclipses, watch our video.

Proof 2: Watch a ship on the horizon

Grab a pair of binoculars, go to the seashore, and watch a ship sail away. If the Earth were flat, the entire ship would always stay in view, it would only get smaller and smaller. In reality, though, ships on the horizon disappear hull-first, and the last thing that sinks below the horizon is the top of the ship’s mast. This happens because of the Earth’s curvature.

Proof 3: Observe constellations

If you have a friend who lives in another hemisphere, do the following. Look up at the sky, find some constellations, and then ask your friend what constellations they can see. You’ll learn that certain constellations are visible only from one of the Earth’s hemispheres. For example, the Big Dipper asterism is not visible from Australia, and the Southern Cross cannot be seen from most of the USA.

This happens because the Earth’s curvature hides some of the constellations from our view. If the Earth were a flat disk, everyone would see the same set of constellations.

Proof 4: Think about time zones

Why is the time in New York 12 hours different from the time in Beijing? The thing is, when New York is illuminated by the Sun, the other side of the planet – where Beijing is located – is completely dark. This happens because the Earth is a sphere rotating around its axis.

Flat-Earthers argue that time zones are also possible with their model because the Sun shines more like a spotlight, emitting light only on a specific location. However, in this case, we should be able to see the Sun in the sky all the time, even if its light doesn’t fall directly on us. In reality, we don’t see the Sun at night, so this model is obviously incorrect.

Proof 5: Measure objects’ shadows

For this experiment, you’ll need a friend who lives at least a few kilometers from you. On a sunny day, both of you should take identical sticks, place them in the ground at the right angle and at the same instant of time, and measure the length of the shadow. You’ll find out that the shadows have different lengths!

The reason for this is, again, the Earth’s curvature. As the sticks are far enough apart, the sunlight hits them at different angles. Flat-Earthers’ “spotlight Sun” concept could also have explained this phenomenon, but we’ve already told you why this concept is not valid.

Proof 6: Look at airplane routes

As an example, let’s take a flight from Santiago, Chile, to Sydney, Australia. On a flat Earth, the shortest route would look like this: a plane would have to fly across all of South America, all of North America, and only then over the ocean to Sydney. Which way do real planes travel between these two cities? Just google it, and you’ll find out that commercial airplanes only need to cross the Pacific Ocean to fly from Santiago to Sydney. If you don’t trust Google, take such a flight yourself, look out the airplane window, and try to spot North America beneath you while you fly.

Proof 7: Look at other planets

Here’s a fact: there are no flat planets in the Solar System. You can take a telescope and observe Venus, Mars, Jupiter, or Saturn. These planets differ a lot by their physical properties, but all of them are spherical. Why would the Earth be THAT physically different from all other planets in the Solar System? This argument might not convince a devout flat-Earther, but it’s worth thinking about anyway.

Bonus: Look at images from space

Since the launch of Sputnik 1 in 1957, scientists have sent countless probes and satellites into space – including the International Space Station, where astronauts constantly work. As a result, we received tons of amazing high-quality pictures of our planet. In these pictures, you can clearly see that the Earth is a sphere.

Now you’re armed with at least 7 arguments against a flat-Earther. If you liked this article, please share it with your friends on social media. Observe the world around you and do it critically!