Proof the Earth Is Round: Debunking Flat Earth Theory
We live in strange times. While some people launch satellites into space almost daily and create apps that let anyone identify celestial objects in real time, others still question whether our planet 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!
Contents
- Proof 1: Observe a lunar eclipse
- Proof 2: Watch a ship on the horizon
- Proof 3: Observe constellations
- Proof 4: Think about time zones
- Proof 5: Measure objects’ shadows
- Proof 6: Look at airplane routes
- Proof 7: Look at other planets
- Bonus: Look at images from space
- How to prove the Earth is round: Bottom line
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.
If the Earth were flat, its shadow would look different depending on the angle of the Sun. Instead of a perfect circle (which is only possible when the Sun is directly under the flat Earth), we might see various elliptical shapes during a lunar eclipse. However, what we observe — every single time — is a round shadow, just as you’d expect from a globe.
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, try this simple experiment: go outside, look up at the night sky, and identify a few constellations — you can do it using a stargazing app. Then ask your friend what constellations they can see. You’ll discover that certain constellations are only visible from one of the Earth’s hemispheres. For instance, the Big Dipper can’t be seen from Australia, and the Southern Cross is out of view from most of the USA.
Why is that? It’s because the curved shape of the Earth hides some constellations from our view. If the Earth were flat, everyone — no matter where they lived — would see the exact same constellations.
Want to test it out right now? Open the Sky Tonight app and try changing your location in the settings. You’ll see just how different the sky looks from another part of the globe.
Proof 4: Think about time zones
Have you ever wondered why the time in New York is 12 hours different from the time in Beijing? It’s not a political decision or some technical mistake — it’s because the Earth is a rotating sphere. As the Earth spins, different parts of it face the Sun at different times, creating day and night. Time zones exist because sunrise, noon, and sunset don’t happen simultaneously around the world.
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 in 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.
How to prove the Earth is round: Bottom line
Now you’re armed with at least seven arguments against the flat Earth theory. Observe the world around you — and do it critically! And if you want to take your curiosity even further, try using the Sky Tonight app. It lets you explore the sky from any location on Earth and see for yourself how the stars, planets, and Sun move across the celestial dome of a round, rotating planet. Also, take our quiz about Earth to test your knowledge and learn more interesting facts about our home planet.
