We all know the Earth is round. Not perfectly so but close enough. We live on an oblate spheroid, a slightly squashed sphere that's wider at the equator than around the poles. The difference between the planet's polar and equatorial diameter isn't much — just 27 miles (43 km) and not apparent to the eye.

Earth's a little wider around the middle because rock and water are stretchy or plastic. As the planet spins it bulges out at the equator. Jupiter's outer layers are composed of gas and clouds, and it spins rapidly, completing a rotation in just under 10 hours. Because vapory material is much more pliant than hard rock Jupiter has a much bigger equatorial bulge. Seen though the telescope it's immediately apparent that its shape resembles a fully loaded hamburger.

Two views of the Flat Earth model from the Flat Earth Society. In both views we are looking down at the flat Earth. The diagram on the shows the sun and moon which are assumed to be quite nearby and illuminate only parts of the planet like spotlights. Flat Earth Society / CC BY-SA 4.0
Two views of the Flat Earth model from the Flat Earth Society. In both views we are looking down at the flat Earth. The diagram on the shows the sun and moon which are assumed to be quite nearby and illuminate only parts of the planet like spotlights. Flat Earth Society / CC BY-SA 4.0

We've known we live on a globe for a long time, so you might be surprised that a YouGov poll of 8,215 U.S. adults in February 2018 found that 2% of Americans firmly believe the Earth is flat. Young adults, ages 18 to 24, are likelier than any other age group to say they believe the Earth is flat (4%).

In recent years the flat Earth idea has seen a resurgence for several reasons including misinformation, lack of trust in institutions and the desire to create a non-fact-based reality to justify a point of view. While I find the Flat Earth concept dispiriting, the upside is that it makes us stop and wonder how we know what we know.

WDAY logo
listen live
watch live
Newsletter signup for email alerts

You and I have no problem with a spherical Earth. If nothing else, the thousands of images and videos taken by satellites, space probes and astronauts on board the space station have proven beyond a shadow that we live on a globe. But wouldn't it be nice if you could prove it in the flesh, too? Well, you can!

In honor of Nov. 10 as World Science Day of Peace and Development — a celebration highlighting the importance of science in society — here are seven ways you can show your doubting friends (and convince yourself) we live on a big ball and not a cheese pizza.

#1 Observe a lunar eclipse

The shadow cast by a spherical body like the Earth is circular as seen in this lunar eclipse sequence from Dec. 21, 2010. (Tuanna 2010 / CC BY-SA 3.0)
The shadow cast by a spherical body like the Earth is circular as seen in this lunar eclipse sequence from Dec. 21, 2010. (Tuanna 2010 / CC BY-SA 3.0)

Thousands of years ago the ancient Greeks concluded the Earth must be spherical because it cast a curved shadow on the moon at every lunar eclipse. Imagine spinning a volleyball or soccer ball on your fingertip on a sunny afternoon. No matter what side of the ball faces the sun it casts a round shadow.

A spherical body like the Earth, sun, moon and planets casts a circular shadow. (Bob King)
A spherical body like the Earth, sun, moon and planets casts a circular shadow. (Bob King)

Some might argue that a flat disk also casts a circular shadow. But keep in mind that the Earth rotates. If the planet were a spinning disk its shadow would vary at every lunar eclipse. If one side of the disk were face-on to the sun at the time of total eclipse it would cast a circular shadow on the moon just like normal. But if disk were edge-on to the sun at the time, its shadow would be a fuzzy, gray stripe across the moon's face.

If the Earth were a flat disk instead of a sphere its shadow during lunar eclipses would vary from a circle to a strip. (Bob King)
If the Earth were a flat disk instead of a sphere its shadow during lunar eclipses would vary from a circle to a strip. (Bob King)

Of course, that's not what we see. Earth's shadow appears identical at each and every eclipse, proving beyond a doubt that we live on a sphere. Remember the volleyball? Its shape is symmetrical with no preferred orientation, just like the Earth. You'll get your chance to see this for yourself twice in 2021 during lunar eclipses on May 26 and Nov. 19, both of which will be visible across the Americas.

#2 Climb a hill

On a curved surface the higher up you are the farther you can see. If you're on a mountaintop the vista is immense compared to a similar view at sea level. An airplane's even better. Every climb in elevation lets you see a little further beyond the horizon. On a flat surface you would see everything all at once both close and far. Objects in the distance would appear smaller for sure, but with powerful enough telescope you could presumably see to the ends of the Earth.

If you're quick it's possible to see the sun rise or set twice in a day, but it's easier to perform the sunrise-sunset experiment with the help of friend. (Bob King)
If you're quick it's possible to see the sun rise or set twice in a day, but it's easier to perform the sunrise-sunset experiment with the help of friend. (Bob King)

But that's not what we observe. A sphere's curvature hides distant objects. To see them you have to climb up a hill or fly higher. One of the best ways to experience this is to invite a friend for a (very) socially distant sunrise. You'll need a lake or a big field with a good view down to the horizon and a nearby hilltop with the same. One of you watches from the lake shore, the other from the hill. Being higher up, the hilltop observer will see the sun rise earlier.

If the lake stands at 600 feet elevation and the hill at 1,500 feet, your lucky hilltop friend will see the first peep of sun more than 2 minutes before you. As well, he'll see sunset extended by the same amount of time. You can try this experiment alone to see the sun set twice by quickly climbing a tree, a tall ladder or jetting to the top of a building in a fast elevator. Be careful!

Steven Wooding, a physicist from Southampton, UK, created a wonderful sunset calculator that will help you to find out how many extra seconds of sunset you'll get depending on how high you climb. Brilliant! I used it in the example above.

#3 Watch a ship come in

This photo of Thorntonbank Wind Farm (near the Belgian coast) clearly demonstrates how the curvature of the Earth blocks parts of the distant wind turbines. The greater the distance the more the towers become increasingly hidden by the horizon. On a flat planet we would see the towers from top to bottom. (Lieven / CC BY-SA 4.0)
This photo of Thorntonbank Wind Farm (near the Belgian coast) clearly demonstrates how the curvature of the Earth blocks parts of the distant wind turbines. The greater the distance the more the towers become increasingly hidden by the horizon. On a flat planet we would see the towers from top to bottom. (Lieven / CC BY-SA 4.0)

This is a variation on the previous exercise demonstrating how the curvature of the Earth hides objects in the distance. Once again we head down to the lake or sea shore. On a flat Earth, a distant ship would appear tiny but complete and then grow larger as it moved closer.

This illustration demonstrate how the curvature of the Earth "gets in the way" or hides parts of distant objects like a boat or lighthouse.  The observer here sees only the top of the mast and the lighthouse light. (Efa with additions by the author / CC BY-SA 3.0)
This illustration demonstrate how the curvature of the Earth "gets in the way" or hides parts of distant objects like a boat or lighthouse. The observer here sees only the top of the mast and the lighthouse light. (Efa with additions by the author / CC BY-SA 3.0)

On a spherical Earth a ship slowly "grows" from the horizon. First we see the mast, then the sail and deck and finally the hull — clear proof that the Earth's spherical bulk gets in the way until the boat is close enough for the curvature to be so miniscule it becomes irrelevant.

Over short distances the Earth does look flat, an obvious source of confusion for some Flat-earthers. But over long distances the curvature becomes very obvious.

#4 Go for a plane ride

Gosh, we all need a vacation about now. The next time you're on a plane consider that if you kept flying you'd make a complete circle around the globe and return back to exactly where you started. There are no edges and no drop-offs. On a flat Earth you would fly to the edge and then meet ... a void. To return home the pilot would have to turn the plane around and backtrack. On a sphere you can go home without turning around.

#5 Constellations change with latitude

There's a reason Chicagoans can't see the Southern Cross, and the Big Dipper is invisible from Australia. For each, those stars are hidden by the curvature of the globe, the same reason I can't use a telescope to see Paris from my house. Paris is below my horizon. So is the Southern Cross and lots of other southern sky sights. To see them I have to fly or drive hundreds of miles south over the curved Earth to the tip of Florida where these stars are in full view.

The horizon cuts off the Southern Cross from Chicago, but if you travel around the curve of the Earth to Key West it will come into view. (Stellarium)
The horizon cuts off the Southern Cross from Chicago, but if you travel around the curve of the Earth to Key West it will come into view. (Stellarium)

On a flat Earth everyone would see the same set of constellations no matter where they stood on the pizza. And because the Earth doesn't rotate in the Flat Earth model the stars merely circle above, never rising or setting. Yet another contradiction of reality.

#6 Sun here, darkness there

When the sun is shining on one the side of the Earth the opposite side is dark. Because the planet rotates, the dark side will eventually turn back into the sun just as the sunlit half turns to greet the night. To keep track of what time it is where, in 1883 Canada's Sir Sandford Fleming proposed dividing the globe into 24 time zones. If it's 3 p.m. in Des Moines it's 6 p.m. in Buenos Aires and 8 a.m. the next morning in Ulaanbaatar, Mongolia.

On a flat Earth the sun would be visible simultaneously from everywhere, and due to its great distance from us, would appear at nearly the same altitude no matter if you stood at the center or along the edge of the disk. Flat Earthers argue that the sun is close and more like a spotlight, but for the sun to appear at different elevations in the sky it would have be much closer than the moon, in which case the planet would be toast.

#7 Look at the moon and other planets

The moon and every one of the planets looks round through a telescope. They also all rotate including the moon, but its rotation is synchronized with its revolution around the Earth, so we only see one face. Trust me, it spins — every 27.3 days.

All the other planets are spherical. Why not Earth? (Lsmpascal / CC BY-SA 3.0)
All the other planets are spherical. Why not Earth? (Lsmpascal / CC BY-SA 3.0)

If the planets were pizzas like the flat Earth then we would see their shapes change as they spun on their axes. Let's take Mars for example, currently high and bright in the evening sky. One moment it would appear circular or normal, but as it rotated the circle would narrow to an oval. And that oval would narrow further until Mars turned edge-on to us and looked like a toothpick! Then it would gradually open up and fill out into a circle again. Of course, that's not what we see.

If the planets are spheres, and Earth is a planet, then you would expect it to be spherical, too, Photos of Earth from space show exactly that.

Just like that airplane ride, we've come full circle. Anyone in the mood to play ball?



"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.