# The Earth is Round: Here’s a Cool Experiment to Prove It

There are rumors that the Earth might be flat. You would think that whether the Earth was shaped like a ball or a plate would have been settled a long time ago. In fact, it was—2,500 years ago. Even the ancient Greeks knew the Earth was round. But that doesn’t stop some people today from believing otherwise or keep them from trying to convince others of a flat Earth as well.

People lucky enough to travel high above the ground in spaceships are able to see the curve of the Earth for themselves. But unless you’re an astronaut, that isn’t easy to do. However, you don’t need to be an astronaut to prove that the Earth is round for yourself. You can do it the same way that the Greeks did so long ago. All it will take is a protractor, string, a weight, and a road trip.

If you were at the North Pole standing on the porch of Santa’s workshop, you would see Polaris, the “North Star,” directly over your head. It would be at a 90-degree angle above the horizon.

This angle between Polaris and your horizon is equal to your latitude on the Earth. Measuring it has been the standard practice of sailors, explorers, and cartographers for centuries.

As you walked away from the North Pole and back to warmer climates, you would find that Polaris was no longer directly overhead. Instead, Polaris would start to move down toward the Northern horizon. The farther away you got from the North Pole, the lower Polaris would appear in the sky

If the Earth were completely flat, you should be able to see Polaris from anywhere on the planet—from the North Pole to Australia and beyond. On a round Earth, however, Polaris cannot be seen once you cross the equator.

## Try this at-home experiment

You can test this theory for yourself at home. You can measure your latitude on the Earth by using a protractor and a plumb bob (a weight attached to the end of a string).

## Directions

1. First, locate Polaris in the night sky. You can find Polaris by looking for the Big Dipper. Once you find the Big Dipper, the two outermost stars in its bowl will point to Polaris.

2. Attach the plumb bob to the center of the protractor. When the string is free, the weight will pull it directly downward (as long as gravity is working, of course). When the protractor is level, the string will line up with the 90-degree mark on the protractor

3. Next, sight along the edge of the protractor and raise your head until you are looking along the protractor’s edge at Polaris. The string will now be at a different angle. (I don’t recommend doing this if you are sailing on a boat in rough seas. There is a reason that pirates wear eye patches.)

4. Once you make the sighting of Polaris, hold the string in place while you look where it lays on the side of the protractor. The difference between 90 degrees and the angle that you measure is exactly the same as the angle from the horizon to Polaris — your latitude.

It turns out that each degree of latitude corresponds to about 70 miles due south.  If you travel about 250 miles from your home either to the north or the south, you should be able to see the difference in your latitude using the same device.

With 70 miles per degree of latitude, it takes just over 6,000 miles from the North Pole until your latitude is zero (90 times 70). Another look at the map will show that 6,000 miles from the North Pole puts you right on the equator, where Polaris will dip below the northern horizon. Polaris won’t be visible if you travel any farther south.

So armed with these facts — that Polaris is not visible from the southern hemisphere and the ability to confirm changes in latitude with your own measurements — you can contradict the prediction of a flat Earth.

## Glossary

Protractor: an instrument for measuring angles, typically in the form of a flat semicircle marked with degrees along the curved edge

Polaris: Commonly known as the North Star or Pole Star, is the brightest star in the constellation of Ursa Minor.

Latitude: Latitude is an angle which ranges from 0° at the Equator to 90° at the poles.

Cartographer: a person who draws or produces maps.

Equator: an imaginary line drawn around the earth equally distant from both poles, dividing the earth into northern and southern hemispheres and constituting the parallel of latitude 0°

Jason Steffen is an assistant professor of physics and astronomy at the University of Nevada, Las Vegas. Steffen works in the field of exoplanets (planets that orbit distant stars) and has a history in experimental studies of dark matter, dark energy, and gravity. For more than 10 years, Steffen was also a member of the science team for NASA’s Kepler mission. Discoveries from that mission revolutionized our understanding of planets and planetary systems.

## Contributors

• : Author
Jason Steffen is an assistant professor of physics and astronomy at the University of Nevada, Las Vegas. Steffen works in the field of exoplanets (planets that orbit distant stars) and has a history in experimental studies of dark matter, dark energy, and gravity. For more than 10 years, Steffen was also a member of the science team for NASA’s Kepler mission. Discoveries from that mission revolutionized our understanding of planets and planetary systems.

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