Curvature of the Earth

Earth’s Curvature: How High Must You Be to See It?

At what altitude can you start seeing the curvature of the Earth? Is it visible from the top of a skyscraper, a mountain peak, or a passenger plane? Can a high-altitude balloon provide a clear view, or is it something you can only witness from space?

Most people don’t realize how large the Earth is compared to the height of a mountain or the altitude of a passenger aircraft. It’s easy to think we’re really high up when standing on a mountain peak or flying in a passenger plane. However, even at these heights, we’re just skimming the surface of our planet. For perspective, commercial aircraft typically fly between 31,000 and 38,000 feet (about 5.9 to 7.2 miles) high, which is higher than even Mount Everest, the tallest mountain on Earth.

So, how high do you have to be to see the curvature of the Earth?

Key Takeaways:

  • The curvature of the Earth (actually the curvature of the Earth’s horizon) becomes visually discernible from an altitude of around 35,000 feet (10,600 meters), assuming clear conditions and a wide field of view.
  • Ancient civilizations inferred Earth’s curvature through observations like disappearing ships on the horizon.
  • You can’t see the curvature of the Earth from a homemade rocket. The Earth’s massive size makes its curvature difficult to observe at lower altitudes.

What Do You Mean by the “Curvature of the Earth”?

You can observe the curvature of the Earth even at sea level. The ancient Greeks knew the Earth was round: a ship moving toward the viewer on the horizon will gradually appear with the masts first, followed by the superstructure, and finally the hull.

From just 3 meters (10 feet) above the surface, you can see the horizon 6.2 km (3.85 miles) away. If you’re 30 meters (100 feet) high, you’ll be able to see up to 20 km (12.5 miles) away. This is one of the reasons ancient civilizations understood that the Earth was curved, not flat, as early as the sixth century BC.

The top of the Boston skyline is just barely visible from Cape Cod, because of the curvature of the Earth
The top of the Boston skyline is just barely visible from Cape Cod, because of Earth’s curvature
Curvature of Earth: wind turbines
This image of Thorntonbank Wind Farm (near the Belgian coast) with the lower parts of the more distant towers increasingly hidden by the horizon, demonstrates the curvature of the Earth. Photo by the Wikipedia user Lieven – Own work, CC BY-SA 4.0, Link

So, the real question here is: “At what altitude can you start seeing the curvature of your horizon?”

Spoiler: you have to be a lot higher than that flat-earther ‘Mad’ Mike Hughes who died while trying to reach an altitude of 5,000 feet (1,525 meters) while riding his steam-powered rocket to “prove” the Earth is flat. He could climb a mountain to reach a higher altitude than launching himself onboard his homemade stupid “rocket”. He still wouldn’t see the curvature of Earth (actually the curvature of the horizon), though, but that would prove nothing. Earth is big.

Curvature of the Earth - Earth and moon from the ISS (Photo: Nick Hague)
NASA astronaut Nick Hague took an amazing photo of the Earth and moon from the International Space Station (ISS) and published it on his Twitter account, saying “Good night from space station”. Even though orbiting Earth at a distance of about 408 km (253 miles), the ISS is actually “skimming the surface of Earth” too.

So, at what altitude can you start seeing the curvature of the Earth?

There’s a study titled “Visually Discerning the Curvature of the Earth” that answers this very question. Here’s the abstract of the study:

“Reports and photographs claiming that visual observers can detect the curvature of the Earth from high mountains or high-flying commercial aircraft are investigated. Visual daytime observations show that the minimum altitude at which curvature of the horizon can be detected is at or slightly below 35,000 feet (10,600 meters – about the cruising altitude of a passenger aircraft), providing that the field of view is wide (60 degrees) and nearly cloud-free.”

This study confirms that while you may get a sense of the Earth’s curvature at lower altitudes, a clear, discernible view of the curvature requires reaching at least the cruising altitude of passenger aircraft, with ideal conditions for visibility.

Sources and further readings

M. Özgür Nevres