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 we are atop a high mountain or in a passenger plane, but comparatively, even in the case of the plane (planes fly higher even the highest mountain on Earth – the Mount Everest, commercial aircraft typically fly between 31,000 and 38,000 feet – about 5.9 to 7.2 miles – high), we’re just skimming the surface of our planet. So, how high do you have to be to see the curvature of the Earth?
What do you mean by the “curvature of Earth”?
Technically, you can see the curvature of Earth even at the sea level. Even the ancient Greeks knew that the Earth is round: A ship on the horizon moving toward the viewer will gradually appear with the masts first, followed by the superstructure, then the hull.
From just 3 meters (10 feet) above the surface, you can see the horizon 6.2 km (3.85 mi) apart. If you’re 30 meters (100 feet) high, you’ll be able to see up to 20 km (12.5 mi) away. This is one of the reasons why, at least from the sixth century BC, ancient civilizations understood that the Earth was curved, not flat.
So, the real question here is: “at what altitude you can 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 curvature of the horizon), though, but that would prove nothing. Earth is big.
The curvature of the Earth: at what altitude you can start seeing it?
There’s actually a study answering this question titled “Visually discerning the curvature of the Earth67 ” and 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.”
Scott Manley also created a video about this.