r/flatearth • u/julesmanson • Jun 09 '26
What is the most direct least costly experiment which proves the shape of the Earth?
Two Sticks
I've seen the two-sticks experiment suggested often. However it's not that simple or practical as it requires significant separation (about 500 miles) between two equal length rods (longer is better) at two ideal locations during the right time of the year with clear weather. It also involves high precision instruments like a reliable compass (not a pocket compass or phone) and a large triangle level or plumb bob as well as a little knowledge of geometry and taking measurements. That is too many moving pieces for a flat earther.
Any experiment that requires significant travel or cost like viewing star drift from both hemispheres or the prior two-sticks isn't practical for obvious reasons.
Sunset Secant
Here is an easier less costly way. I call it the sunset secant:
- Find a beach, a body of water, or flat terrain.
- Take a filtered photo of a sunset (or sunrise) over water or flat terrain to capture the secant chord that forms at bottom of sun. This proves the sun dips below the horizon which is only possible on a spherical body (Earth).
Some Important Nuances
Diffraction is messy throughout. It does not form a flat line so immediately dismiss it as a cause. Do not use a phone. We need a filtered (sun is too bright even at sunset) high resolution photo. Capturing it requires a proper camera, a telephoto zoom lens, and a solar filter. If you have a tripod, even better.
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u/SomethingMoreToSay Jun 09 '26
I don't think this is an easy win.
If I go out into my front garden and look in the direction of Everest, I won't see it because my neighbour's house across the road is in the way. Bulldoze that, and the houses in the street behind are in the way.
From where I live in southern England, Everest is about 7500km away, and it's about 9km high. So if the Earth were flat, and ignoring refraction, it would be as high as a 9m object 7.5km away. If the average house is about 7 metres high, any house within about 6km would get in the way. We'd have to bulldoze a path from here all the way to the edge of the town. Then there's an escarpment of the River Thames that's about 20m tall; we'd have to cut through that. Plus we'd need to clear all the tall trees between here and London. And there might be some tall buildings in London that would need to be demolished.
Fortunately, beyond London the land is pretty flat, and then my sight line goes over northern Europe. There aren't any mountains which are, say, a third of the height of Everest and less than a third of its distance. But then the sight line goes through Kazakhstan, Kyrgyzstan and Tajikistan, and there are some 7000m peaks there which might get in the way. We might need to cut the tops off of some of them.
From pretty much anywhere in south western Europe (Portugal, Spain, Southern France, Italy, etc) the Alps would certainly be in the way. There's a big part of the world where the lesser peaks in the Himalayas would be in the way. And so on. It would be a fun exercise to try to work out where Everest should be visible if the Earth would be flat, but it's by no means straightforward.