Studies place the threshold altitude for seeing Earth’s curvature at about 35,000 feet.
Obviously space, or very high altitude, is your best bet. Unfortunately however, although space tourism is edging ever closer, it’s still not quite here which means that we can rule out that particular vantage point at least for the time being. Until a decade or so ago, Concorde was the next best thing. I took the above photo from a British Airways Concorde at about 58,000 feet on a “trip to nowhere.” It was taken with my brother’s old Pentax SLR and a standard 30mm (ish!) lens. Pressing my nose against the aircraft’s window and gazing from side to side, the curve was even more pronounced than the photo suggests, but these days I have to settle for those pictures to assure myself that BoB is mistaken.
Although Concorde no longer flies, there are similar aviation opportunities using retired military fighter aircraft in Moscow. Sadly, they make Concorde look like a bargain which means that most of us must turn to more terrestrial alternatives. But is it possible to view the curvature of the Earth without taking to the sky?
When I was in Chile a short while ago, I met a couple from California who had started their travels on Easter Island. They claimed that while standing on a particularly high point and gazing out at the endless ocean, they could clearly make out the curvature of the Earth with their naked eyes. Many of us have had similar experiences when perched on cliff tops and looking seaward, but is it just our minds playing wishful tricks?
Earth curves at about 8 inches per mile, but the distance one can see depends on height. For a six-foot-tall person, the curvature is approximately 3 miles away. This is a geometrical finding since the human eye cannot see a 24-inch curve from 3 miles away. Studies place the threshold altitude for seeing Earth’s curvature at about 35,000 feet. Even at this height, it is difficult to discern the curve as the observer requires a wide-angle of view. Since the distance of the horizon depends on the length of a person, it is possible to see the Earth’s curvature while standing on a raised position. For a person standing at the summit of Mount Everest, which is about 29,029 feet, the horizon is approximately 230 miles away. On a clear day, it is possible to see such a distance, but 230 miles is not enough for the human eye to discern an expansive curvature like that of the Earth. It is, therefore, possible to see the horizon from the top of Mount Everest but not Earth’s curvature. If we consider the effect of refraction, the horizon appears even further. Cold weather raises the atmospheric refraction making it possible for people in colder regions to see further. Secondly, clouds hover above the ground level and can be seen further than the surface. As much as the weather aids our view, it can also distort it. Precipitation and fog scatter light, making it impossible to see features visible on a clear day.
Photographing The Curvature
There are thousands of photographs on the internet of people claiming to have photographed the curvature of the Earth. Scientists have dismissed these photographs as fake or misrepresented. In almost every scenario, the curvature is caused by the distortion of the camera lens. If one lifts a camera above the center of the frame, then the right and left edges curve inwards to mimic Earth’s curvature.
Where Can You See The Earth’s Curvature?
The Earth curves at about 8 inches for every mile, but this distance is too minimal for a human being to discern the curvature. Even while on top of Mount Everest, it is impossible to see the curvature. Studies place the threshold to see the curvature at 35,000 feet, but even at this height, one must have at least a 60° angle of vision. Very few commercial flights make it to such heights, and therefore the Earth’s curvature is out of reach for many people. The best place to see the curve is in space. Astronomers in the International Space Station can not only see Earth’s curvature but also its spherical shape.
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