Photographing the Curvature of the Earth: Trickier Than You Think
November 07, 2014
Many people claim to have photographed the curvature of the Earth. But the curvature they show is not that of the Earth. In almost every case, it's caused by barrel distortion in the camera lens. If the horizon is placed above the middle of the frame (top photo), its left and right edge turn down, mimicking a curvature in the sense expected of a round Earth. If placed below the middle of the frame (bottom photo), the left and right portions turn up – the wrong way! Barrel distortion happens because the image scale (degrees/pixel) decreases away from the optical axis. This occurs when a sphere (celestial sphere) is projected onto a flat surface, the focal plane of the camera. The wider the field of view, the more evident the barrel distortion becomes.
Earth’s curvature can't be visually seen from any location on the ground, even from Mount Everest. Studies show that the threshold altitude for seeing the curvature is about 35,000 ft (10,668 m). Even then, it's barely discernible and the observer must have a wide angle field of view. Only aircraft flying much higher (commercial jets sometimes climb above 40,000 ft or 12,192m) offer an easy view of the curvature.