Summary:
- The Earth appears flat to the naked eye, but it is actually a spherical planet. This is due to the curvature of the Earth's surface being too gradual to be easily perceived.
- The horizon line, where the sky meets the Earth, appears flat because of the Earth's curvature. As you move away from the horizon, the curvature becomes more noticeable.
- The Earth's spherical shape can be observed through various methods, such as the way ships disappear over the horizon, the different constellations visible from different latitudes, and the shadow cast by the Earth on the Moon during a lunar eclipse.