Some proofs of a spherical Earth are:
>The visibility of distant objects on Earth's surface: On a flat Earth, the ground itself would never obscure distant objects. However, on a spherical Earth, the horizon is closer when viewed from a lower altitude, and farther when viewed from a higher altitude. This means that objects that are beyond the horizon cannot be seen from the ground, but can be seen from a higher vantage point, such as a ship's mast, a mountain, or a plane. For example, ships travelling on large bodies of water disappear over the horizon progressively, such that the highest part of the ship can still be seen even when lower parts cannot, proportional to distance from the observer.
>The lunar eclipses: A lunar eclipse occurs when the Earth passes between the Sun and the Moon, casting a shadow on the Moon. The shape of the Earth's shadow on the Moon is always a circular arc, regardless of the location and time of the observation. This can only be explained by the Earth being a sphere, as a flat or any other shape would produce different shadows depending on the angle.
>The appearance of the Moon: The Moon appears to have different phases depending on its position relative to the Earth and the Sun. The shape of the illuminated portion of the Moon can be explained by a simple geometric model, where the Moon is a sphere that reflects the sunlight, and the Earth is also a sphere that blocks some of the sunlight from reaching the Moon. The phases of the Moon can be predicted and observed with accuracy using this model. A flat Earth would not be able to account for the consistent and regular changes in the Moon's appearance.
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