1. During a lunar eclipse, the Earth's shadow has a spherical shape. 

The Moon is shadowed by the Earth during a lunar eclipse. Since the shadow is curved, the Earth must be spherical. The shadow would follow a straight line if the Earth were flat.

2. The disappearance of ships over the horizon. 

A ship gradually seems to drop below the horizon as it travels away from the spectator. No matter how far away an object is, if the Earth were flat, we could see into the distance.

3. The fact that gravity exists. 

Everything is drawn toward the center of the Earth by the force known as gravity. The effects of gravity on objects are compatible with the Earth's spherical shape. If the Earth were flat, gravity would be unevenly distributed, resulting in the odd and unpredictable ways that items would fall.

4. Images taken from space that show how the Earth's surface curves. 

A horizon that is visibly curved can be seen in images from space. The horizon would be straight if the Earth were flat.

5. The need for airplanes to modify their altitude in order to keep a constant height above the Earth's surface. 

In order to keep a constant altitude above the Earth's surface, aircraft must change their altitude. This wouldn't be necessary if the Earth were flat.

6. How the shadows of the Earth during a solar eclipse are formed. 

The Moon's shadow on the Earth during a solar eclipse is curved. The shadow would follow a straight line if the Earth were flat.

7. How satellites that are orbiting the Earth behave. 

The behavior of satellites in orbit around the Earth is compatible with the planet's spherical shape. Satellites would operate differently and possibly be difficult to launch and keep in orbit if the Earth were flat.
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