 has a hard time explaining eclipses in general, but a lunar eclipse is especially difficult for them. A lunar cclipse occurs when the spherical Earth moves directly between the Sun and the Moon. The Earth blocks all or part of the Sun’s rays from reaching the Moon. A total lunar eclipse occurs with the configuration shown in Fig. II.11. There will be a darker shadow called the umbra, and a less dark region called the penumbra. A total lunar eclipse occurs when the configuration is such that the Moon lies entirely within the umbra. When this occurs, the only light that reaches the Moon is sunlight that is refracted by the Earth’s atmosphere. The green through violet part of visible sunlight gets filtered out in this process, and does not appear on the Moon. Red light is refracted least, and so the Moon appears as blood red during a total lunar eclipse.
As the Sun, Earth and Moon move, the Earth’s shadow can be seen moving across the Moon. Since the Earth is a globe, its shadow is an arc of a circle. During some lunar eclipses we can see the shadow of the Earth move across the Moon – yet another proof that the Earth is a globe, and that it moves. Fig. II.12 shows images from a total lunar eclipse in 2019.
A lunar eclipse presents major difficulties for Flat-Earthers. Since the Earth is supposed to be a flat stationary disc, there is no way that the Earth can be interposed between the Sun and Moon. Hence Flat-Earthers must invent something to explain why one sees a shadow of a spherical object obscuring the Moon.
For many Flat-Earthers, this mysterious body is an “Antimoon.” This is supposedly a body whose orbit is extremely close to the Sun. It cannot be seen because the Sun is so bright that it ‘hides’ the Antimoon from view. Of course, this is all nonsense. The only purpose for the Antimoon is to provide a lame excuse why the Earth’s shadow appears to cross the Moon.
However, the Flat Earth Society acknowledges that the body obscuring the Moon could be some other object, which they call the Shadow Object rather than the Antimoon. “There is also a possibility that the Shadow Object is a known celestial body which orbits the sun, and which projects its shadow upon the moon; but more study would be needed to track the positions of Mercury, Venus and the sun’s asteroid satellites and correlate them with the equations for the lunar eclipse before any conclusion could be drawn.”
Here, we happen to agree with the Flat Earth Society. The “shadow object” is a known celestial body – it’s the Earth, dummies! But this waffling is what one expects from an organization that is determined to get the wrong answer, or to introduce ad hoc pseudo-explanations devoid of other motivation for every observable that causes them trouble.
II.5: The Earth’s Rotation
In Flat-Earth theory, the Earth is stationary, which means that it does not revolve around the Sun. Flat-Earthers also deny that the Earth rotates once per day. They spend much time heaping scorn on anyone who believes that the Earth moves.
In particular, they claim that it is not possible that the Earth, together with its bodies of water and the lower atmosphere, are all rotating at the same speed. They present a “demonstration” that they claim proves the Earth could not possibly be rotating. Take a tennis ball and soak it with water. Then spin the tennis ball. The water flies off, as shown in Fig. II.13. Flat-Earthers say “See? The water flies off the tennis ball when it spins. This is exactly what would happen to water on Earth if it was spinning!”
Let’s see why the “wet tennis ball” is a terrible analogy. The tennis ball produces a gravitational acceleration inward on the water. There is also, in the reference frame of the spinning tennis ball, an outward acceleration, the centrifugal acceleration due to the spinning of the ball. (From the viewpoint of an observer on the ground, this just represents the effect of the water’s inertia in the absence of a force that will cause it to spin with the ball.) We can easily calculate those accelerations; given a reasonable rotational speed 