Flat-Earthers often commit the fallacy of moving the goalposts. When their claim has been proven wrong, they would revise their claim and demand another evidence that is harder to fulfil. They would do this repeatedly until they present an unfalsifiable claim, a claim that is impossible to prove.
Some flat-Earthers consider crepuscular rays as evidence that the Sun is not far. In their mind, the Sun is only about ±5000 km circling above us. In reality, the actual distance of the Sun is ±150 million km.
“The Sun and the Moon have been observed to appear in the sky at the same time during a total lunar eclipse. This cannot happen if the Earth is round because the Sun, Earth and Moon are supposed to be in a straight line during a total lunar eclipse. So, the globe Earth model is wrong!”
Some flat-Earthers observed the Sun and Moon appear at the same time during a total lunar eclipse. Predictably enough, they pick the most far-fetched explanation, and conclude the Earth is not round. But in reality, this phenomenon is well documented and clearly explained.
“Looking at the pictures of the progression of a lunar eclipse, the Moon turns red, but there’s no apparent change of brightness of the Moon as it progresses from full moon to total eclipse. Therefore, a total lunar eclipse cannot be the result of the Earth casting its shadow on the surface of the Moon.”
Some flat-Earthers —presumably never seen a total lunar eclipse in person before— actually claim that.
The Moon turns red during a total lunar eclipse. But if the Moon is completely in Earth’s shadow, then how does it turn red?
The atmosphere of the Earth acts like a giant lens and refracts some of the sunlight into the surface of the Moon.
Apparently it is a very common misconception that the phases of the Moon is caused by the Earth’s shadow. Not only among flat-Earthers, but the general public as well. The difference is that flat-Earthers will usually jump to conclusion, and have some outlandish interpretation about this.
In reality, the phases of the Moon happen because we see a different sunlit part of the Moon at different time. Not because it is over the shadow of the Earth.
Practically every depiction of the Sun, Earth and Moon is drawn not to scale. Flat-Earthers sometimes use this fact to point out the alleged “failure of modern science” to describe motion of celestial bodies, or something like that.
But in fact, the reason is simply that it is practically impossible to create a model of the solar system with real scale, using static images, that is still effectively describes the objects it is trying to explain.
Some flat-Earthers claim there is no non-stop long-haul flights between two locations in the southern hemisphere. Flights need to make a stop in a location in the northern hemisphere because the distance will be too far and such flight will traverse the northern hemisphere, or more accurately, the center of the Earth according to their model.
Flat-Earthers often commit the fallacy of ‘hasty generalization’. They would draw the conclusion from limited sample that fail to represent the entire population. Sometimes they would even draw the conclusion from a single case, and it becomes the fallacy of ‘lonely fact’.
Furthermore, they would deliberately cherry-pick cases that support their position, and use those to disprove the other cases that are against their position.
If we walk by pushing our feet against the ground, birds fly by flapping their wings against the air, and fish swim by pushing their fins against water; then how can possibly a rocket move in a vacuum?
Rockets are able to move in space by making use of the law of nature described in the Newton’s laws of motion, and the law of conservation of momentum.