The Sun and the Moon appear about the same size in the sky, but they are not perfectly the same size, and their sizes are not constant because their orbits are not perfectly circular.
Flat-Earthers claim it is too much of a coincidence that the Sun is perfectly 400× larger than the Moon and perfectly 400× farther, making them appear perfectly the same size. In reality, the Sun and the Moon are not perfectly the same size in the sky.
The distance to the Sun is often stated as 149.6 million km. However, it is the average distance. Earth’s orbit around the sun is not perfectly circular. Sometimes the sun is closer than the average distance, and sometimes it is a little farther away. As a result, the apparent size of the sun changes. The apparent diameter of the sun hovers between 0.525° and 0.542°.
The orbit of the Moon is even more eccentric. The distance to the Moon is often stated as 384400 km. Again, this is the average value. The actual distance is somewhere between 356400 km and 406700 km. When the moon is at the closest distance, it results in the largest apparent size of the Moon. We call it a supermoon.
During a solar eclipse, the Sun and the Moon’s apparent size determines whether it is a total eclipse or an annular eclipse. If the Moon appears larger than the Sun, a total eclipse occurs. Conversely, if the Moon appears smaller, then an annular eclipse occurs. If they are about the same size, a hybrid eclipse occurs, where it appears as a total eclipse in some areas and an annular eclipse in another.